Diagnosis and Understanding: MAF Sensor Pt3 - Diagnostic Procedures
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- Опубліковано 10 лип 2015
- In the final part of this series we look at common MAF problems and how to diagnose them- or more specifically, how to not misdiagnose them!!
Part 1 of this series is here: • Diagnosis and Understa... - Авто та транспорт
I spent 35 years in the nuclear industry. Your instruction is on par with my training. I am impressed with your instruction and clear explinations. Thank you.
Good to know! I like being fact checked- keeps me honest!!
Found your video while browsing as I am an auto diagnostic technician and have paid much money on courses to learn what I do now I found I learnt more from your video than the courses. You should teach this to techs in the workshop you would earn a fortune. Thank so much for such a brilliant informative video lessons totally brilliant 👍👍👍👍👍👍👍
So true
Thanks for the videos it really helps me a lot. Sometimes I watch the same video multiple time to make sure I get it right. The knowledge is actually sinking in! Thanks again.
Excellent series here! I have Paul Danner's book and have worked my way through it while watching his paid channel. However, I must admit it has been your approach and your videos that have "connected the dots" with my understanding of these systems. I am just a DIY'er, with a passion for auto repair and, thanks to you, I am gaining a much stronger understanding of how to narrow down the list of possible component failures when diagnosing vehicle problems.
Thank you!
Every minute watching your videos worth it thousand of dollars thank you for your time
Man, solid series here. Clear, clear, clear info. Not many youtubers take the moment to review, do a case study, etc. Genius. Just a young backyard mechanic here. Working on turning vehicles around. I've definitely read my fair share of books on other subjects, but the fact that you learned all of this out of a service manual and simply are translating this into more universal techniques for all vehicles. I thank you.
Btw, I'm starting to feel a little cocky now that I've been getting all these multiple choice questions right. I'm just waiting until I make a stupid, jumping-the-gun kind of answer. Because after you correct me you'll say something along the lines of, "If you didn't get that, this is the wrong channel, go back to 4th grade geometry" LOL
Lol- my recommendation is to be confident but not cocky.... but act cocky if you want to quickly grow a UA-cam channel ;-)
Hello Matt, just wanted to thank you one more time for your excellent videos and really really great work sharing all this with us.
***** Thanks John. I enjoy it as much as you guys do.
Just checked an online VW manual, I too have probably been cleaning the I.A.T not the maf wire or vice versa. No codes but sometimes the high idle stays high for an extended period. No vacuum leaks and the temp sensor is fine.
Cheers. Always learn something here.
Matt lovely work as always! Just a wee tip. To speed up work and avoid confusion it is better to use battery ground reference on your scope / DVOM first. I noticed you use sensor ground without wiring diagrams which is fine but can confuse less experience people when they backprobe wrong wires (and get 7V as in your example). Battery ground will just give you less clean signal on some sensors due to noise.
Also it is worth always checking MAF power & ground under load. You would be surprised how much current they can actually draw. Any voltage drop problem will cause inaccurate MAF reading when MAF is clean and sound. Another variable to consider during diagnostics :-)
Yet another great video my friend I have been utilizing your videos for my own knowledge and have also passed them on to some of my coworkers we work on forklifts and most of them are not aware of fuel trim and engine management issues and how to diagnose them
Your videos are great , even years later they still help out .
Thank you so much for all the awesome work you do. I actually did have a bad MAF. I got a cheap scan tool (Bluedriver) which does surprisingly well. Took a look at fuel trims, mass air flow rate, etc. Found that the fuel pressure regulator had to be replaced (diagnosed because I had a little bit of gas leak out of the vacuum port). But still had high fuel trim and my rpms randomly revved up and down. The MAF is a digital not analog and I don't have a scope (too expensive for a beginner). I eliminated everything else that it could have been, went down to the junkyard and tried a maf sensor, worked like a charm. I know it's pretty rare but it does happen. FYI, I had cleaned the maf sensor very very well to rule that out to.
Good work- sounds like a valid scientific process!
