As a computer engineer who fixes my own vehicle, by far this is the first video I have seen on you tube that lives up to the standard of being intellectually stimulating. Well done and thank you for taking the time to explain the nuances and logic in detail. I am subscribing to your channel. 👌🏽
I’m a non-certified female service tech in my 20’s starting out at a small mom ‘n pop shop. Even though I’m around cars all day and could swap almost anything you could point at it’s been difficult for me to mentally conceptualize how everything ties together or come up with the right approaches to problem solving. Not to mention it’s hard for my bosses to find time to explain things to me and half the time I’m havnt been sure what questions to ask. I’ve been coming home after work to watch your videos oldest to newest (I find the poor video quality to be quite endearing btw haha) and I love the way you describe the basic fundamental rules in a structured and logical path. I have DESPERATELY been needing it!!! It’s been making my day job 10x more engaging and meaningful to me! Everything is more interesting now that I’m starting to understand the genius of design behind it all haha! I am eternally grateful to people like you who give out such valuable information to a public forum. It’s been changing my little corner of life in nothing but positive ways. Hope you see this. Thank you Matt :)
So glad to hear that and I hope this helps you navigate some of the challenges you are sure to find being a female in the industry. I actually have a little helper on some Friday- a 20yr old female tech student who is very similar to you- she is trying to learn the diagnostic concepts as well. I hope both of you cross paths some day!!
Three wires • fuel • spark• gravity • physics. Get past fuel and spark. Except physics, gravity and the elements and the computers control over everything. The big thing is three wires. ⚡️ Old Pablo Tucson, everyone is a boxer or mechanic. Not liking cardboard, I choose mechanics. First thing I said, “I hate the electric shits” If… That’s All There Is. Now I’ve Seen Everything 🔫
FINALLY someone who explains THOROUGHLY and so professionally, that makes understanding the intricates easy. THANK YOU for your videos, your a true car enthusiasts asset. Will stay tuned in to learn more!! YOUR AWESOME!
What an amazing, clear, comprehensive explanation of STFT and LTFT and their relevance to engine performance as well as trouble shooting process. Thank you so much.
All I can say is one outstanding person to describe fuel trims. For about seven years I have been digging for information on fuel trims kind of hard to understand but this just nails it!!!! Such valuable information to have. I just have to make sure that I can retain it. Got to have this for future thank you brother.
One of the most informative videos in my opinion with a guy who cares enough to share and explain his knowledge on you tube, whether you're familiar with fuel trim or not this was very helpful at least for me .great effort sir . thank you
@@johnshaw5001 not sure if you listened but he never said that STFT set a code. Instead, he said STFT is an immediate response to the percentage of fuel that the pcm is adding or retracting... If, in a given case, STFT has reached 20-25%, meaning pcm is adding 20-25% more fuel to keep the engine running somewhat normally; after a while, this condition is set as the new normal thing to do by the pcm to keep the engine running and the LTFT percentage (The fuel trim percentage noticed after "a while") is set to this 20-25%. Therefore, now the pcm takes this increase seriously and set a code for the pro to figure out what has caused this anomaly. Note: if you are a pro, why don't you contradict intelligently with details instead of just denigrating with a sentence in which you claim to be a pro? Where is your youtube video on this subject? Share your knowledge Mr Pro. If what you must say is not more important than silence then BE QUIET HATER!!
@@SchrodingersBox would you be able to help me out...pretty much figured had a vac leak (06 envoy) ..when warm stft is -3/3 and left is 10-12 ranges...when accelerating stft goes up to 5-6 ltft comes down to 7-8... but sometimes the scanner will jump and show stft like 5-6 and ltft will.be 3-4... and when cold and idling the numbers jump around a bit..
Techs/mechanics, electricians, plumbers, etc struggle in their respective trades for lack of knowlege on how things really work. Then comes someone like Matt who by previous trade was a scientist but has the smarts to be competent at almost anything. We in the auto repair trade are fortunate to have his perspective and would do well to take advantage of what he can teach. I have been in the auto repair field since 1977 and just had greater understanding of Fuel Trims since watching this.
I’ve worked industrial process control related to precision furnace combustion for over 40 years and you’ve explained the fuel system in modern vehicles in a concise and easy to understand manner that surpasses any teaching moment I’ve ever had. Thanks for sharing.
You are a god! Using what I learned from this video I solved a too lean code in one drive cycle, leading to a failing MAF. Replaced the MAF and am now driving with a smile and without a fault code.
This series is the absolute authority on the matter of Fuel Trims/Advanced Driveability Diagnosis BY FAR -- I've come back to this series countless times in the past three years and they have helped me grasp more on the topic than in the previous 8 years of my career as a tech -- Many thanks sir!
thanks my friend. This video is actually used in several tech schools as part of the curriculum in fact. I think it’s the most important video on the whole channel. probably 80% of all my diagnoses start by using fuel trim.
Found your channel today while browsing for info on my 1998 Pontiac Trans Am WS6 with intermittent hard shifts. I am OEM and technician in the wastewater industry. I have grown weary of so-called professionals throwing parts at my vehicles without proper diagnosis. Hence, I do much of the maintenance and repairs on my vehicles myself. I am certainly not at your level of expertise. However, in diagnosing problems with pump and control systems in my field of expertise, I have to rely on good data. Obtaining good data requires critical thinking. I appreciate your passion for understanding mechanical systems and your persistence to make sure a particular problem is properly diagnosed. Thank you for sharing your knowledge. I also enjoyed your video of diagnosing the exhaust restriction for an older lady. I am glad to know there are others like me who share old school values such as not charging for work that was of no benefit or value to the customer.
+Schrodingers Box your an idiot, i have been an ASE master tech and GM world class tech for a little more than 20 years and diag cars with fuel trim issues on a daily basis and no way does a MAF fuel trim get worse with higher rpms. I will show you my credentials, lets see yours. Quit spouting off shit that you have no clue about, well the rest you were right about but you are honestly totally wrong about MAF fuel trims getting worse with higher rpms.
troopbd I dont have to call you an idiot- you're doing it yourself,. Show me ONE case study where a vacuum leak got WORSE fuel trim under load and better under idle OR even one case study where a dirty MAF showed normal fuel trims under load but higher at idle and I'll publically aplogize. If you don't do that I'll just delete you from this channel- or better yet, delete your comments and leave the ones that just make you look like an idiot. GO! Time is wasting!
This was EXTREMELY helpful for me, one that has not even unwrapped my new scanner. I took tons of notes. I have an Explorer that runs really rough and it's burning tons of fuel. I am about to watch Part 2 and then I will begin my interrogation in the morning. My only complaint is that you did not provide your name. Your art skills are just fine. Thank you again sir.
I totally understand it !!! I learned. I’m an Idiot And reclaimed myself to fix my vehicle by watching this video which I should of watched this before I was an idiot Thank you for the excellent fantastic video
This video definitely helped me understand the difference between lean and rich . The content was very informative and clearly outlines possible scenarios that might trigger these symptoms.
Wow, I'm glad I came across your videos and I can't even thank you enough for sharing the knowledge about all this. I'm knew to working on cars and one of the things I like to do is understanding why things fail as opposed to just replacing things. This is the best video I've seen in regards Fuel Trim, something I knew very little about but the way you explain it in your video makes it very simple to understand. Thanks a lot my friend.
This is sooo helpful! I'm learning fuel trims for the first time in school and it can be kind of confusing but you do a great job of explaining it clearly. You'd be awesome to have as an instructor. Thanks so much!
Best teaching thankyou a lot. I have 2005 4.8 vortec . I fund 2 code P0301 P0171, Fuel treams was LONGFT1 0.25 Shortft1 0.0 i didn't change o2sensor . I check than i found the broken vacuum tube which is located on the top rear right side of engine goes to purge. I replaced the 3" rubber vacuum tube than 0171 code erased. For p0301 , i test coil and spark plug and wires , they working good. Than i pulled out first cylinder injektor it was realy dirty than using carb.cleaner and c c intake cleaner applyng 45ps air into injektor all the dirts come out. After installing back injektor . P0301 code also cleared. Engine runs Smooth and burns lees fuel.
When helping my fellow car owners, i guess because I am a female and I shouldn't care about any of this, I'm not expected to understand this. My problem is I have to fix my own cars. My mother only has me. This has changed my life and made me a mechanic, rather than a me_can lol. Thank you for your time and understanding.
This is one of those video's where you realize that it's not about a fancy whiteboard or how big it is. This is a video where you realize that it's all about COMMUNICATION!
Wow, I found this very helpful and wanted to give this guy a long THANK YOU for his energy and passion, but I see that other people have done this in great detail ...so I gave a quick thumbs up.
Thank you so much for making this video!!!! After 2 days of head scratching, I was finally able to pinpoint my problem to a clogged cat once understanding how to interpret fuel trim data and correlate to O2 readings. Your videos have greatly enhanced my diagnostic abilities. Many many thanks!
