Diagnosing random misfire without check engine light or codes
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- Опубліковано 4 жов 2024
- 2001 Chevy S10 with hesitation and stumbling, occasional misfire but owner brought in after clearing check engine light and erasing codes and freeze-frame.
Can a logical, systematic approach prevail and still find the problem?
Excellent step-by-step tutorial...thanks!
Awesome video, learned a lot in a few minutes. I've been dealing with a random misfire with no codes for a while and now I have a different approach thanks to this video. Greatly appreciate it.
thank you so much. this video made it very clear how to rule out possible problems before I start dumping money in my car. Thanks!
Thanks Matt great video thanks for sharing your experience and your knowledge thanks some much
Thanks for the comment, yes I am a DIY however I do make money on the weekends doing this stuff. I typically go flat rate and seldom charge more than 100 bucks even for serious repairs.
Rod knock test video was very informative, thank you
very good video.
thank you very much for teaching us how to diagnose
@ Integrab- sorry for the late response, I'm sure you figured out your issue by now and if so please share your finding to help others. But the approach I'd probably take- and I hope this doesn't sound remedial but I want to be sure you also tried your timing light on other plug wires just to confirm the timing light works... just saying. If it does work, I'd then put a spark tester between the cap tower at #4 on the new cap you have and a direct ground and look for spark that way.
Very Well Made!! Keep up the good work.
Agreed. I have no explanation for that- even though the misfires were intermittent, it sure seems it would have lit the MIL. What can I say- it never came on, even during all this testing. My scan tool is capable of reading "possible codes" (e.g. codes that have occured on one drive cycle but not on consecutive drive cycles) and I didn't think to look at that, maybe it would have shown a possible code. But even then, misfires that frequent don't usually need consecutive cycles to light MIL.
Another Great Video, Matt,
Hi Integrab, sorry again for late response, I'm traveling for my "real job" a lot and slow with responses. Sorry to hear you're having issues. OK just to clarify one last time- you are missing spark ONLY at #4 as confirmed by a spark tester installed AT THE #4 TERMINAL ON THE DIST CAP CONNECTED DIRECTLY TO GROUND, correct? And further this is also AFTER replacement of the cap, correct? If so then not only will I try to help but I think this would make a great video for you to produce!!
matt
Thanks, Alex. I love them too. The scan software used in the video is AutoTap from B&B Electronics however it was discontinued some years ago. Just this year I upgraded to AutoEnginuity which offers much more capability and even some bi-directional capabilities. While I thought AutoTap has a better user interface, there is no doubt AutoEnginuity is a more powerful system.
Very informative, thanks for posting it!
Man, you are good! I am glad I found your channel. Are you DIY and not a professional mechanic, right?
thanks for all the above i learned a lot in a short time , i asked myself if this would be possible of opening the electricity connections from O2 bank 1 sensor 1 and connect the power cords from bank 2 wire bank 1 destined to the PCM , any wires that the PCM works with one sensor which is O2 bank 2 sender 1 .
More great stuff. You're a rigorous thinker. All information must "jive".
Regarding exhaust leaks, my expectation is that exhaust back pressure just blows out rather than sucks in air to cause a lean low voltage O2 sensor. Or is there an aspiration effect that overcomes this back pressure? It's probably a bit complicated by pulsed exhaust flow at low engine power too.
Thanks again.
Go to his discussion page after clicking on his channel. There is a big post covering O2's actually detecting hydrocarbons, not O2. Gojudude started the thread.
The reason it was taught that it detects O2 is that it'd make it easier for mechanics to understand.
Occasionally knowing that it's seeing hydrocarbons makes situations clearer. Before reading the statement I was already suspecting it was true since it didn't logically fit with all situations.
I believe in an exhaust leak above an o2, 2 things will happen. Some hydrocarbons will escape causing the engine to look like it's running leaner than it is. At higher flow, the venturi effect of the exhaust going over the leak will pull outside air in. The system can show it's "leaner" just because it's cooler.
When I had an exhaust leak in front of my catalytic converter and I had a high load or high RPM it'd make air burp into the system.