How did I miss this channel? I don't fix cars but belong to the 2 percent that want to understand how it works. Getting 1.337 on the MAF test made me subscribe. It was a sign.
Here I am. I am sick of diagnosing silly, vibrating 4cyl engine (no success yet) but even now I've enjoyed your video.
For me it is kind of relax to be here watching you moving the wires LOL
Great, complete story. All about content!
Thanks once more sir, you are the Love of every enthursaite mechanic, we love you so so much
Thank you for your time and willingness to share knowledge. I agree with you and some other premium channels in the effort to educate us diyers to the point of avoiding becoming parts changers. I'm retired from another profession, but my interest in automotive diagnostics really stemmed from dealing with high dollar shops who do that very thing, which is throw parts at a vehicle until maybe it runs correctly. I just finished watching this MAF series after realizing I had watched it a couple years ago, and remembered how enlightening it was. So I hope this puts me in the 1% group. P.S. don't sell your drawing abilities short. I tend to learn by visual inputs, and your whiteboard illustrations are great.
Thank you!!
I love your channel! I take automotive classes, and this helps alot to better understand the electrical aspect of automotive technology.
+Pamela Reid Thanks for the comment!
Thank you so much, I'm graduated from uti, but explained way better than I ever had in the past, thanks again
I have been watching your videos and I have learned so much . Thanks for sharing your knowledge . ...
Excellent series on the MAF sensor.
I had to post a comment to show my appreciation for your in depth and well explained series in these videos. Some great contributions from your followers too. Keep up the videos. I am really enjoying what I am learning from them. Thanks again.
ngl777777 Thanks man,especially on your view of the contributers on this channel. I couldnt agree more- I also learn a ton from the comments as well. In fact one of the best parts of the whole channel is there is very, very minimal "flak" to sift through to see good comments. Most all of them either ask great questions or provide great accuirate information.
Amazing stuff to learn. Thank you.
Thank you for the videos and taking the time to share your knowledge. I appreciate it, and love the videos!
+Brenndon McGill You're welcome!
your vids are very informant and well explained thank you for doing this,and yes im a hard core viewer now,
Thanks for a highly informative video series! You emphasized that any faulty component in the ecosystem (o2 sensor, MAP, throttle, MAF, IAT) can throw a code for any other component in the ecosystem. It would be great if the video also includes more examples of such diagnostics. That said, what would say is the most likely problem when there is a combination of faults between the MAF, IAT and downstream O2 sensors as follow?
- P0102: Mass or Volume Air Flow Circuit Low Input
- P0113: Intake Air Temperature Circuit High Input
- P0420: Catalyst System Efficiency Below Threshold (Bank 1)
- O2 Bank 1 Sensor 2 FAIL
, Max: 100.00641% Min: 19.99823% Test result value: 17.37656%
- O2 Bank 2 Sensor 2
FAIL, Max: 100.00641% Min: 39.99799% Test result value: 35.58479%
- O2 Bank 1 Sensor 2 FAIL, Max: 6,553.5S Min: 20S Test result value: 6.6S
- O2 Bank 2 Sensor 2
FAIL, Max: 6,553.5S Min: 20S Test result value: 18.3S
It is very admirable that you ate the cost of that misdiagnosis. you are a stellar human. I've gotten soaked by so many mechanics in my lifetime who made me pay for their mistakes. I'm sorry for my confusing messages yesterday. 3am..heh,heh.... Disconnecting the maf and having it run fine kinda cinched it for me. Plus the wildly erratic data I got on Torque live data. My new Maf works but is over reporting and gives me ltft of -15,which goes away when it is disconnected. Unfortunately parts for my 01 Suzuki xl7 are scarce and cheap aftermarket stuff not so "on fleek". I've ordered another and am hoping. Has it ever been tried inserting a trim pot in the signal line to trim the output voltage down a bit? High current may be an issue for the little trimpot. Thanks for all your efforts, Mat. Very helpful.
Wow excellent information as always . Thank you..
Love the video and your enthusiasm - even when you've just pointed out I should go back and watch some of the more basic videos !! Lol
I am working on a ford. I unplugged the MAF sensor and the condition did in fact get better.