Matt: I'm sorry this is so long, but I hope you find it interesting. Your video provided a rational and super-helpful guide for me to follow in trying to diagnose a problem with high fuel trim at idle. (Fuel trims 20%+ at idle, improving at higher RPMs.) Following what you explain in your video, I came up with the hypothesis that I probably had an intake vacuum leak. After much testing though I had to conclude there was no vacuum leak. Testing also showed I didn't have a fuel delivery problem - no problem with fuel pressure, injectors, O2 sensors, exhaust leak, exhaust restriction, leaking cold start air enrichment device. I cleaned the MAF, tested MAF voltage at various RPM/load settings and checked the MAF wiring harness/grounds. All tested normal. The only unusual finding appeared when I compared fuel trim against MAF grams/second output on a scan tool. At steady idle, the MAF grams per second reading was varying by as much as a gram, and the lowest grams per second readings and highest fuel trims numbers seemed to coincide. Eventually I had to consider the hypothesis that the MAF was underreporting idle air flow to the ECU. I found this article very helpful: www.motor.com/article.asp?article_ID=839. The author concludes the article by saying, “If you can't locate a fuel or air delivery problem to explain high or low fuel trim values, don't overlook incorrect MAF...input values.” Cleaning the MAF with CRC MAF cleaner made no difference. But after I replaced the MAF sensor the fuel trims returned to normal. (LTFT Now 0% with STFT +/- 5% at idle). The grams per second reported from the MAF at idle now varies across a more narrow band, and never falls below 3.5 g/s. (With the bad MAF it was falling as low as 2.8 g/s.) Replacing the MAF fixed the problem. I decided that replacing the MAF was a reasonable thing to do, even though my testing hadn't absolutely proven 100% that the MAF was bad. Replacing the part seemed prudent, but seemed to fall short of the standard of empirical/scientific justifiability you have set. I guess you could say that replacing the MAF was itself the empirical test that proved the MAF was bad. But that kind of thinking seems like a slippery slope that could lead to becoming a mindless parts replacer. What other tests could I have done to test the MAF before I replaced it? The voltage tests I found in the Factory Workshop Manual and in Paul Danner's book suggested that the MAF was fine. I spent a lot of time testing and ruling out hypotheses related to vacuum leaks and fuel delivery and I was running out of patience. Even though I thought it was a reasonable thing to do, before I could bring myself to replace the MAF, I had to overcome a psychological hurdle: Namely the sound of your voice in my head saying, “If you replace the MAF, you're an idiot!” As much as I want to be a member of “the 2%” and not “a mindless parts replacer” I guess sometimes practicality demands a lesser standard. I think the theme of “I want to be a member of the 2% and everybody else is an idiot” has great rhetorical appeal and gives your videos an enjoyable dramatic character. You might find this interesting to read. It comes from a summary of the theory of drama elaborated by the great American philosopher and literary critic Kenneth Burke. He says that all successful dramatic narratives include a victimage or scapegoating mechanism: “Victimage is the process of scapegoating. Here, the speaker blames an external source for his ills. According to Burke, there are two different types of scapegoating, universal and factional. In universal scapegoating, the speaker blames everyone for the problem, so the audience associates and even feels sorry for the victim, because it includes themselves. In fractional scapegoating, the speaker blames a specific group or a specific person for their problems. This creates a division within the audience. The victim, whoever it may be, is vilified, or made up to violate the ideals of social order, like normalcy or decency. As a result, people who take action against the villains become heroized because they are confronting evil.” (from wikipedia en.wikipedia.org/wiki/Dramatism) The dramatic narrative you've constructed in your videos is an example of fractional scapegoating: it is the mindless parts replacers who are the villains, and it is us - the tiny minority of scientists - who are heorized because we are confronting their stupidity. This isn't a criticism by the way. Burke's claim is that all dramatic narratives work this way. And your video was invaluable in providing me with a strategy to follow in forming and testing hypotheses. But eventually, in the process of finally fixing the car, I also had to - temporarily I hope - embrace the role of idiot.
Thank you for sharing your experience. I'm working on a 97 Ford Ranger 2.3. I had been noticing sort of poor gas mileage for months; then got a check engine light. Scan tool showed a potential problem with the charcoal canister purge valve. Not interested in empirical testing when I can just grab the part off another rig (But, like you said. That's an empirical test too.) Since I was right there with the scan tool, I pulled up my fuel trims and noticed right away that I had long term over 20, though it would drop under load. Back home; I checked for vacuum leaks and came up with squat. I watched this video a year or two ago, and thought I'd watch it again, to see if my memory of fuel trims was faulty. But first I scrolled down through the comments. Your comment about hearing his voice calling you an idiot, or otherwise denigrating you is almost always on my mind when working on a car, and it's saved me some pointless part replacing since I discovered this channel. I just thought it was funny, how we were in just about exactly the same frame of mind. My wife walked in and asked if I fixed my truck; and I told her: "Maybe. At least what I thought was a problem. But my fuel trim's really high; and I don't seem to have any vacuum leaks. Which is about all I can think of that would cause it... but I guess a bad MAF could do it too..." And here's your comment. Same problem as mine. (apparently) I've been suspicious of my MAF for quite a while now, and I'm thinking that's probably where I should be looking next.
Joe Sevy I far from being a ace mechanic but would it set a code for the maf ? I’m dealing with a code on a gm p1174 just wondering if it’s bad gas ? I also think the plugs which are iridium but there at 116000 and I know that it’s need to be changed and go from there .. check for leaks .. there all saying you got change all your injectors and get reprogram not so fast .. the car starts on a dime took on the highway with good response to throttle.. any inputs thanks
@@anthonypapaleo1940 You're really talking to the wrong guy here for that particular code especially! However; I can't see any possible logic in suspecting the MAF in this problem. The MAF detects total air flow to the engine; it doesn't have anything to do with the detection of a rich/lean imbalance between cylinders. The MAF can be, good, bad, or ugly without giving that code. If you're using a non oem air filter especially, I can certainly recommend cleaning the MAF with MAF cleaner, and after that many miles it's probably taken a bit of a beating. But, obviously, your only legitimate reason for changing it at this point is the same one that applies to changing the plugs. As (expensive) maintenance rather than waiting for it to fail. But, I'd be shocked to find that it had anything to do with your situation. If your plugs have 116,000 on them, I'd suppose they're about due for a change, but I certainly wouldn't have much hope for that to solve the problem as there'd most likely be a misfire p0300 code along with with the p1174. Though I can tell you that I've changed plugs with 144,000 miles on them that were obviously in really bad shape without ever throwing a code. So, if you try it and it helps: Yay! Just don't expect much. "Bad gas"? I suppose it's possible, but not too likely from what I can find out. I'm rather skeptical about something getting sucked out of the tank and past the filter being bad enough to mess with the injectors, but only enough to cause this code. Though, it's entirely possible for the filter to be clogged badly enough to interfere with fuel pressure; again. I'd expect another code, p0174 and poor performance. Though your code is associated with injector problems; injector problems are also associated with engine idle and power problems. Since you don't have idle or power problems, as far as you can tell, I don't think you're too likely to get anywhere there either. Still, you're the one who feeds it gas. If YOU think you've been giving it bad gas, start giving it good gas. If it sits for long periods of time, then good gas could have gone bad. But again. The whole engine gets the same gas. You're looking at an imbalance between the cylinders. Go ahead and use gas additives if you want. Some swear by them, some at them. My opinion is they sometimes do some good, and I've not seem them do any harm. Just don't expect it to fix the problem. I'm also rather skeptical, for the same reasons, that one or more of your injectors has a problem, sufficient to cause this code, yet not bad enough to throw another code or cause problems with idle or performance. There's no way I'd even think about putting a set of injectors in it unless that's something I was already considering for some other reason. You can do a simple test yourself on the injectors to look for obvious potential problems. Simply disconnect the electrical connector to each injector and check the resistance of each one. If none of them are greatly different from the others, they're unlikely to behave differently when they receive a signal from the ecu. This may be a lousy way to diagnose injectors, but I've done it successfully before. The problem is that this can only find one possible problem. The injector could well be damaged, perhaps enough to cause your problem, without this test telling you anything. But, it's something you CAN do, and it WILL eliminate one possibility. You can also check the voltage being supplied to the injectors, but I'd expect that to show up as a code as well if it were the problem, and if it were a fault in the wire I'd expect the injector to completely fail, again, throwing a code. I'd much more expect the problem to be one with an intake leak of some sort, which can be very tricky to track down. You'd suppose a leak would automatically be worse at idle than at cruising speed, but that's not always the case. Finding a leak that only presents itself at speed is going to be quite a problem. Still, that's where to start. Change the plugs, because it's time; then start checking for leaks. If you find one; that's something that needs fixed at the very least; and a very likely cause of your problems. Another symptom of a vacuum leak is if the engine races at startup. If your engine, when started, revs to a significantly higher rpm when started than it used to, or than other similar engines do; you've likely got a vacuum leak. Since all the likely causes other than vacuum leak or general engine deterioration usually cause idle or performance issues, and you're not reporting any idle or performance issues, and there're no other codes, I really doubt that you're going to get anywhere with the injectors or fuel system. The most likely culprit is going to be a manifold leak of some sort. If you have some kind of scanner that can show you fuel trims in real time, I'd expect long term fuel trim to be somewhat high if you have a small vacuum leak, anything over 10 and I'd almost guarantee there's a leak. If you don't have a scanner of any sort I'd recommend getting a cheap BAFX bluetooth scanner; buying the Torque Pro app, and using that until you can get something better. I can't make any recommendation for what that better scanner would be because I can't make up my mind what scanner I'd get even if I could get anything I want. But, even if you can't tell the engine's getting more fuel when you use propane, starter fluid, or whatever to find your leak; your ecm can, and it will change the fuel trim to compensate. That's why you need to be able to monitor the fuel trim as you're looking for your leak. So, what help have I been? Not much. The problem with so much of this stuff is that it gives us problems that are only problems because we're informed about them. If not for this code, you literally wouldn't have a problem to fix. Or at least that's the way it sounds to me. Or, maybe it just gives us the opportunity to fix a small problem before it gets to be more serious. Hopefully I haven't just added my ignorance to yours. Hope you fix your problem!