My post catalytic converter would show rich at these times. Why? The exhaust was being cooled and the cat wasn't hot enough to burn the hydrocarbons. Usually when driving slower, the rear o2 would show leaner, showing a good burning of the hydrocarbons. Realize, that when a cat isn't working the lean/rich will happen much more rapidly showing that it's bad. Whether it's more rich or lean doesn't matter as much as if it's mostly steady. At that point the ECU will think it's healthy cat.
All this comes together for me, because the exhaust leak would frequently spike rich on the rear o2, and that switching told the computer I had a bad cat, even though it was new. The ECU was fooled, but I'm no longer fooled by the difference. I can tell when watching live scan data.
WD? Thank you for the comment, it got me really thinking. :)
@@DENicholsAutoBravado your comment just solved my issue and helped me understand how 02s respond to a bad cat
@@issamenu5en5e29 Happy to have helped! I really love geeking out about oxygen sensors. I have years of experience since this comment and plenty of playlists if you feel like seeing more examples. It's one of my favorite subjects to cover/my cars and trucks have given me the opportunity to show a lot of examples. I generally don't show the fixes at work, just the ones at my home garage so if it doesn't break on my car, I don't hit record. LOL
wow another great video
My car runs weird too after warm up. When idling, you can hear the exhaust make a intermittent popping noise and my left tailpipe doesn't have much noise coming out of it but you can hear the noise from both sides. Also when I'm driving when coming to a stop the idle comes down kind of slow then stays at about 900 rpm for a second then burps back down to normal. BTW my car is a 2003 mustang gt. Any ideas?
YzfR6 hey! Did you ever fix the problem? I have the same issue rn.
I wish you were in Metrowest Boston area! One of your video said something about Colorado Air Quality Board, so I suspect, it would be a long drive for me to bring my vehicle to you :-)
Thank you so much .. nice help ...
I would have thought the computer would immediately flip a code, and it's disconcerting that the code didn't quickly reappear.
thank Mateo great video, can I test the down stream o2 sensor the same way, to find out if it's the o2 or the catalyst converter on po420 code ,or how do I know which is the problem, cheers from ontario ca,
I had a P0001 code on the scan tool. And the evap was blinking. This car has never had its fuel filter changed in 15 years which I have owned it, I am just guessing there may be a flow restriction. I have a fuel filter I purchased a number of years ago which I have in storage which I will finally change to see if it helps. I suppose I need to check the fuel pressure and fuel volume. Never had any issue with the car in this regard. I am not sure what test would tell me if something is wrong with the evap system. I do know there is suppose to be a valve which should open after the fuel canister. From what I have watched on youtube it is suppose to open when the car first starts to remove any fumes with in the canister.
i wish my hummer was this easy. all my fuel trims are excellent..02 sensors perfect..replaced all ignition system twice..new seals and gaskets all the way thru, compression is perfect on all cylinders, even replaced battery twice. still get random misfire on all cylinders with no codes. its been a year and I still have no clue what is causing it
well I would totally start with the ignition system. you say you replaced it twice - what was the data you were seeing that kept indicating the ignition was failing? That’s totally the clue!!
You still could have burned out the cat converter from that rich condition right?
Hey ive watched a couple of your videos, nice job. Quick problem that you might be able to solve ive got a cyl 4 missfire that ive located to cyl 4 with a inductive style timing light around 1800 rpm spark just dissapears from cyl 4 what could cause this on that one cyl ive swapped plugs wires coil cap rotor etc something is effecting cyl 4 could it be crank or cam sensor? Im at a loss
12:00 I totally agree with your comment. It was obviously running rich. I haven't watched the end of the video yet. But I believe the ECU was trying very hard to richen up a lean condition that didn't exist.
I hope this customer came back with any new check engine light. I suspect a catalytic converter getting destroyed....depends on how long this was going on.