Sir, thank you very much! This video helped me troubleshoot a very challenging lean condition on 2011 4banger Camry, airflow sensor literally was intermittent to the point even the dealership was 100% sure the part was fine, and then it finally completely failed!
Oh wow sounds like a good case!!
Love this series! Would love a turbo electrics series. A lot of the newer cars have turbos as standard on diesels with vnts. Would love to understand how they work to your level of detail
So would I lol!! I have yet to even see a turbo. If I do believe it will be like a Guinea pig for me lol!!
a best giver, a good teacher
awesome series !
13:00 Great point! Note worthy. When people try to modify their cars they often end up making things worse for years prior to learning enough to make it better. The fact that you know this should be reason enough alone for everyone in the automotive world to subscribe to your channel. Schrodingers Box is the real deal. If you aren't subscribed to this channel you're an idiot.
Yeah its hilarious what people on those forums do with the narrow-minded limited comprehension of "more air=power", "colder air =power" and "more fuel=power". Having spent time in those breeding pits of ignorance, it's actually the main reason I gave up on those places and started my own channel. You couldn't fund a single person who didn't chop the MAF, bypass their TB coolant, and relocate their IAT to outside the car.
Schrodingers Box In my circles there are people that delete the IAC, coolant bypass, and put a resistor on the IAT. Yuuuup, check please.
***** last night I saw a video of a guy indexing plugs on a stock civic lol.
Schrodingers Box LMFAO, come on now...
Schrodingers Box Apparently indexing spark plugs is bad...don't know what that would have to do with them being in a car.
Excellent explanations.
@ 12:00, "laminar flow" is the term for the "straightened air" (pretty sure you knew, just mentioning for others).
The "straightened air" can be thought of as "flat layers", or "parallel layers" each riding along on their nearly microscopic individual path, thus making the measurements much more accurate than if it were just a big glob of turbulence, as you mentioned.
This laminar flow is used in many, many areas of science, physics, aerodynamics, manufacturing (clean rooms), etc
douglas lee Yep- we use a "laminar flow hood" for cell culture and other sterile work- the shield of air protect the sample from outside air contamination.
Got an issue with a MAF sensor on my Ford, so I kicked off by searching for videos on MAF sensor testing. What was I thinking? When will I learn that, for proper diagnosis of engine faults, there's really only one guy. Ok, ScannerDanner is good, but this guy takes the biscuit. It almost seems ironic that the best automotive teacher on UA-cam is also the most under-rated. Forget the others, just filter your search results to include only those from Schrödinger's Box.
Your videos are amazing and I am a subscribed user. One comment you said you have almost never found a defective MAF, well I have. I was suspicious of my MAF, before I studied your series, and made the mistake of installing a Chinese made MAF. Gigantic mistake. After watching your series, I reinstall the original MAF, after clean it carefully and all problems disappeared. Great videos, I am a dedicated fan
Thanks for the info!
Ur one of the best teachers out there 😊 thanks
Happy to help!
Thanks man great video as usual .
tkx for the video and advice ... mine hade 3 cold solder connections 12v gnd and iac send ... resolderd them and good to go!
took you awhile to get this out, rough times at work? I'll just put it to watch later cause i'm rushing to work too. Glat to see part 3 out. Have a nice day, keep going Matt!
Big thumbs up and subscribe, loving your work man. Extremely helpful for me.
Glad to hear it!
I doing a small work shop in sri lanka,its very useful these videos to my works
I am glad to hear that!! It seems you are watching every single video hahaha
Thanks man . You are the best .
Thank you so much indeed. What a great video
Thank you for all your videos👍🏼
So nice of you
Excellent video as usual!
Regarding your conclusion on the first part where a guy was probing the wrong wires, if the signal voltage was changing with RPM, it would still indicate a change whether or not he was referencing +12v or ground, since either side would be constant. Think voltage divider. In fact, if you used a scope and placed the ground on the +12v (assuming isolated grounds) the signal displayed would just be a top to bottom inverted view at 7v peak to peak instead of 5 volts peak to peak.
