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Thread: misfire around 3500 rpm when engine is warm

  1. #1
    Join Date
    Aug 2019
    Location
    NJ, USA
    Posts
    60
    My Cars
    1994 E36 325i

    misfire around 3500 rpm when engine is warm

    I finally got a chance to record the problem with my 325i.

    https://www.youtube.com/watch?v=1ppopEAZTgo

    You can see the temp guage is in the middle and when rpms hit about 3500 to 4000 it gets really rough and the CEL blinks. When the engine is cold, it runs totally fine. I have changed the spark plugs, and today I tested the coils with a spark tester, they were all good.

    Also worth mentioning, last week I had a check engine light. (OBD1, can't scan) Did the stomp test. got code 1215, MAF Sensor. I cleaned it with MAF cleaner, let it dry and reinstalled it, same problem. Took it to a local mechanic. He said no vacuum leaks and he thinks it's the catalytic converter. He said the MAF code was old so he cleared it. On the chance he was lying, I decided to test the coils myself but they were fine.

    Today I did the stomp test and it gave me the MAF code again.

    This was the car first thing in the morning when it was still cold. Runs totally fine for the first 15 minutes or so.

    https://www.youtube.com/watch?v=eFmZ7HYthk8

    Is there a way I can test if the cat or maf is the problem?
    Last edited by NuruiGumi; 12-07-2019 at 09:56 PM.

  2. #2
    Join Date
    Nov 2013
    Location
    oneida, ny, usa
    Posts
    4,680
    My Cars
    325ic,328is,03 325i
    Thats a much better worded post.
    It sounds as if it has to do with the system getting to OT. Id bet its a lean condition caused by an error. Probably a coolant temp sensor, ait, maf, tps, or 02 sensor with a faulty reading causing the misfire when the ecu goes into open loop.

    - - - Updated - - -

    Also. You have to check the coils while at running temp. (I would also check the crank and cam sensor). Heat is a large part of coil or magnetic sensor failure or reading. And entirely possible that they only go out of phase when at OT.

  3. #3
    Join Date
    Aug 2019
    Location
    NJ, USA
    Posts
    60
    My Cars
    1994 E36 325i
    Quote Originally Posted by spyderg0d View Post
    Thats a much better worded post.
    It sounds as if it has to do with the system getting to OT. Id bet its a lean condition caused by an error. Probably a coolant temp sensor, ait, maf, tps, or 02 sensor with a faulty reading causing the misfire when the ecu goes into open loop.

    - - - Updated - - -

    Also. You have to check the coils while at running temp. (I would also check the crank and cam sensor). Heat is a large part of coil or magnetic sensor failure or reading. And entirely possible that they only go out of phase when at OT.

    i tried to disconnect the maf. the car cant run at all without that connected. it just dies right away. you can rev it but the second your let off, it dies. i drove around to warm up the engine until i started sputtering, then retested the coils. couldnt find one that was weaker than the others. the spark looks bright and consistent. if you pull one of the coils, the engine suddenly gets a lot rougher. i thought maybe if i had a weak one, it wouldn't change much when you pull it but that wasn't the case. then i wanted to pull the pre cat o2 sensor. i thought if the cat is clogged, then this would allow the exhaust to vent and i should see a difference. but i couldnt remove the o2 sensor. i soaked it in pb blaster and i tried with a long 22mm wrench for a long time, i even tried hitting the wrench with a hammer, i tried kicking it with my heel, but it would not budge at all. So i pulled the connector off that sensor just for the heck of it to see how it would drive. i didnt notice any difference. weirdly didnt even get an o2 sensor error code. im gonna see if i can find a better way to remove it.

    the one thing i found though that i hadnt noticed previously is that it wont let me rev past 5000 rpm. the needle bounces off the 5 and the CEL flashes, so ... it is looking like it could be the cat but who knows.

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