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Thread: Crank sensor issue? - Do e30s have a "safe mode?"

  1. #1
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    Crank sensor issue? - Do e30s have a "safe mode?"

    I had a weird issue that happened this morning - I'm at the office and haven't had time to diagnose - so i thought Id reach out to anyone that has had a similar issue.

    My 91 BMW suddenly loss power yesterday on the way to work - loss idle, died, started, drove but stumbled at idle for a 1/2 mile or so. I pulled into a parking lot and then it started idling fine. Went to work (a couple of hours) Stared and drove 30 miles home with no issue.

    This morning - started car and let it idle for 10 minutes, idled fine - begin to drive and the car stumbled when leaving driveway. It ran poorly (stumbling idle) -and then experienced a total loss of power. Car would not go above 1500 RPMs - and would not rev - so put foot on gas to keep car moving around the block, but RPMs stayed constant and the car pulled itself around the block at 1500..

    Pulled back into driveway -car was idling - parked in the garage.


    Any thoughts on this condition?

    Does the E30 have a "Safe Mode"?


    I don't have my Bentley here at work - but I wonder if the Crank Position sensor could be bad? Does a bad Crank sensor cause this type of issues?


    NO Codes. Vacuum is pulling at 16 (normal) no problems with hoses, or boots. I recently changed the timing belt (500 miles ago) - so maybe disturbed the wiring on CPS?

  2. #2
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    When I had a CPS go out on my daily, the engine would occasionally cut out above 6k rpm and then eventually did the typical no fuel, no spark, no start.

    Was there any difference in the max RPM in neutral and in gear? It sounds like the CPS or the harmonic balancer might be the issue. Maybe a fuel pressure issue.
    Last edited by hotdish; 02-06-2018 at 12:49 PM.


  3. #3
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    Quote Originally Posted by hotdish View Post
    When I had a CPS go out on my daily, the engine would occasionally cut out above 6k rpm and then eventually did the typical no fuel, no spark, no start.

    Was there any difference in the max RPM in neutral and in gear? It sounds like the CPS or the harmonic balancer might be the issue. Maybe a fuel pressure issue.
    It capped at 1500 or so - Idle is around 750 - 800.

    If I put any load on it, it didn't have any power - but once it was sitting in park - it would idle.. I read somewhere that if the CPS is bad - it will not run - so CPS may not be the issue. I ordered one just in case..

    Would AFM cause this? ECU need resetting?

  4. #4
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    Quote Originally Posted by 95BMWIC View Post
    It capped at 1500 or so - Idle is around 750 - 800.

    If I put any load on it, it didn't have any power - but once it was sitting in park - it would idle.. I read somewhere that if the CPS is bad - it will not run - so CPS may not be the issue. I ordered one just in case..

    Would AFM cause this? ECU need resetting?
    AFAIK resetting the ECU just clears the long term fuel trim, which shouldn't have an effect this drastic. I've had similar issues with total lack of power with a clogged fuel filter or dying fuel pump. See if any local auto parts stores loan out fuel pressure testers and check for gas leaks since it's rust season.

    Both time a Motronic 1.3 CPS has gone out on me it caused random cutting out and restarting at high RPM and then a total no-start in a few weeks or less.


  5. #5
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    Ok - I will change fuel filter - I will also throw in a can of ISO heat (I dont think I have any frozen particles in the line, but it wouldnt hurt) and I will check fuel pressure. I am looking through the Bentley and see the fuel pressure test for a Motronic 1.1 - I assume it is the same procedure for the Motronic 1.3?

    I ordered a CPS (FACET) from Pelican and a Coolant Sensor (BOSCH) also - so I will get both of those changed..
    Last edited by 95BMWIC; 02-07-2018 at 11:22 AM.

  6. #6
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    Quote Originally Posted by 95BMWIC View Post
    I am looking through the Bentley and see the fuel pressure test for a Motronic 1.1 - I assume it is the same procedure for the Motronic 1.3?
    Probably. Motronic 1.3 is the same as 1.1 other than the ECU.


  7. #7
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    Update..

    Before checking fuel pressure (went to HF and bought a cheap gauge) I decided to run the car -make sure it is running like crap - and unplugged the AFM..

    https://youtu.be/f1iaL5YhmTU

    Assuming this may be the issue? Either that or somethings really a miss..

    Will report back after an AFM swap.

  8. #8
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    Quote Originally Posted by 95BMWIC View Post
    Before checking fuel pressure (went to HF and bought a cheap gauge) I decided to run the car -make sure it is running like crap - and unplugged the AFM..

    https://youtu.be/f1iaL5YhmTU

    Assuming this may be the issue? Either that or somethings really a miss..

    Will report back after an AFM swap.
    I'm getting a "This video is unavailable" message.