I actually thought you were going to pick number four (the digital MAF) since the signal voltage remained constant with RPM.
Of course, I could be completely nuts.
came here to see this, on a 3-wire MAF with 12v supply, ground, and a 0-5v signal wire, you'd expect the signal to change regardless of where you're measuring.
This an excellent series. I will watch it over and over again. By the way my Klein MM2300 measures up to 500K Hz. auto range. Like you say, when I bought the meter I though, what the hell am I going to do with a Hz. measurement.
+Ed Waggoner Sr. (Papatch) Yes that meter will be ideal for MAF measurements. Also some MAP sensors use frequency as well.
I watched all 3 videos, and utilized them to my advantage. I solved the problem properly and it felt very good. I made a video that I think knocks it out of the ballpark and can help others as well.
I love your videos and I always like how you look for evidence for your conclusions, I always do the same. I had a problem on a BMW e46 with a mass air flow which reads sometimes on the scan tool. Tested the signal wire with it unplugged and ignation on and got 0 volts but when its plugged into the sensor it reads a voltage from about 0.9 to 2 volts when the rpm is from idle to 3000 rpm. At first I was thinking a broken signal wire but when I got a reading when plugged in it had me questioning myself. Any Suggestions? Was thinking maybe its a digital signal and my multimeter is averaging 0.
I love these videos....and your mention of 'maxing out' fuel demand at 2500RPM(for example) is a symptom of my daughters car ATM. I am now one of the 2% (hopefully)
14.7: 1..........
Thanks for your video. after watching, ran out removed wire from maf sensor and car running fine. After a few miles driving i thought (plug it in) while engine running . yes it kills the engine dead.will not restart until removal of wire. new maf ordered.cheers
I don't understand - why would you replace a MAF based on that? That makes no sense.
I'm not too sure but it runs without it connected . so have ordered new maf..all started after refuelling.start car revs up over 2.500 and dies.short story . o2 wire burns on exhaust melts wires past connector. o2 and new loom fitted. car is the odd ball opel zafira 2000 1.8 16v. .their is power up-to maf 12v. Mind you the car runs better than it ever did with it connected .may keep it off :)the water temp gauge is working normal now ?use to be all over up down. stable now.gears smoother.ticks over @800 before was up and down 700 to 1200. test on the maf. . as i have found a ref for it. pin 4 - 12v pins 2-3 ign on 0v pins 2-3 idle 0.6v and pins 2-3 accelerate briefly 4v briefly. mine is 5-6 v on all......cranking..as it wont run when connected....so id say its shot. your videos are a great help .
will let you know results if i put new maf on. thanks.
face vendetta It makes no sense to replace the MAF based on that evidence. You have no frequency or voltage measurements verifying a defect with the MAF.
thank you sir. you are a brilliant technician
Thanks and welcome!
Great info .......waiting for next video
Verry Verry good, I got a lot from this, thanks V much
Woow thank u very much techer i am very like ur video this is agraet school thank u very very much
At 21:29 pure solid gold info. I mean it all is but that one is a real staple.
Hey Matt, I am new to your channel, I am ASE Master technician, and also Automotive Instructor for Antelope Valley College in Lancaster CA. I must say your scientific background and automotive experience is very impressive. Your doing a great job, I think Keep up the good work!
Bruce Shanks Thanks Bruce- it's always very good to get "validation" from the pros such as yourself to ensure the information I put out there is indeed accurate!! I take every effort to make sure I do that.
I just want let you know that you have 100% World Wide validation! best regards from Europe
Great job like always
jess valdez Thanks bro!
jess valdez Agreed. Even as a professional technician I'm learning from your videos. Get a scope already.
Turbotomass I did lol!! See Part 2 of this video series!!
In a future video, can you touch on why a lean fuel mixture is hotter than a rich mixture. It's counter intuitive and your explanation on the matter would be enlightening, considering your scientific approach.
rusco321 I believe you're talking about how the MAF as is it got hotter got more inaccurate when it was dirty?