Joe Sevy Thanks joe my idol seems a little choppy but not bad but not racing .. also this code came up after my wife fill up at this one station.. so I’m taking the car to have the plugs changed , maf clean , throttle body clean ... I really don’t know what was done this car I just bought three months ago and also do my own maintenance but do the cold here in Chicago and no garage ... But like I said this only code I get no miss firing or any other code .. I really don’t like throwing parts at and till I know for sure . I will have the shop run a scan and see what’s up with .. thanks for any suggestions...
Hands down the best explanation I’ve ever seen on 02 sensor voltage telling short and long term trims what they need to do for the perfect 14.7-1 AFR. Can’t wait to to watch part two. Very useful information, thank you!
THIS IS GOLD!! Thank You for sharing this useful informations. My car runs bad when cold and I taught that mabe its the O2 sensor. But I found out that it doesnt work when cold. Next I will check MAP, throttle body and fuel pressure regulator. I changed the ECT sensor so tomorrow morning I will see if I figure it out.
Awesome video man, very well explained ! I wish other mechanics would watch. I got a p015b code on my 5.3l v8 with a rough idle. I took it it to a mechanic today and the first words where "02 sensor" ... my next words where "your an idiot " bye😂
Can't thank you enough for making this and your other videos. I learned to wrench on cars back when they had oil bath air cleaners so understanding the PCM has been a real challenge for me. Your videos break down how they work in an understandable way so I can troubleshoot to compotent level and not just guess what part to swap out. Keep up the great work, you are an awsome teacher. Thank You.
Great video!! Thank you so much. I had a check engine light on my 2000 Silverado. Both PO171 and PO174. Hooked my scan tool and checked the short and long term fuel trim. Found the long term steady above 20 percent. Took a closer look and found a vacuum hose had come off. Plugged the hose in and no more light. You saved me a couple hundred and I really appreciate it. Thanks so much!!
Well, Ive either been to idiots or scam artists. I've had the O2 sensor replaced, intake manifold, MAF sensor (2x) once I replaced myself and the second time the mechanic did it and charged me $400 for a 10 minute job, replaced the fuel pump, and on and on. Thousands of dollars later I still have the problem. Thank you for this video. You explain things very well for those of us that are novice auto DIYers. I think I'll be my own mechanic from now on. :)
Watched again. I have a V6 engine. I've got 2 air fuel regulators, 2 cats, and 4 O2 sensors with one exhaust. Going to check the manual again to be sure, I don't think it even covers this.
Hey man, I really want to thank you for your time and your talent explaining this to another mechanic, it’s not over simplified yet you’ve put everything into a much clearer perspective and probably made me a much faster worker. Thank you very much for that, to me there was always a little confusion in how to utilize STFT and LTFT in a proper diagnosis but now i see how and why it’s important.
You remind me so much of my son. Unbelievable! He explains computers to people just as you explain the workings of the engine. Same mannerisms and speaking style....Anyway, he's over 2000 miles away which is okay because I wouldn't want him to see his father going crazy over this 93 Chevy 1500 with a 4.3, and which I've changed every sensor and at my wit's end. I'm trying to watch all of your videos and taking what I can use I'm putting the rest aside. I'm not going to give up. I'm not a quitter. But I lay awake at night wondering if there was something I might have missed. That it seems I end up making it worse. It's a good little truck and I want to keep it. But most of all I need to figure it's out. Surging at idle. Misfiring at low idle and up to maybe 30 miles per hour. At higher speeds it feels like I'm pulling somebody with a rubber band but the engine sounds better. Sorry. I'm rambling. Thank you for the videos. Hopefully I'll combine them and get my truck back on the road.
@@SchrodingersBox unfortunately it's OBD1 and I don't have a scanner. I'm well adapt at troubleshooting with a voltmeter and basic electronics, so that's what I'm working with, in accordance to your videos in which you apply the voltmeter. Getting the 5 volts at the appropriate sensors, ran the TPS up and down, slowly and smoothly. Results were excellent. Against one of your cardinal rules, and having quite a bit of "reward points" at AutoZone, I replaced the oxygen sensor, IAC, TPS, EGR valve and the solenoid, ignition control module, and tested the primary and secondary on the ignition coil. (Low and high) and resistance was well within the specs. Testing with a vacuum pump I found no vacuum leaks. Getting some excess oil on the spark plug threads so replacing the valve cover gaskets now even though they look fine. I am getting terrible fuel mileage. No excess smoke from the exhaust, but has fairly strong order of unspent fuel. I've succumbed to the fact that this is my purpose in life. My mission from God. I'm on a quest to figure out what's the matter with this truck!!!! Lol Of course I'm kidding... but like you, I'm not satisfied with taking it to a dealer and have them them fix it. I need to do with myself and understand what the issue is and, more importantly, WHY the issue is. Lastly, I have a one way airflow valve ordered to make my own compression tester. I could buy one, but using the time 2 troubleshoot all the other things. Compression check should have probably been the first thing to do in case I'm wasting my time. But I'm enjoying this even though it's frustrating. If that makes sense. 🤔 I understand it's difficult if not impossible to diagnose a vehicle when you don't have your hands on it. Thanks for replying and if there's any other pertinent information you'd like, I'll do my best. Hope my book didn't put you to sleep. 😴Thanks again. P.S. I did the jumper thing between the A and B on the OBD1 Outlet to get the flashing codes. The EGR 13 is the only one I've ever gotten. Currently, there is no check engine light but the thing runs terrible. Especially at idle and just "getting going". Seems to correct itself at higher speeds except for that feeling of pulling something with a bungee cord or rubber band.
So many questions....Who is he talking to? Is Stoichiometry contagious? Who is making all of these fuel adjustments, a small squirrel with a screwdriver in the carburetor? Is this real life....? Is he tripping he looks like he is wired?
Wow, wow! super informative. Your explanation is clear and understandable. I wish i had learned this before my mechanic asked me to replace a host of sensors.
Thanks to your video I was able to figure out the problem with my car , Stft and Ltft 18% at idle but Ltft would drop at higher rpms but Sftf would not move even at higher rpms. , I tested fuel pressure was good, it turned out it was the fuel injectors, thank you very much!
Thankful i came across your channel, very informative and easy to follow. Was able to diagnose and fix a P0171 on a 2014 Nissan Pathfinder using the LTFT/STFT readings. Have to admit i had to fight my instincts/desire to gravitate to the sensors (MAF/02) as the source of the problem but i trusted the method and more importantly the "data". The data showed higher fuel trims at idle and improved (lowered) at higher RPMs. Started hunting for a vacuum leak and low and behold a bad crankcase breather hose (in the worst spot in the engine compartment) was the culprit. $7 bucks later and the fuel trims are headed in the right direction (just need to let it get to the new baseline and should be good). Thanks again!
Was a while ago now so do not exactly recall all the details but I do not recall any drivability issues. Think it was just the check engine light and maybe some reduced gas mileage that sent me hunting for the problem.
Thank you for the fuel trim explanation I have gone though all the tutorials on UA-cam and your explained it perfectly just as the computer reading 14.7.1 ratio. As for the people who dint agree with your tutorial the saying goes We Agree To Disagree. your work is appreciated.