Actually no I haven't solved the spark issue in cyl4 still yes I did confirm that the spark is working in other cylinders at the time it looses spark to that cyl you can see the event happening as you accelerate the engine, and if I put the timing light on the coil wire you can see the something happen weird with the spark on that cyl4
Why doesn't this dang video play? After you hold up the sign that says this is our story it keeps jumping to the next video on the list. No way around it. I tried many times to skip further into the video and it wouldn't.
I have a 2006 chevy silverado 4.8L that has a P0300 random misfires trouble code. This is the only code I have active. The misfire seems to be constant. Do you have any tips I could use to help me diagnosis my issue. I have some data that I captured that maybe you cold help me pin point my issue. STFT B1 = 0.8%, LTFT B1 = -7.0%, STFT B2 = 1.6%, LTFT B2 = -0.8% Intake manifold absolute pressure = 33kPa, engine rpm =539, engine coolant temp= 92°C, Intake air temperature = 27°C, mass air flow sensor = 4.8 g/s, 02 sensor output voltage (b1-s1) = 0.14v, STFT (b1-s1) = 0.0%, 02 sensor output voltage (b1-s2) = 0.845v, STFT (b1-s2) = 1.6%, 02 sensor output voltage (b1-s1) =0.11v, 02 sensor output voltage (b1-s2) .73v, STFT (b2-s2) = 99.2%. Hopefully this helps. I've watched a few of your videos and have learned a few things. keep up the good work and looking forward new videos.
I don't understand why are you using those data oaramaters? What is your focus- what is the reason for ST^FT and LTFT without a load curve? Why do you have IAT on there? Do you suspect an IAT issue and why?
It looks to me like you just randomly dumped the entire data set. You need to collect data that is relevant to your hypothesis. There is nothing useful here, sorry.
my scanner is showing the mil light is off but is showing po300 and po455, there is no check engine light but still showing these codes and it's puzzling me.
What your scanner is probably showing is called a "pending code". For the MIL to light up, you need to meet certain criteria- usually it's the condition for the code must be might in two consecutive drive cycles. If it is met in only one cycle the computer registers a "pending code" but waits for the rest of criteria to be met for lighting the MIL which is called a "confirmed code". If the fault happens only every once in a while you may perpetually keep a pending code but no confirmed code.
The pending code usually disappears on it's own if other criteria are met- usually around 20 drive cycles with no detection of the code.
Keep in mind it is also possible your MIL light itself is not functioning. If it comes on during a Key-On Engine -Off (KOEO) test then indeed you just have a pending code. If the MIL light does not come on during KEOE you have a bulb out or missing or other actual MIL indicator malfunction.
Lol the beginning!
Id like to have seen how you hooked everything up to the oxygen sensors or did you get that strait out of the OBD2 port?
I just used a basic scantool is all
+Schrodingers Box I'm wanting a good scan tool and scope. A used snapon Modis with an integrated 4 channel Scope looks appealing.
I like the idea of a PC based scan tool and scope because if the lap top breaks I can fix it or replace it and simply reload the software as opposed to sending the Snap on in and getting the ole - you might as well buy another used unit for the cost to repair this guy routine.
FYI, I found this article www.nonlintec.com/sprite/cap_failure/, describes the poor quality of condensers leading to arcing, they recommend a better capacitor -condenser, but I re-read it, gave it some thought, then I put a 2nd condenser on the coil -ve post, reason - the chance both condensers arcing at the same moment would be remote, and thus the non-arc condenser electrically kills the arc of the other, my long time problem in L20b Nissan engine is cured, so - on any engine with points and condenser, replace 1 old condenser with 2 new for great results
Can you tell me where can i buy that autotap cable for laptop, software seems to be free to download?
Autotap is no longer supported sorry
how do u use your laptop to do all that? please and thank u
+Ivan Hernandez You can use an OBD2 software for laptops, and as long as your laptop has Bluetooth capability (and the OBD2 scan tool does as well) you can synch them together and troubleshoot. Same as for iPhone/Android.
i have a 2003 Chevy s 10 pick up random misfire at idel at times rough idel at times not all the time once a week or so started off as cylinder 4 misfire replaced cap roter wires coil pack fuel pump spider injector got rid of cylinder 4 misfire
now get the random misfire replaced cap roter disturber crank shaft sense o2 senser Catalytic Converter mass airflow
had large e vap leak replaced Vapor Canister Purge Valve Vapor Canister Vent Solenoid replaced lines to fix it by replacing the filler neck smoked engine no signs of leaks
fuel psi 55
no other codes but random misfire
take it for a sticker but your vehicle was rejected because it was "Not Ready.