Since it needed more and more air to react to incoming air, that would mean the O2 sensor would sense a lean mixture.
When a sensor doesn't "see" as much air flow as there really is, the more air flow their is the more off it is.
Since the MAF on my 1999 Chevy Prizm has a combined IAT or Intake Air Temperature sensor, I was able to use a laser guided thermometer to see that my IAT was causing the same problem that Matt was discussing here with the MAF.
This has to do with what is called latent heat of vaporization. When you get out of a swimming pool or shower, you feel cold. This is because the water evaporating off your skin steals your warmth as it is enduring the phase change from liquid to gas. Any time there is a phase change, there is a dramatic amount of heat required from its surroundings for it to occur. An ice cube melting(solid to liquid) will cool its environment. Condensation(gas to liquid) will warm its environment. Ice freezing(liquid to solid) will warm its environment. So believe it or not...fuel endures the phase change from liquid to gas which steals warmth from its surroundings, which is the engine. A lean condition will have more air then fuel...thus not having sufficient evaporative cooling effect it needs. Race engines sometimes have no coolant passages because the race gas burns/cools so efficiently.
Justin Le That is a great explanation. I didn't know. :)
dear Sir matt u ar a great man, wonderful Thank u,
thanks so much really nice presentation very good excellent awesome
Hi Matt my name is Tim i am a 20 year tech and i just thought i would give you a little info about a base line for all MAF cars that are not turbo or super charged. The readings on MAF should be around 1.0 to 1.2 grams per second at idle in park with all accessories off. I know this is only good for those that have scanners but thought you might want to share it anyway.
Hi, Matt! Thanks for your videos! I have a question: I looked on a MAF data On my 4.3 vortec v6, using scanner , noticed that with ignition on but the engine not running, scanner shows me like 2.5 - 2.8 grams of air flow, is it supposed to be like this, or is MAF faulty? Thank you
hi matte, yes indeed I did find this very helpful thank you for your time and videos I really did enjoyed this series a lot and hope will see more like it. one question so cars with[ map] sensor well be different from the one has maf sensor with code p0171 and 174 and with same symptoms that you explained. cheers cheers
That was usefull. Thanks.
This a fantastic vid
Thanks for the reply...Car drives ok, but does lake the power it once had and the gas mileage is poor .It would when new idled really smooth and had lots of power. I have looked at other tests with my launch 123i scan tool. I am going to test out the maf sensor next, because I see the engine timing at idle jumping , and the engine is physically shaking. When you take the foot of the brake and strart to move the engine stopd shaking, I had the engine mounts checked , and had the main one replaced. The scanner is amazing. It will record and play back live data, and you can down load it to your computer and print it. Yep a new Maf sensor is about $260.00 canadian. Next I will check the wiring to the sensor. Some times the cold start is good, ans sometimes not. i will check this out first. If a person has a multimeter you can check out the sensor or better still have a scan tool that has those capabilities.I tried a number of scan tools before I settled on this one. It is not a perfect scanner but well worth the $, if you learn how to use it to its full potential. Done the plugs, cleaned the throttle body, used lucas ... not fixed the problem. Going ahead with the next step... Blessings Ed R
You’re the man. 👍
Well I am XY chromosome profile… calling someone a man doesn’t mean what it used to anymore lol.
32:25 The mass air flow sensor is often hidden to prevent it from getting dirty from oil and particles. It is often in a high location, oil and debris hits and sticks to the protective wall but air travels up to MAF wire.
good one, thanks...
just found your site today, you mentioned self cleaning elements for as MAS, would this be the reason for a burn off relay?
well done
thank you
Great video
Glad you enjoyed it!
Actually, the measured value between the signal 5V wire and 12V would have to change when you engage the throttle. Because the signal wire changes, somewhere between 0 and 5V. So measuring between a fixed 12V and a variable 5V would mean a changing measured value. You would measure something between 7V(signal = 5V) and 12V (signal = 0V).