Taken on a 175km trip now all looks good (touch wood) STFT around -1.6 Banks 1 and 2 LTFT around -7 Banks 1 and 2 and motor seems to be running smoother. Next I will check Fuel consumption Thanks for your help. Over here in Australia most of the mechanics I have spoken to about this problem just tell me to just reset the codes, this has made my head hurt for many years, my fingers are crossed. Graeme in OZ
Not trying to be a jerk, sincerely. But... There is a very wide spread misunderstanding of what a 14.7:1 Air:Fuel Ratio (AFR) means. It is often stated as a ratio of 14.7 parts of air for every 1 part of fuel. That is incorrect. And I have come across this error in factory training, discussions, classes, manuals, and even military training manuals involving emission control and fuel systems for engines. The correct way to state the 14.7:1 AFR is there are 14.7 pounds of air for every pound of fuel, or even more correctly in a 14.7 AFR the mass of air is 14.7 times the mass of fuel (weight and mass are related, but for the purposes of my comment I feel the use of a unit of weight vs using the word "mass" makes it clear what AFR really means). In short, for clarification, an AFR is a not volumetric measure based comparison between air and fuel. If you think about this for a moment you will realize that if it was a 14.7 parts of air for every 1 part of air, we would be seeing far less air being pulled into an engine. There are other implications that further point out the folly of a volumetric based ratio involving air when it comes to the density of air molecules for any specific volume at various temperatures and/or altitudes. There are other units of weight that are used as opposed to pounds, but despite the unit of weight used the ratios of the weight of air compared to the weight of fuel remains unchanged. Accordingly, it is also correct to say the 14.7:1Air:Fuel ratio is also described as being 14.7 grams of fuel for every 1 gram of fuel. For anyone who doubts that I am speaking accurately, please Google the following text, then read what Wikipedia says. WHAT DOES A 14.7:1 AIR FUEL RATIO MEAN WIKI As far as how widespread the incorrect description is, one only needs to drop "WIKI" from the Google search string above, then begin to read some of the descriptions, such as this one from Summit Racing, where they say in an article named, "Engine Basics - Air/Fuel Mixture," the following, "AFR stands for air to fuel ratio. Fuel doesn't burn on its own. It has to be mixed with air. AFR tells you how many parts of air are mixed with each part of fuel. For example, a 14.7:1 AFR (or just 14.7) means the mixture is 14.7 parts air to one part fuel." You can find that at the beginning of their article (help.summit racing.com/app/answers/detail/a_id/5230/~/engine-basics---air%2Ffuel-mixture). And you can find that in a lot of articles, books, manuals, etc. I hope that since 1976 the U.S Army corrected its training manuals re: how engines work, as I sent a letter to advise their manuals where all stating what AFR was incorrectly. I actually got a formal letter back from the Commander who oversaw all Army training, advising that they researched my claim and found I was correct. He then told me they would correct any subsequent manuals to reflect the correct description of AFR in future prints. Well, knowing how things often go in the Army I bet they are still saying it wrong. I have all but given up trying to correct this misunderstanding as it is so very pervasive. But, with all this really great material being shared in this channel I felt compelled to point out this one relatively important matter. In any event, I thoroughly enjoyed this video, just as I have enjoyed so many the other video in this channel. There is always a lot to learn and I truly appreciate everything you share in your videos, as well as the time you invest in making these videos. I hope you do not feel I am trying to be anything but helpful in addressing my one little pet peeve re: AFR descriptions. Now, if anyone reading this wants to have a little fun, go ahead and run the google text above, then begin read some of the articles, where many of those erroneous statements are made by well known publishers, to see how widespread this misunderstanding is. You are now of a fairly small, but hopefully growing, sector in our industry who has been enlightened on this subject. For those who are as detailed oriented as I may appear to be (I'm not, not really), I say, "Yes, I know that 'hopefully' is not accepted by many folks as being a proper word." Well, not until we were well into the relatively early 20th century. But, it has been used and abused so commonly that it was finally added to English dictionaries. That reminds of a sign I once in Germany while in the Army. "English is spoken here, but American is understood." It just seems like it is a shared memory I felt was somewhat appropriate in the context of all this info I am sharing. Dang, it must be really late as I am now beginning to ramble... Ciao! Gil
if at a certain idle speed ,say for example 500 rpm a vacuum leak happen the computer add fuel to reach 14.7:1 as a result the idle speed become higher say 550 rpm my question is : at this new speed (550 the engine will idle roughly or smoothly?
Matt when I plugged in scan tool three weeks ago long term fuel trim was around 8% short term 16%. Today I checked and the short term fuel trim is 0%. I know my scan tool is basic but I expect the long term might fall with time. Fault codes P170 and P171 are gone. It was the purge valve hose causing the problems. Engine light is off. An example as you explained parts would not fix. Thank you again.
Great explanation. I had the engine management light on intermittantly, car ran great. Plugged in scan tool long term fuel trim was around 8% short term 16%. I tried this a few times watching the live data when someone else was driving. STFT fell to 0% LTFT has not moved yet but I know it takes longer too respond. If I had a small vacuum leak I would have expected the LTFT to fall. I will keep an eye on it. Had code PO1071 for a while but found another code PO170. I erased the codes, engine management light out and so far staying out. Keeping watching your videos, great educational value thank you Matt. I am a great believer in proper diagnosis, your videos give me a much better understanding of what is happening. Incidently I read if the P170 code returns the fault is most likely the car's electronic control module. We shall see.
I had a PO171 error code and a "lean condition on bank 1" on a Pontiac vibe (also matrix, Corolla or some other Toyotas.) The older cars have a problem with the manifold gaskets wearing out and don't have a good "lip." They wear flat and need replacement. The Toyota new gaskets have a solid lip and fixed the issue. Car runs like new again after replacement and cleaning the manifold / tbrottle body.
I've never been so pissed off and so relieved at the same time in my freaking life!!!!! 🤬🤬🤬🤬😂😂😂😂😅😅😅 Well, I now know exactly what I did wrong!! It worked awesome at first, or so I thought!!! 😅😅 You just helped me out soooooooo much, THANK YOU, THANK YOU!!! ~08 scion tc 2azfe ~Clogged cat #1... low funds... yeah, I gutted it. LOVED the sudden change in engine response!! Didn't realize what was happening tho... couple months later: leaking fuel injector into oil... soooo many gaskets and o-rings leaking!! I've drained the oil, new plugs, injectors & valve cover gasket. I've gotta drop the pan & replace the gasket, oil pump reseal, crank seal, was already gonna do my clutch anyway so rear main as well, oil filter housing... good hell. I got learned the VERY painfully expensive and time consuming way!! Valve seals... Probably have burnt valves... hopefully my freaking cylinder head & block isn't warped or worse... LESSON LEARNT. DO. NOT. GUT. CATALYTIC CONVERTER. Should have done a hell of a lot more research, replaced it (with the now much cheaper than this bullshit) header and O2 adapter, had diagnostics ran throughout process and adjusted/tuned accordingly and enjoyed the rewards properly... OMFG. I BROKE MY CAR THINKING I WAS TEMPORARILY PATCHING THE ISSUE!!! HAHAHA send help. Lmao 🤣 THANK YOU for this video but I'm gonna go laugh cry for a bit and then watch part 2.
Hello dear. Thnx indeed . Really helpfulll. Thanks indeed. You are really good. Today i have seen . In a car renault Stft +23% But i have not understood What means -100% in o2 b1 s2 Short term fuel trim in Banc 1 sonsor 2 . Is - 100 % Is it mean . No catalytic or the sensor doest work? Or what is thee problem here. Plz i want a help
,My wallet is getting pretty thin, I love Cars & Trucks , The Money That I wasted over the years, Looking back I have owned 32 Cars & trucks in my life so far ,Now if I could do life over and go Back freshman year at vo tech I think I would have chosen Auto Mechanics Instead of Welding ,Im a Retired Ironworker 36 years , The very last job I did was the steel barrier fence that surrounded ground zero after 9/11 Manhattan ......What a way to go out.. Great video I learned a great deal, My son is working on a 94 ford ranger splash 3.0 53k original miles barn find sat 13 years did complete tuneup coil fuel pump/ filter No Codes the Motor shakes has a Misfire at low Idle you can feel it in the cab, Step on the gas a little it clears up Not much power ?
![Short Term and Long Term Fuel Trims Explained [Easily]](http://i.ytimg.com/vi/IuM53mlOgHs/mqdefault.jpg)
As a computer engineer who fixes my own vehicle, by far this is the first video I have seen on you tube that lives up to the standard of being intellectually stimulating. Well done and thank you for taking the time to explain the nuances and logic in detail. I am subscribing to your channel. 👌🏽
ranjah007 can you make a program that bypasses all this for a. 98 Dakota
Fellow comp engr here! :)
me too
😢😢😢😢😢😢😢😢😢8
😅😅😅😅😅😅😅😅😅😅😅😅😅😅😅😊😊😊😊😅
I’m a non-certified female service tech in my 20’s starting out at a small mom ‘n pop shop. Even though I’m around cars all day and could swap almost anything you could point at it’s been difficult for me to mentally conceptualize how everything ties together or come up with the right approaches to problem solving. Not to mention it’s hard for my bosses to find time to explain things to me and half the time I’m havnt been sure what questions to ask. I’ve been coming home after work to watch your videos oldest to newest (I find the poor video quality to be quite endearing btw haha) and I love the way you describe the basic fundamental rules in a structured and logical path. I have DESPERATELY been needing it!!! It’s been making my day job 10x more engaging and meaningful to me! Everything is more interesting now that I’m starting to understand the genius of design behind it all haha! I am eternally grateful to people like you who give out such valuable information to a public forum. It’s been changing my little corner of life in nothing but positive ways. Hope you see this. Thank you Matt :)
So glad to hear that and I hope this helps you navigate some of the challenges you are sure to find being a female in the industry. I actually have a little helper on some Friday- a 20yr old female tech student who is very similar to you- she is trying to learn the diagnostic concepts as well. I hope both of you cross paths some day!!
Three wires • fuel • spark• gravity • physics.
Get past fuel and spark.
Except physics, gravity and the elements and the computers control over everything.
The big thing is three wires. ⚡️
Old Pablo Tucson, everyone is a boxer or mechanic. Not liking cardboard, I choose mechanics.
First thing I said, “I hate the electric shits”
If…
That’s All There Is. Now I’ve Seen Everything 🔫
Was that slam poetry?
@@SchrodingersBox Some kind of cooking recipe my guess. Not sure what he's making but sounds delicious honestly
Nicely said!
Any aspiring mechanic that wants to make this an occupational life style choice. Watch this video until these consecpts are understood.
FINALLY someone who explains THOROUGHLY and so professionally, that makes understanding the intricates easy. THANK YOU for your videos, your a true car enthusiasts asset. Will stay tuned in to learn more!! YOUR AWESOME!
'If you get this code and you replace the O2 sensor, you're an idiot' This guy is my Spirit Animal.
What an amazing, clear, comprehensive explanation of STFT and LTFT and their relevance to engine performance as well as trouble shooting process. Thank you so much.
All I can say is one outstanding person to describe fuel trims. For about seven years I have been digging for information on fuel trims kind of hard to understand but this just nails it!!!! Such valuable information to have. I just have to make sure that I can retain it. Got to have this for future thank you brother.
he nails his classes. very understandable!!🏁
One of the most informative videos in my opinion with a guy who cares enough to share and explain his knowledge on you tube, whether you're familiar with fuel trim or not this was very helpful at least for me .great effort sir . thank you
You're welcome ;-)
Schrodingers Box
@@johnshaw5001 not sure if you listened but he never said that STFT set a code. Instead, he said STFT is an immediate response to the percentage of fuel that the pcm is adding or retracting...