Catalyst Efficiency Monitor Not Ready EVAP Monitor Not Ready drove it for 7 - 8 days still not ready
When GM cars have a random misfire detected, they go into "OL3" mode which will basically prevent completion of the emissions monitor testing. You have no choice but to fix the random misfire.
jon white wow that is a lot pf parts thrown at it. Should have just bought a new car...
Damn with the cost of all those parts you could have got a professional diagnostic, repair and probably keep some change in your pocket. ;-)
so he did not have any codes in the computer? I am beating my head on a rock with my pickup right now. I have no code in the computer at all. So much so that I checked to make sure the damn light was on the dash wouldn't burn out. I'm having the sameproblem I have no codes thrown to the computer I'm using a lot of fuel have a stumble during driving range but not at idle. I just had both heads replace because they both cracked on a 96 Chevy c 2500 5.7 liter vortec VIN code r.the reason I'm thinking this is what is happening with mine is because I flushed a hell of a lot of coolant out the exhaust pipe before I found out where my leak was.prior to having the head replace the truck ran fine it just burned as much coolant as it did gasoline. LOL
What data do you have?
@@SchrodingersBox thank you first of allit's a 1996 Chevrolet Cheyenne extended cab 5.7 l VIN code r two wheel drive manual long wheel base. I had to have both hips replaced because they cracked it was just a flaw in the first-year vortec motors.prior to this the truck ran like a top even with it leaking coolant into the exhaust it ran great. Now I have new heads on it and everything but I'm having a bad hesitationalmost what I would call a Miss at driving range it doesn't do it while the engine is cool but once it gets up to operating temperature it has a hesitation at driving range but not at idle. It has not thrown one single code so much so that I checked to make sure the light in the dash was still working.I'm leaning toward the oxygen sensors being bad because so much coolant went down the exhaust pipe
@@SchrodingersBox it didn't throw a code at all I have no code whatsoever except it's using a lot of gas and has the hesitation during driving range but not at idle. The fuel pump I've checked and it's operating better than it should. They put a new fuel regulator in it because they were already there only stupid spiders. I talked to the mechanic himself he said everything on the spiders look good and they went right back in splendidlyand I'm not I even sprayed it with carburetor cleaner all the way around while the engine was running and it didn't pick up.what is got me for a loop is as bad as this thing is missing and as much fuel as it's using I don't have a code at all
I need basic fundamental starting data. That’s not data. What’s the rail pressure at static vs load? What’s the shirt and long term fuel trim when curved against load? What’s the MAP and MAF output?
I need something to work with as a basic starting point.
@@SchrodingersBox oh I understand and I apologize for assuming or not telling you beforehand. I don't have a way to harvest that information from my vehicle. Watching yours just now I would be very surprised if it's not my O2 sensors.I'm going down to the local U-Pull-It wrecking Yard tomorrow to get some other stuff for my truck cuz I converted it from a bench seat to captains chairs and I'm going to find one that is wrecked so I knowat least that motor was working choir to hit him whatever it hit and harvest before O2 sensors and see if it makes a difference and then if it does I'll just order brand new ones. Hey I appreciate you posting this video you're a lifesaver because that's exactly what mine is doing
so why didn’t the oxygen sensor throw a code?
If I recall, the codes where reset when the vehicle was brought to me weren';t they? Probably did have an O2 stuck lean code before.
Put some leg's on it .... It would run better .
Get to the point and say what it is 😂 everyone says could be this and that but it's a sensor probably but a vacuum leak or spark plugs smh
*Butthead voice* Uhhh huhuhuhuh leaning towards