I'm a software engineer for CNHind NH combines and what we typically do, is use sensors with a valid range between 0,5V and 4,5V. That way we are able to detect short to gnd when we measure < 0,5V and short to Vcc when we measure > 4,5V. That makes sensor diagnostics easier.
Good stuff.
Hi Matt,
Excellent Video keep up the good work.
MarCosMG
+Nigel Marshall Will do!
With the example of the fuel trim and rpm with a dirty maf, wouldnt the ltft stay at 10 (réferenced on a base idle triming needed) and the stft adjusting when more than 10 is needed (ie: raising the rpm)?
What he says at 34:00 was exactly what i have done and pain in the but. I have changed all coils, spark plugs, fuel injectors and even EXHAUST MANIFOLD{which was damaged from top of course } folks, but my rich condition never got solved, And as i keep to investigate more it was my Mass air signal wire which went bad, damaged /twisted and bad reading
Another excellent series. Thanks. I hope you DO do one on MAP only engines, as that is what I have on my Sebring.
Separately, yes, disconnecting the MAF can help identify a bad MAF. A friend had a late 80's or early 90's GM, 3800 I believe, that used a digital MAF. To my recollection (this was a few years ago), the hz did not change much, or it was in too small a range. When I disconnected the MAF, the car idled better AND drove better on the road. Not great, but much better. More drivable. He drove it like that for a couple months until he sold it.
***** It is not that MAF's fail- it's that they get dirty- I have seldom seen a MAF actually fail. And actually I have seen a MAP fail as result of backfire in the intake- it happened on my own car.
But one of the main advantages (at least as far as I'm concerned) with MAF vs MAP only- which I will discuss later, is the ability to modify an engine without re-programming.
Hey Matt, quick question for you. My Mitsubishi has one of those Karmon vortex maf sensors (which aren't the best). So I'm wondering, how do you go about cleaning these? I've considered spraying the honeycombs out with maf cleaner, but wasn't sure about harming it? Obviously there way different than the hot wire setup. It's no wonder many people switch to the LS maf, like yours.
never remove screen. too lean will result.
One word for this video series would be: Excellent! Thanks for sharing your knowledge. As far as cleaning a MAF sensor I have never had any problems using any name brand quality carb cleaner. I'm not sure if the MAF specific cleaner is something special or a marketing ploy for the corporation to make more money?? Take care and thanks for posting
Ozzstar Thanks Ozzy! Yeah same here- I even use throttle body or even brake clean in a pinch all the time and never had a problem.
+Schrodingers Box neither have I. I have heard that some automakers coat the inner walls of the intake or MAF, with a certain material to help smooth airflow and prevent turbulence and using carb cleaner can eat that coating. Whether it's true or not, I'm not sure. But yeah, I've used carb cleaner in a pinch lol
+Brenndon McGill From the look of it at least the aluminum MAF bodies there doesn't seem to be any coating however if there was a coating and it some how was removed by using a corrosive cleaner you could apply some carnuba wax.
Just a note about removing the MAF screen. My tuner removed the MAF screen on my Camaro and it did gain 2 RWHP. But now I'm stuck wondering if my poor throttle response is from removing that screen or something else. It wasn't a good idea. Hopefully your videos will help me figure out for sure if the MAF is reporting inaccurate data.
exactly. removing the MAF screen is one of the biggest myths of performance enhancement there is. the MAF is calibrated to the airflow generated by the screen. removing the screen causes a lean condition and that’s the last thing you want in a power application.
never get advice on performance mods from a chat room!!!!!
I have 2006 WV Pointer. I belive this has a MAP/IAT 4 wire combination. The condition is surging idle. Do you have a video explaining anything similar?
Thank you
man thank you for great work ! your videos are the best... i almost find an answer watching your videos. cold start misire m54b22 engine. have done and tested everything written on internet + ecu + lifters. when i unplug maf it starts x3 time better on cold, almost perfectly. when engine is 45+ degree i plug it back and it runs - 1 + 1 fuel trims. changed mafs 3 times, bought oem but used ones. reading are 98% perfect. 3.0-3.1 grams per second... it is perfect reading for my engine. have any ideas ? compared iat readings with 3 new one with multimeter in room temperatures - they were the same. 2 mafs i used before were leaning mixture to 10% . this one sets on 0. now after 6 months i beleave its overeading a little. could this be a bad timing ? old bmw scan tool inpa does not show any timing problem.