If, in a given case, STFT has reached 20-25%, meaning pcm is adding 20-25% more fuel to keep the engine running somewhat normally; after a while, this condition is set as the new normal thing to do by the pcm to keep the engine running and the LTFT percentage (The fuel trim percentage noticed after "a while") is set to this 20-25%.
Therefore, now the pcm takes this increase seriously and set a code for the pro to figure out what has caused this anomaly.
Note: if you are a pro, why don't you contradict intelligently with details instead of just denigrating with a sentence in which you claim to be a pro?
Where is your youtube video on this subject? Share your knowledge Mr Pro. If what you must say is not more important than silence then BE QUIET HATER!!
@@johnshaw5001 what would be a fix for P0430 code.
@@SchrodingersBox would you be able to help me out...pretty much figured had a vac leak (06 envoy) ..when warm stft is -3/3 and left is 10-12 ranges...when accelerating stft goes up to 5-6 ltft comes down to 7-8... but sometimes the scanner will jump and show stft like 5-6 and ltft will.be 3-4... and when cold and idling the numbers jump around a bit..
Techs/mechanics, electricians, plumbers, etc struggle in their respective trades for lack of knowlege on how things really work. Then comes someone like Matt who by previous trade was a scientist but has the smarts to be competent at almost anything. We in the auto repair trade are fortunate to have his perspective and would do well to take advantage of what he can teach. I have been in the auto repair field since 1977 and just had greater understanding of Fuel Trims since watching this.
He's a badass.
I’ve worked industrial process control related to precision furnace combustion for over 40 years and you’ve explained the fuel system in modern vehicles in a concise and easy to understand manner that surpasses any teaching moment I’ve ever had. Thanks for sharing.
the best ever video regarding fuel trims on the internet no one explain the concept like this
shahab alam zeb you are right .. its best video ..
You are a god! Using what I learned from this video I solved a too lean code in one drive cycle, leading to a failing MAF. Replaced the MAF and am now driving with a smile and without a fault code.
This lesson is opening a whole new world . Thank you
This series is the absolute authority on the matter of Fuel Trims/Advanced Driveability Diagnosis BY FAR -- I've come back to this series countless times in the past three years and they have helped me grasp more on the topic than in the previous 8 years of my career as a tech -- Many thanks sir!
thanks my friend. This video is actually used in several tech schools as part of the curriculum in fact. I think it’s the most important video on the whole channel. probably 80% of all my diagnoses start by using fuel trim.
Found your channel today while browsing for info on my 1998 Pontiac Trans Am WS6 with intermittent hard shifts. I am OEM and technician in the wastewater industry. I have grown weary of so-called professionals throwing parts at my vehicles without proper diagnosis. Hence, I do much of the maintenance and repairs on my vehicles myself. I am certainly not at your level of expertise. However, in diagnosing problems with pump and control systems in my field of expertise, I have to rely on good data. Obtaining good data requires critical thinking. I appreciate your passion for understanding mechanical systems and your persistence to make sure a particular problem is properly diagnosed. Thank you for sharing your knowledge. I also enjoyed your video of diagnosing the exhaust restriction for an older lady. I am glad to know there are others like me who share old school values such as not charging for work that was of no benefit or value to the customer.
You are a monster. Such clear and nice teaching. Greetings from Brazil
+Carlos César Machado Lol a monster! I like it!!
+Schrodingers Box your an idiot, i have been an ASE master tech and GM world class tech for a little more than 20 years and diag cars with fuel trim issues on a daily basis and no way does a MAF fuel trim get worse with higher rpms. I will show you my credentials, lets see yours. Quit spouting off shit that you have no clue about, well the rest you were right about but you are honestly totally wrong about MAF fuel trims getting worse with higher rpms.
troopbd I dont have to call you an idiot- you're doing it yourself,.
Show me ONE case study where a vacuum leak got WORSE fuel trim under load and better under idle OR even one case study where a dirty MAF showed normal fuel trims under load but higher at idle and I'll publically aplogize.
If you don't do that I'll just delete you from this channel- or better yet, delete your comments and leave the ones that just make you look like an idiot.
GO! Time is wasting!
+Schrodingers Box wait till I get off work, at the dealership, and I will pdf numerous ones and send them to you.
troopbd CAN'T WAIT!!! I'll cover it in my next video with your comments!!
This was EXTREMELY helpful for me, one that has not even unwrapped my new scanner. I took tons of notes. I have an Explorer that runs really rough and it's burning tons of fuel. I am about to watch Part 2 and then I will begin my interrogation in the morning. My only complaint is that you did not provide your name. Your art skills are just fine. Thank you again sir.
just call him the Fuel trim Whisperer...................
Thanks for the information, I’m finally digesting this after a few years.
This video is more the Brain at heart. I love intelligence and the graphics of discussions, 100%
I totally understand it !!!
I learned. I’m an Idiot
And reclaimed myself to fix my vehicle by watching this video which I should of watched this before I was an idiot
Thank you for the excellent fantastic video
This video definitely helped me understand the difference between lean and rich . The content was very informative and clearly outlines possible scenarios that might trigger these symptoms.
Wow, I'm glad I came across your videos and I can't even thank you enough for sharing the knowledge about all this. I'm knew to working on cars and one of the things I like to do is understanding why things fail as opposed to just replacing things. This is the best video I've seen in regards Fuel Trim, something I knew very little about but the way you explain it in your video makes it very simple to understand. Thanks a lot my friend.
This is sooo helpful! I'm learning fuel trims for the first time in school and it can be kind of confusing but you do a great job of explaining it clearly. You'd be awesome to have as an instructor. Thanks so much!
Best teaching thankyou a lot.
I have 2005 4.8 vortec .
I fund 2 code
P0301
P0171,
Fuel treams was
LONGFT1 0.25
Shortft1 0.0
i didn't change o2sensor .
I check than i found the broken vacuum tube which is located on the top rear right side of engine goes to purge.
I replaced the 3" rubber vacuum tube than 0171 code erased.
For p0301 , i test coil and spark plug and wires , they working good.
Than i pulled out first cylinder injektor it was realy dirty than using carb.cleaner and c c intake cleaner applyng 45ps air into injektor all the dirts come out.
After installing back injektor .
P0301 code also cleared.
Engine runs Smooth and burns lees fuel.
When helping my fellow car owners, i guess because I am a female and I shouldn't care about any of this, I'm not expected to understand this. My problem is I have to fix my own cars. My mother only has me. This has changed my life and made me a mechanic, rather than a me_can lol. Thank you for your time and understanding.
LMAO !!! Matt : "If we have these conditions and you put an O2 sensor in it...you're an idiot"
Hahaha, maybe sounded harsh but it is absolutely 100% true!!!
Not harsh at all, my friend. Thanks for all you do.
You forgot the comma before the word and .
I feel like my IQ doubled from one to two. Thanks for the vid :D
Hahahahaha. I know how yhou feel! Mine doubled from 1 to 3!!! Wait.....
I did learn and understand a little bit more today!!!!….
This is one of those video's where you realize that it's not about a fancy whiteboard or how big it is. This is a video where you realize that it's all about COMMUNICATION!
Thanks you sir always understand your videos appreciate your good work
I can't get enough of all this information... thank you so much for all the great help
Wow, I found this very helpful and wanted to give this guy a long THANK YOU for his energy and passion, but I see that other people have done this in great detail ...so I gave a quick thumbs up.
Thank you so much for making this video!!!! After 2 days of head scratching, I was finally able to pinpoint my problem to a clogged cat once understanding how to interpret fuel trim data and correlate to O2 readings. Your videos have greatly enhanced my diagnostic abilities. Many many thanks!
very valuable information. Thx
Great video and I’m definitely going to continue the series! I even wrote down notes to refer back to while I got my scanner tool out. Thanks!
That is awesome!
Matt: I'm sorry this is so long, but I hope you find it interesting. Your video provided a rational and super-helpful guide for me to follow in trying to diagnose a problem with high fuel trim at idle. (Fuel trims 20%+ at idle, improving at higher RPMs.) Following what you explain in your video, I came up with the hypothesis that I probably had an intake vacuum leak. After much testing though I had to conclude there was no vacuum leak. Testing also showed I didn't have a fuel delivery problem - no problem with fuel pressure, injectors, O2 sensors, exhaust leak, exhaust restriction, leaking cold start air enrichment device. I cleaned the MAF, tested MAF voltage at various RPM/load settings and checked the MAF wiring harness/grounds. All tested normal. The only unusual finding appeared when I compared fuel trim against MAF grams/second output on a scan tool. At steady idle, the MAF grams per second reading was varying by as much as a gram, and the lowest grams per second readings and highest fuel trims numbers seemed to coincide. Eventually I had to consider the hypothesis that the MAF was underreporting idle air flow to the ECU. I found this article very helpful: www.motor.com/article.asp?article_ID=839. The author concludes the article by saying, “If you can't locate a fuel or air delivery problem to explain high or low fuel trim values, don't overlook incorrect MAF...input values.”
Cleaning the MAF with CRC MAF cleaner made no difference. But after I replaced the MAF sensor the fuel trims returned to normal. (LTFT Now 0% with STFT +/- 5% at idle). The grams per second reported from the MAF at idle now varies across a more narrow band, and never falls below 3.5 g/s. (With the bad MAF it was falling as low as 2.8 g/s.) Replacing the MAF fixed the problem.
I decided that replacing the MAF was a reasonable thing to do, even though my testing hadn't absolutely proven 100% that the MAF was bad. Replacing the part seemed prudent, but seemed to fall short of the standard of empirical/scientific justifiability you have set. I guess you could say that replacing the MAF was itself the empirical test that proved the MAF was bad. But that kind of thinking seems like a slippery slope that could lead to becoming a mindless parts replacer. What other tests could I have done to test the MAF before I replaced it? The voltage tests I found in the Factory Workshop Manual and in Paul Danner's book suggested that the MAF was fine. I spent a lot of time testing and ruling out hypotheses related to vacuum leaks and fuel delivery and I was running out of patience.
Even though I thought it was a reasonable thing to do, before I could bring myself to replace the MAF, I had to overcome a psychological hurdle: Namely the sound of your voice in my head saying, “If you replace the MAF, you're an idiot!” As much as I want to be a member of “the 2%” and not “a mindless parts replacer” I guess sometimes practicality demands a lesser standard.
I think the theme of “I want to be a member of the 2% and everybody else is an idiot” has great rhetorical appeal and gives your videos an enjoyable dramatic character. You might find this interesting to read. It comes from a summary of the theory of drama elaborated by the great American philosopher and literary critic Kenneth Burke. He says that all successful dramatic narratives include a victimage or scapegoating mechanism: “Victimage is the process of scapegoating. Here, the speaker blames an external source for his ills. According to Burke, there are two different types of scapegoating, universal and factional. In universal scapegoating, the speaker blames everyone for the problem, so the audience associates and even feels sorry for the victim, because it includes themselves. In fractional scapegoating, the speaker blames a specific group or a specific person for their problems. This creates a division within the audience. The victim, whoever it may be, is vilified, or made up to violate the ideals of social order, like normalcy or decency. As a result, people who take action against the villains become heroized because they are confronting evil.” (from wikipedia en.wikipedia.org/wiki/Dramatism)
The dramatic narrative you've constructed in your videos is an example of fractional scapegoating: it is the mindless parts replacers who are the villains, and it is us - the tiny minority of scientists - who are heorized because we are confronting their stupidity. This isn't a criticism by the way. Burke's claim is that all dramatic narratives work this way. And your video was invaluable in providing me with a strategy to follow in forming and testing hypotheses. But eventually, in the process of finally fixing the car, I also had to - temporarily I hope - embrace the role of idiot.
David UM1996
Two years on and still making people smile, great post. ☺
Thank you for sharing your experience.
I'm working on a 97 Ford Ranger 2.3. I had been noticing sort of poor gas mileage for months; then got a check engine light. Scan tool showed a potential problem with the charcoal canister purge valve. Not interested in empirical testing when I can just grab the part off another rig (But, like you said. That's an empirical test too.)
Since I was right there with the scan tool, I pulled up my fuel trims and noticed right away that I had long term over 20, though it would drop under load. Back home; I checked for vacuum leaks and came up with squat. I watched this video a year or two ago, and thought I'd watch it again, to see if my memory of fuel trims was faulty. But first I scrolled down through the comments.
Your comment about hearing his voice calling you an idiot, or otherwise denigrating you is almost always on my mind when working on a car, and it's saved me some pointless part replacing since I discovered this channel. I just thought it was funny, how we were in just about exactly the same frame of mind.
My wife walked in and asked if I fixed my truck; and I told her: "Maybe. At least what I thought was a problem. But my fuel trim's really high; and I don't seem to have any vacuum leaks. Which is about all I can think of that would cause it... but I guess a bad MAF could do it too..."
And here's your comment. Same problem as mine. (apparently) I've been suspicious of my MAF for quite a while now, and I'm thinking that's probably where I should be looking next.
Joe Sevy
I far from being a ace mechanic but would it set a code for the maf ? I’m dealing with a code on a gm p1174 just wondering if it’s bad gas ? I also think the plugs which are iridium but there at 116000 and I know that it’s need to be changed and go from there .. check for leaks .. there all saying you got change all your injectors and get reprogram not so fast .. the car starts on a dime took on the highway with good response to throttle.. any inputs thanks
@@anthonypapaleo1940 You're really talking to the wrong guy here for that particular code especially! However; I can't see any possible logic in suspecting the MAF in this problem. The MAF detects total air flow to the engine; it doesn't have anything to do with the detection of a rich/lean imbalance between cylinders. The MAF can be, good, bad, or ugly without giving that code. If you're using a non oem air filter especially, I can certainly recommend cleaning the MAF with MAF cleaner, and after that many miles it's probably taken a bit of a beating. But, obviously, your only legitimate reason for changing it at this point is the same one that applies to changing the plugs. As (expensive) maintenance rather than waiting for it to fail. But, I'd be shocked to find that it had anything to do with your situation.
If your plugs have 116,000 on them, I'd suppose they're about due for a change, but I certainly wouldn't have much hope for that to solve the problem as there'd most likely be a misfire p0300 code along with with the p1174. Though I can tell you that I've changed plugs with 144,000 miles on them that were obviously in really bad shape without ever throwing a code. So, if you try it and it helps: Yay! Just don't expect much.
"Bad gas"? I suppose it's possible, but not too likely from what I can find out. I'm rather skeptical about something getting sucked out of the tank and past the filter being bad enough to mess with the injectors, but only enough to cause this code. Though, it's entirely possible for the filter to be clogged badly enough to interfere with fuel pressure; again. I'd expect another code, p0174 and poor performance. Though your code is associated with injector problems; injector problems are also associated with engine idle and power problems. Since you don't have idle or power problems, as far as you can tell, I don't think you're too likely to get anywhere there either. Still, you're the one who feeds it gas. If YOU think you've been giving it bad gas, start giving it good gas. If it sits for long periods of time, then good gas could have gone bad. But again. The whole engine gets the same gas. You're looking at an imbalance between the cylinders. Go ahead and use gas additives if you want. Some swear by them, some at them. My opinion is they sometimes do some good, and I've not seem them do any harm. Just don't expect it to fix the problem.
I'm also rather skeptical, for the same reasons, that one or more of your injectors has a problem, sufficient to cause this code, yet not bad enough to throw another code or cause problems with idle or performance. There's no way I'd even think about putting a set of injectors in it unless that's something I was already considering for some other reason. You can do a simple test yourself on the injectors to look for obvious potential problems. Simply disconnect the electrical connector to each injector and check the resistance of each one. If none of them are greatly different from the others, they're unlikely to behave differently when they receive a signal from the ecu. This may be a lousy way to diagnose injectors, but I've done it successfully before. The problem is that this can only find one possible problem. The injector could well be damaged, perhaps enough to cause your problem, without this test telling you anything. But, it's something you CAN do, and it WILL eliminate one possibility. You can also check the voltage being supplied to the injectors, but I'd expect that to show up as a code as well if it were the problem, and if it were a fault in the wire I'd expect the injector to completely fail, again, throwing a code.
I'd much more expect the problem to be one with an intake leak of some sort, which can be very tricky to track down. You'd suppose a leak would automatically be worse at idle than at cruising speed, but that's not always the case. Finding a leak that only presents itself at speed is going to be quite a problem. Still, that's where to start. Change the plugs, because it's time; then start checking for leaks. If you find one; that's something that needs fixed at the very least; and a very likely cause of your problems. Another symptom of a vacuum leak is if the engine races at startup. If your engine, when started, revs to a significantly higher rpm when started than it used to, or than other similar engines do; you've likely got a vacuum leak.
Since all the likely causes other than vacuum leak or general engine deterioration usually cause idle or performance issues, and you're not reporting any idle or performance issues, and there're no other codes, I really doubt that you're going to get anywhere with the injectors or fuel system. The most likely culprit is going to be a manifold leak of some sort.
If you have some kind of scanner that can show you fuel trims in real time, I'd expect long term fuel trim to be somewhat high if you have a small vacuum leak, anything over 10 and I'd almost guarantee there's a leak. If you don't have a scanner of any sort I'd recommend getting a cheap BAFX bluetooth scanner; buying the Torque Pro app, and using that until you can get something better. I can't make any recommendation for what that better scanner would be because I can't make up my mind what scanner I'd get even if I could get anything I want. But, even if you can't tell the engine's getting more fuel when you use propane, starter fluid, or whatever to find your leak; your ecm can, and it will change the fuel trim to compensate. That's why you need to be able to monitor the fuel trim as you're looking for your leak.
So, what help have I been? Not much. The problem with so much of this stuff is that it gives us problems that are only problems because we're informed about them. If not for this code, you literally wouldn't have a problem to fix. Or at least that's the way it sounds to me. Or, maybe it just gives us the opportunity to fix a small problem before it gets to be more serious.
Hopefully I haven't just added my ignorance to yours. Hope you fix your problem!
Joe Sevy
Thanks joe my idol seems a little choppy but not bad but not racing .. also this code came up after my wife fill up at this one station.. so I’m taking the car to have the plugs changed , maf clean , throttle body clean ... I really don’t know what was done this car I just bought three months ago and also do my own maintenance but do the cold here in Chicago and no garage ... But like I said this only code I get no miss firing or any other code .. I really don’t like throwing parts at and till I know for sure . I will have the shop run a scan and see what’s up with .. thanks for any suggestions...