I was wondering the car I have has a rough idle issue. But when I disconnect the MAF it runs almost like new I wonder if there is a wiring issue like my car . Check out this site on how to check for this problem . Not sure if this would help! I am going about the same issue! i have a Launch 123i scanner, that works really well. If you have a scan tool that you can use try it? Hope that helps!
@@Eddythe_Eagle All this time I have been fighting this problem, fixed it with tuning manipulations.
Hello sir, after watching your videos I took a closer look at my dvom and I noticed that it has frequency ranges from 320hz to 32KHz. Do you think it might be able help me diagnose my car should I have an issue? Thanks a ton! 😎
Yes, correct
Yeah I think I got a problem with mine valve body it situated in there maf? it's a Mercedes r170 compressor 03 it looks Sooty I was wondering best way to clean it, can you use brake cleaner or contact cleaner to clean it out is it safe or what do you recommend thanks!
I have heard another bone-headed theory on the MAF sensor screen. Someone once told me that it's only there to keep you from touching the delicate wires. LOL!
Like you can't reach in there from the other side and jam your fingers into them. Gotta love those highly informative forums...
Oh yeah, I almost forgot, replace your MAF!
Hi...excellent 3 part series, i've subscribed!
Hold on though, we still don't really understand HOW the MAF is working do we?
I mean take a 3 wire type sensor...12v supply...a ground...and a 5v signal / sensor wire in the case of a "pull down" type sensor. So the 12 volt supply is heating the hot wire or resistor we assume...or seem to firmly believe it seems...but the 12volt supply is not (in my experience) voltage stabilised, so any readings the computer is getting relating to the current required to hold the temperature of wire or resistor hot...are subject to change depending on alternator charge voltage or electrical load generally in the system, so are we to make the assumption the computer is factoring system voltage into it's calculations?
And if we are correct that the 12 volt supply if for the purpose of heating the wire or resistor, and that the computer is reading the current required to hold a set temperature while factoring in system voltage, my mind is telling me the computer has all the information it needs at that point....so what further purpose or benefit does the 5volt signal or sensor wire provide?
Then my mind started getting into the signal wire and the scope traces you were getting...initially i suspected that the 12volt supply heating the wire or resistor was basic in operation...and that the MAF sensor was "topping" up the current going to the heating section...i say topping up because it was fed 5volts from the computer and it was going somewhere in the MAF sensor...ultimately to ground i suppose????....but is it just getting grounded or is it being used to top up the temperature or is it's purpose just to power a Hz reading?....expanding further the 12volt supply could be doing partial heating and the 5volt could be triggering a relay (mosfet or similar...not an expert!) via a PWModulated action to add extra current to the wire or resistor to keep it hot, and that the result we see on the 5volt wire is the amount of on or off time required to maintain temperature....but then i started thinking if the 5volt is adding any current to maintain temperature that would again indicate the computer would have to know what the base line 12 volt was doing in the first place...which got me back to my original thought that if the computer is measuring volts and current on the 12 volt wire it surely has all the information it needs at that point.
Add to that the scope trace seemed to be showing the on and off time stayed in proportion to each other on the system you were looking at with the engine running...the only difference when increasing revs was that the on / off became much more frequent....the higher Hz you saw...meaning if the proportion stays the same it's can't be adding any current to the heating circuit....so maybe the 5volt wire is measuring the voltage difference across the wire or resistor and that is the reading we get from the 5volt wire???
Do you see where i'm coming from?...we don't know what it is actually doing with the 12 volt and 5 volt wires....perhaps it's not important having said all of the above....but....it's the not knowing precisely that does my head in, and i suspect yours as well.