Hands down the best explanation I’ve ever seen on 02 sensor voltage telling short and long term trims what they need to do for the perfect 14.7-1 AFR. Can’t wait to to watch part two. Very useful information, thank you!
Thanks 👍
I am feeling like I am at a univeristy. So much information and its very accurate and usefull.
THIS IS GOLD!! Thank You for sharing this useful informations. My car runs bad when cold and I taught that mabe its the O2 sensor. But I found out that it doesnt work when cold. Next I will check MAP, throttle body and fuel pressure regulator. I changed the ECT sensor so tomorrow morning I will see if I figure it out.
Thanks for straight foreword teaching- and Not having a darn music/fancy/dumb introduction.
2019 and still good advice from the day it was made. Im new to Fuel trim but understand it all so far AWESOME. Onto part 2...
I love your video good info 😄 keep it up I keep looking
“Brilliant” Thank you.
Awesome video man, very well explained ! I wish other mechanics would watch. I got a p015b code on my 5.3l v8 with a rough idle. I took it it to a mechanic today and the first words where "02 sensor" ... my next words where "your an idiot " bye😂
27:42 of pure genius instruction! This convinced me to subscribe! I hope you are instructing at a top-level school, you should be!
Awesome video keep them coming very well explained and informative.
Ball Out til you Fall out! Much more to come... much more!!
Can't thank you enough for making this and your other videos. I learned to wrench on cars back when they had oil bath air cleaners so understanding the PCM has been a real challenge for me. Your videos break down how they work in an understandable way so I can troubleshoot to compotent level and not just guess what part to swap out. Keep up the great work, you are an awsome teacher. Thank You.
Great video!! Thank you so much. I had a check engine light on my 2000 Silverado. Both PO171 and PO174. Hooked my scan tool and checked the short and long term fuel trim. Found the long term steady above 20 percent. Took a closer look and found a vacuum hose had come off. Plugged the hose in and no more light. You saved me a couple hundred and I really appreciate it. Thanks so much!!
John Webb great
Thank you so much for sharing all this knowledge. I'm learning so much.
glad to hear it!!
YOU ARE A LEGEND SIR
Thanks!!
Well, Ive either been to idiots or scam artists. I've had the O2 sensor replaced, intake manifold, MAF sensor (2x) once I replaced myself and the second time the mechanic did it and charged me $400 for a 10 minute job, replaced the fuel pump, and on and on. Thousands of dollars later I still have the problem. Thank you for this video. You explain things very well for those of us that are novice auto DIYers. I think I'll be my own mechanic from now on. :)
You make this so easy to understand ..Much appreciated.
Amazing video. Thank you so much! I never leave comments on videos, but in your case you totally deserve it. Keep up the good job!
Watched again. I have a V6 engine. I've got 2 air fuel regulators, 2 cats, and 4 O2 sensors with one exhaust.
Going to check the manual again to be sure, I don't think it even covers this.
My 2013 chevy Equinox 2.4 lt show rich B1-S1 and the eng. Died code P2A00?
now you can easily diagnose it!!
I just 'Feel the love' Everytime UA-cam brings me to this channel from the host... Ty
Hey man, I really want to thank you for your time and your talent explaining this to another mechanic, it’s not over simplified yet you’ve put everything into a much clearer perspective and probably made me a much faster worker. Thank you very much for that, to me there was always a little confusion in how to utilize STFT and LTFT in a proper diagnosis but now i see how and why it’s important.
Thank you for doing this. I have been DIYing my cars for a long time and this kind of stuff would have been very helpful back when I started.
Mate! You do good, in a few minutes I understand what the STFT & LTFT means and how it works
You are very good mate at explaining
Thanks Great Video For Me Salute to You Sir
I am restoring 1988 corvette. I have been told there are no scan tools available for it. Do you know of any that would do the job
I do not. on OBD1 I just draw the codes using a paper clip and then manually test the systems.
This video was made back when the internet didnt suck and wasnt lousy with idiots making 'reaction' videos.
Hahahahaha. Amen brother!!! Totally with you on that!!
great video tk for share you knowledge
Very awesome, i subscribed to ur channel keep teaching me!
Very inteligently expaining! Good job man!
I want to master this!!!
---and then I want to autozone,,,,,,,
Great video. Thank you for sharing your knowledge with the community. I appreciate the thoughtful and logical way that you approach engine problems.
You remind me so much of my son. Unbelievable! He explains computers to people just as you explain the workings of the engine. Same mannerisms and speaking style....Anyway, he's over 2000 miles away which is okay because I wouldn't want him to see his father going crazy over this 93 Chevy 1500 with a 4.3, and which I've changed every sensor and at my wit's end. I'm trying to watch all of your videos and taking what I can use I'm putting the rest aside. I'm not going to give up. I'm not a quitter. But I lay awake at night wondering if there was something I might have missed. That it seems I end up making it worse. It's a good little truck and I want to keep it. But most of all I need to figure it's out. Surging at idle. Misfiring at low idle and up to maybe 30 miles per hour. At higher speeds it feels like I'm pulling somebody with a rubber band but the engine sounds better. Sorry. I'm rambling. Thank you for the videos. Hopefully I'll combine them and get my truck back on the road.
Well if you can get me some numbers i can probably help. It all starts with fuel trim and then you know where to start your diagnosis.
@@SchrodingersBox unfortunately it's OBD1 and I don't have a scanner. I'm well adapt at troubleshooting with a voltmeter and basic electronics, so that's what I'm working with, in accordance to your videos in which you apply the voltmeter.
Getting the 5 volts at the appropriate sensors, ran the TPS up and down, slowly and smoothly. Results were excellent.
Against one of your cardinal rules, and having quite a bit of "reward points" at AutoZone, I replaced the oxygen sensor, IAC, TPS, EGR valve and the solenoid, ignition control module, and tested the primary and secondary on the ignition coil. (Low and high) and resistance was well within the specs. Testing with a vacuum pump I found no vacuum leaks. Getting some excess oil on the spark plug threads so replacing the valve cover gaskets now even though they look fine. I am getting terrible fuel mileage. No excess smoke from the exhaust, but has fairly strong order of unspent fuel.
I've succumbed to the fact that this is my purpose in life. My mission from God. I'm on a quest to figure out what's the matter with this truck!!!! Lol
Of course I'm kidding... but like you, I'm not satisfied with taking it to a dealer and have them them fix it. I need to do with myself and understand what the issue is and, more importantly, WHY the issue is. Lastly, I have a one way airflow valve ordered to make my own compression tester. I could buy one, but using the time 2 troubleshoot all the other things. Compression check should have probably been the first thing to do in case I'm wasting my time. But I'm enjoying this even though it's frustrating. If that makes sense. 🤔 I understand it's difficult if not impossible to diagnose a vehicle when you don't have your hands on it. Thanks for replying and if there's any other pertinent information you'd like, I'll do my best. Hope my book didn't put you to sleep. 😴Thanks again.
P.S. I did the jumper thing between the A and B on the OBD1 Outlet to get the flashing codes. The EGR 13 is the only one I've ever gotten. Currently, there is no check engine light but the thing runs terrible. Especially at idle and just "getting going". Seems to correct itself at higher speeds except for that feeling of pulling something with a bungee cord or rubber band.
Thank you Sir. This was a very helpful and has helped me diagnose a very long and painful problem with my Honda Civic.
So many questions....Who is he talking to? Is Stoichiometry contagious? Who is making all of these fuel adjustments, a small squirrel with a screwdriver in the carburetor? Is this real life....? Is he tripping he looks like he is wired?
And the most important one- can you now use basic fuel trim analysis on performance dignosis?
johny you really need to get a life..............
Great explanation. Thanks
Man you are a GOOD teacher! I’ve been trying to understand this for like 3 years.
You are a dream come true thanks for the video
I feel so much smarter!! 👨🏫
That was awesome!! Thank you!
Wow, wow! super informative. Your explanation is clear and understandable. I wish i had learned this before my mechanic asked me to replace a host of sensors.
This is exactly what I was trying to learn. THANK YOU
I'm looking forward to plugging in and checking my stats! :-) Thanks for taking the time to do this.
I just can't Express how great this video was for me a least
A Hello to Ms Vikki and the Cat. 🙂
( Should it happen that the Cat is alive)
It is alive!! And dead!!
Thank you soo much for the info, give a man a fish or teach em how to fish makes a difference, thanks this stuff is always tough figuring out!
Thanks to your video I was able to figure out the problem with my car , Stft and Ltft 18% at idle but Ltft would drop at higher rpms but Sftf would not move even at higher rpms.
, I tested fuel pressure was good, it turned out it was the fuel injectors, thank you very much!
Incredibly good. Viewers, show this man some love and thumbs-up other comments, it helps the algorithm immensely for him!
Thankful i came across your channel, very informative and easy to follow. Was able to diagnose and fix a P0171 on a 2014 Nissan Pathfinder using the LTFT/STFT readings. Have to admit i had to fight my instincts/desire to gravitate to the sensors (MAF/02) as the source of the problem but i trusted the method and more importantly the "data". The data showed higher fuel trims at idle and improved (lowered) at higher RPMs. Started hunting for a vacuum leak and low and behold a bad crankcase breather hose (in the worst spot in the engine compartment) was the culprit. $7 bucks later and the fuel trims are headed in the right direction (just need to let it get to the new baseline and should be good). Thanks again!
Well done! The data will tell you problem if you let it. As you said, most people will just jump to a conclusion rather than interpret a conclusion.