Here's something else to think about...Scanner Danner says all digital signal MAF's increase Hz as air flow increases and i think you said the same in this series...but i've got access to 2 Mercedes A180 diesels here in Britain....and i can assure you the reading is digital in shape....square wave 5volt on / off signals....and increasing the revs results in lower Hz as the 5volt line becomes longer, while the 0volt line remains constant....and yes the car is able to read this signal and shows increased volume of air entering the engine while the Hz goes down....very puzzling!!!
I suspect we need to send Dave Jones of the EEV blog a MAF sensor...and see if he'll tear 1 down to it's Electronics, with no concern or interest in what the component actually does.
Anyway good videos...many thanks.
+Ian Muggeridge Yep, Matt does fantastic stuff and has a talent for making the complex simle ('ish). Hats off to the man! But there are questions that are raised and I had the same issues as you. Understanding precisely how it works is not just academic. It helps you devise tests. So, I'm not sure: if the analogue (I'll use the Brit spelling) system maintain wire temp using a 12v input, how does it vary current flow to maintain a constant temp if it's not Pulse Width Modulated?
And how/where is the variation in the 5v ref coming from ... How is it detecting variation and delivering a variable voltage output? I'm not an Electronic Eng so I'm also looking to the easy rough schematic that shows the idea of how it is working. If you could test current you might be able to better understand and detect when and why a faulty MAF can sometimes read rich at idle and lean out under load, as the Great ScannerDanner has pointed out.
The resistance of an MAF, a negative temperature gradient thermistor, whose resistance is quite high at low temperature and it decreases with rising temperature.
Hey, Matt. I have been dealing with the dreaded p0101 on a 2015 Nissan Sentra for a long time. Freeze frame data shows a good calculated load value(97%). STFT and LTFT total are below 10% suggesting that the air /fuel mixture is normal and there are no intake or exhaust restrictions (97% load value), and no vacuum leak. The Maf is cleaned, but the code keeps coming back. The biggest issue is that the car has poor acceleration and takes a long time to take off. It has performance issues. Any idea? New spark plugs.
Where is your MAF sensor data. You need to show MAF sensor volume and voltage data.
Hey Matt Thx for the videos. I have 07 Ford Freestar. Showing codes p2295, 2197. Extreme trouble at idol but ran rather well at high RPMs. Between these and the Taurus series, I checked O2 MAF and fuel trims. Sensors showed they ocellated. LTFT both rails 0.0. STFT pegged at 49. You know where I’m going. Exha
Exhaust leak or dirty MAF easiest to check MAF. I cleaned it. It runs actually better than it has in two years. I like your approach. At least I can scientifically mark items off the list BEFORE I touch a wrench. Thx again
How do you explain STFT pegged at 49 but LTFT at 0?
I have been dealing with a cyl one misfire on my 4 banger Mazda B2500 SE. I get diagnostic codes P0231, p0301 and P0402 using a BlueDriver scan tool. While using Live data, I drove a long trip and noticed voltage to upstream O2 sensor would oscillate which is a good sign. However, when engine ran very rough, sluggish, I noticed o2 sensor graph would be flat or a plateau rather than "normal" oscillation. In your expert opinion, does this suggest a bad o2 sensor? I appreciate any help or suggestions. I have already replaced spark plugs, wires, ignition coil packs, fuel filter, fuel injectors, etc.
it suggest accurate reporting of the condition. i would start with what data you have that the plugs, wires, ignition coils, AND fuel filter and injectors were all bad. that seems extremely unlikely. what data showed this was both ignition and fuel related?
grasias por ese video
You recommend a certain manufacturer for map sensors.
could you do a video on evap and pcv understanding/diagnosis?
i really enjoy your videos. very helpful!
keep it up!
Matt I have a problem to solve ,when vehicle is going on a hill road throttle ful open time map is comes to the atmosphere pressure at that time what will be the maf sensor reading because air flow is allready finished
In general the MAF sensor at wide open throttle matches the engine displacement. So a 2L engine will usually read close to 2lbs/min.
18:50 I do have a p0355 and a p0103 right now. Any idea???
OBDII real time reading 89 celsius at 8 am. In the first cold start of the engine.