Did that cause any driveabilty issues for u?
Was a while ago now so do not exactly recall all the details but I do not recall any drivability issues. Think it was just the check engine light and maybe some reduced gas mileage that sent me hunting for the problem.
Thank you for the fuel trim explanation I have gone though all the tutorials on UA-cam and your explained it perfectly just as the computer reading 14.7.1 ratio. As for the people who dint agree with your tutorial the saying goes We Agree To Disagree. your work is appreciated.
Good job! you just helped me to figure out a vacuum/boost leak on my WRX! Thanks!
Taken on a 175km trip now all looks good (touch wood) STFT around -1.6 Banks 1 and 2
LTFT around -7 Banks 1 and 2 and motor seems to be running smoother. Next I will check Fuel consumption Thanks for your help. Over here in Australia most of the mechanics I have spoken to about this problem just tell me to just reset the codes, this has made my head hurt for many years, my fingers are crossed.
Graeme in OZ
Not trying to be a jerk, sincerely. But... There is a very wide spread misunderstanding of what a 14.7:1 Air:Fuel Ratio (AFR) means. It is often stated as a ratio of 14.7 parts of air for every 1 part of fuel. That is incorrect. And I have come across this error in factory training, discussions, classes, manuals, and even military training manuals involving emission control and fuel systems for engines.
The correct way to state the 14.7:1 AFR is there are 14.7 pounds of air for every pound of fuel, or even more correctly in a 14.7 AFR the mass of air is 14.7 times the mass of fuel (weight and mass are related, but for the purposes of my comment I feel the use of a unit of weight vs using the word "mass" makes it clear what AFR really means). In short, for clarification, an AFR is a not volumetric measure based comparison between air and fuel. If you think about this for a moment you will realize that if it was a 14.7 parts of air for every 1 part of air, we would be seeing far less air being pulled into an engine. There are other implications that further point out the folly of a volumetric based ratio involving air when it comes to the density of air molecules for any specific volume at various temperatures and/or altitudes.
There are other units of weight that are used as opposed to pounds, but despite the unit of weight used the ratios of the weight of air compared to the weight of fuel remains unchanged. Accordingly, it is also correct to say the 14.7:1Air:Fuel ratio is also described as being 14.7 grams of fuel for every 1 gram of fuel.
For anyone who doubts that I am speaking accurately, please Google the following text, then read what Wikipedia says.
WHAT DOES A 14.7:1 AIR FUEL RATIO MEAN WIKI
As far as how widespread the incorrect description is, one only needs to drop "WIKI" from the Google search string above, then begin to read some of the descriptions, such as this one from Summit Racing, where they say in an article named, "Engine Basics - Air/Fuel Mixture," the following, "AFR stands for air to fuel ratio. Fuel doesn't burn on its own. It has to be mixed with air. AFR tells you how many parts of air are mixed with each part of fuel. For example, a 14.7:1 AFR (or just 14.7) means the mixture is 14.7 parts air to one part fuel."
You can find that at the beginning of their article (help.summit racing.com/app/answers/detail/a_id/5230/~/engine-basics---air%2Ffuel-mixture). And you can find that in a lot of articles, books, manuals, etc. I hope that since 1976 the U.S Army corrected its training manuals re: how engines work, as I sent a letter to advise their manuals where all stating what AFR was incorrectly. I actually got a formal letter back from the Commander who oversaw all Army training, advising that they researched my claim and found I was correct. He then told me they would correct any subsequent manuals to reflect the correct description of AFR in future prints. Well, knowing how things often go in the Army I bet they are still saying it wrong. I have all but given up trying to correct this misunderstanding as it is so very pervasive. But, with all this really great material being shared in this channel I felt compelled to point out this one relatively important matter.
In any event, I thoroughly enjoyed this video, just as I have enjoyed so many the other video in this channel. There is always a lot to learn and I truly appreciate everything you share in your videos, as well as the time you invest in making these videos. I hope you do not feel I am trying to be anything but helpful in addressing my one little pet peeve re: AFR descriptions.
Now, if anyone reading this wants to have a little fun, go ahead and run the google text above, then begin read some of the articles, where many of those erroneous statements are made by well known publishers, to see how widespread this misunderstanding is. You are now of a fairly small, but hopefully growing, sector in our industry who has been enlightened on this subject. For those who are as detailed oriented as I may appear to be (I'm not, not really), I say, "Yes, I know that 'hopefully' is not accepted by many folks as being a proper word." Well, not until we were well into the relatively early 20th century. But, it has been used and abused so commonly that it was finally added to English dictionaries. That reminds of a sign I once in Germany while in the Army. "English is spoken here, but American is understood." It just seems like it is a shared memory I felt was somewhat appropriate in the context of all this info I am sharing. Dang, it must be really late as I am now beginning to ramble...
Ciao!
Gil
Profoundly informative video. Didn't know what I didn't know. Many thanks
if at a certain idle speed ,say for example 500 rpm a vacuum leak happen the computer add fuel to reach 14.7:1
as a result the idle speed become higher say 550 rpm
my question is : at this new speed (550
the engine will idle roughly or smoothly?
E X C E L L E N T video!!! Very understandable...Thanks.
but the autozone guy told me to get new oxygen sensor, so is he the idiot? or me? or both of us??
it depends. what was the data indicating?
Matt when I plugged in scan tool three weeks ago long term fuel trim was around 8% short term 16%. Today I checked and the short term fuel trim is 0%. I know my scan tool is basic but I expect the long term might fall with time. Fault codes P170 and P171 are gone. It was the purge valve hose causing the problems. Engine light is off. An example as you explained parts would not fix. Thank you again.
Wow ... your a good teacher keep up the good work...
Great explanation. I had the engine management light on intermittantly, car ran great. Plugged in scan tool long term fuel trim was around 8% short term 16%. I tried this a few times watching the live data when someone else was driving. STFT fell to 0% LTFT has not moved yet but I know it takes longer too respond. If I had a small vacuum leak I would have expected the LTFT to fall. I will keep an eye on it. Had code PO1071 for a while but found another code PO170. I erased the codes, engine management light out and so far staying out. Keeping watching your videos, great educational value thank you Matt. I am a great believer in proper diagnosis, your videos give me a much better understanding of what is happening. Incidently I read if the P170 code returns the fault is most likely the car's electronic control module. We shall see.
Thank You Very Very Much For The Information And You Are Such A Great Teacher, Thank You Again.
have a e92 corolla have electrical problem from relea..to and lot of bypass wires need wire digra...ect to start the car
need as much info..avaible on this car
bbbindustries.com
I had a PO171 error code and a "lean condition on bank 1" on a Pontiac vibe (also matrix, Corolla or some other Toyotas.)
The older cars have a problem with the manifold gaskets wearing out and don't have a good "lip."
They wear flat and need replacement.
The Toyota new gaskets have a solid lip and fixed the issue.
Car runs like new again after replacement and cleaning the manifold / tbrottle body.
I've never been so pissed off and so relieved at the same time in my freaking life!!!!! 🤬🤬🤬🤬😂😂😂😂😅😅😅
Well, I now know exactly what I did wrong!! It worked awesome at first, or so I thought!!! 😅😅 You just helped me out soooooooo much, THANK YOU, THANK YOU!!!
~08 scion tc 2azfe ~Clogged cat #1... low funds... yeah, I gutted it. LOVED the sudden change in engine response!! Didn't realize what was happening tho... couple months later: leaking fuel injector into oil... soooo many gaskets and o-rings leaking!! I've drained the oil, new plugs, injectors & valve cover gasket. I've gotta drop the pan & replace the gasket, oil pump reseal, crank seal, was already gonna do my clutch anyway so rear main as well, oil filter housing... good hell. I got learned the VERY painfully expensive and time consuming way!! Valve seals... Probably have burnt valves... hopefully my freaking cylinder head & block isn't warped or worse... LESSON LEARNT. DO. NOT. GUT. CATALYTIC CONVERTER. Should have done a hell of a lot more research, replaced it (with the now much cheaper than this bullshit) header and O2 adapter, had diagnostics ran throughout process and adjusted/tuned accordingly and enjoyed the rewards properly... OMFG. I BROKE MY CAR THINKING I WAS TEMPORARILY PATCHING THE ISSUE!!! HAHAHA send help. Lmao 🤣 THANK YOU for this video but I'm gonna go laugh cry for a bit and then watch part 2.
Hello dear. Thnx indeed . Really helpfulll. Thanks indeed. You are really good.
Today i have seen . In a car renault
Stft +23%
But i have not understood
What means
-100% in o2 b1 s2
Short term fuel trim in
Banc 1 sonsor 2 . Is - 100 %
Is it mean . No catalytic or the sensor doest work?
Or what is thee problem here.
Plz i want a help
,My wallet is getting pretty thin, I love Cars & Trucks , The Money That I wasted over the years, Looking back I have owned 32 Cars & trucks in my life so far ,Now if I could do life over and go Back freshman year at vo tech I think I would have chosen Auto Mechanics Instead of Welding ,Im a Retired Ironworker 36 years , The very last job I did was the steel barrier fence that surrounded ground zero after 9/11 Manhattan ......What a way to go out.. Great video I learned a great deal, My son is working on a 94 ford ranger splash 3.0 53k original miles barn find sat 13 years did complete tuneup coil fuel pump/ filter No Codes the Motor shakes has a Misfire at low Idle you can feel it in the cab, Step on the gas a little it clears up Not much power ?