  9. #9
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    Quote Originally Posted by hotdish View Post
    I'm getting a "This video is unavailable" message.
    Son of a..

    Im not sure what the hell..

    https://youtu.be/f1iaL5YhmTU

  10. #10
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    Quote Originally Posted by 95BMWIC View Post
    Video works. Looks like it's not a fuel supply issue after all and the engine is running lean for another reason.

    You can get a multimeter and check the resistance of the AFM at different openings, but this could also indicate that something else is causing the engine to run lean like vacuum leaks, stuck IAC, bad o2 sensor, etc. The TPS is also worth checking with a multimeter since oil in the intake tends get into it and screw up the electronics.


  11. #11
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    Quote Originally Posted by hotdish View Post
    Video works. Looks like it's not a fuel supply issue after all and the engine is running lean for another reason.

    You can get a multimeter and check the resistance of the AFM at different openings, but this could also indicate that something else is causing the engine to run lean like vacuum leaks, stuck IAC, bad o2 sensor, etc. The TPS is also worth checking with a multimeter since oil in the intake tends get into it and screw up the electronics.

    I got sidetracked - I need to pull an AFM off another one of my E30s to check - but I was assuming I found the issue - Bad AFM. I remember checking one before- its something like moving the flap and measuring resistance? ICV is buzzing and clean. TPS was cleaned a year ago and I still hear a "click" at WOT.. I will check to see if I get a stomp test = if the TPS is bad - no stomp test..

  12. #12
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    Swapped out a good AFM - started and idled fine.. seems like its back to normal after driving 70 miles.

    I think that's the issue.. however -

    I'm not completely convinced - it could be intermittent - I will update again if it begins to run bad..

  13. #13
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    It's back...

    After 300+ miles - driving along on Interstate at 80mph - suddenly began to lose power.. kept vehicle running by putting into Neutral and revving engine to get off and onto an exit. - Idled but would Hunt severely.. nursed it into parking lot... started the vehicle a few times checking different connections.. The car would always start- but would idle real, real rough.. No change when disconnecting AFM this time around.. Shut car off to make a phone call for recovery - started car - idled fine - drove 30 miles (45 minutes) back roads to home. no issues.
    Sitting in garage - just started up - no issues..

    This is what a "scared" looks like to me... (Intermittently dying on the Interstate)

  14. #14
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    sounds like an issue i had, seriously i tried everything. ended up getting a 1.1 motronic and disabling the o2 sensor and cranking idle rpm's up to 950. never had a issue since and the car runs better than ever.

  15. #15
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    Did you swap the harmonic balancer? I don’t know how a metal disc with a magnet in it fouls but I hear it does. I know you messed with the crank position sensor.
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  16. #16
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    Neither of my two e 30’s will run with the afm unplugged, so I’m no expert.

    what happens if the oil pressure switch doesn’t work? Oil level sensor?

    i know you’ve checked the coil but I don’t know what a bad coil acts like.
    1987 325e, coupe, 5speed
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  17. #17
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    When stuff like this keeps popping up sometimes I wish the part would just break completely and leave me stranded just to get it over with.

    Did you ever check the fuel pressure?


  18. #18
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    So here is what I got done over the weekend. I could not get the car to run poorly.. It is running fine. But I had to try something.. so I

    Replaced CPS with a new one (FACET brand).

    Replaced the Main relay with another known working one.

    I also performed the STOMP test - which gave me a code of 1444 (no codes) - which is a bit frustrating..

    Since the Stomp test works - I assume the TPS is working ok..

    The ICV is buzzes and has been cleaned regularly.

    The fuel pump is 1 year old this month and I replaced the fuel filter. - I don't think it is fuel related - when it runs poorly - I can keep it running, and it doesn't turn over a lot to get restarted. I'm not ruling it out completely - but I almost need to have a fuel pressure gauge hard wired in the line to see what is going on. I didn't take a pressure reading this weekend - because it starts and runs fine and has good throttle response.

    Replaced the AFM again (from another E30). The one that I switched to (after the video) was one that I took out of my daughter's E30 - and after a review of my notes - I remembered her car (according to her) was running rough and she through a code of 1215 and I pulled out her AFM and her check engine light went away. This was a while ago (Fall 2017) - and I didn't recall that fact when I put it in mine the other day. SO could I have had 2 bad AFM's? Not quite sure - but cant find a good way to test.

    When the car is running fine - if I disconnect the AFM it will die (as others have stated) - So when unplugging the AFM when it is running badly and it still runs badly - is that an indicator of the AFM.. or of the computer? I have 2 different scenarios above (first AFM unplugged it actually ran a bit better, plugging it in killed the idle and the second AFM unplugged didn't change it running poor)..
    Last edited by 95BMWIC; 02-19-2018 at 11:03 AM.

  19. #19
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    Quote Originally Posted by 95BMWIC View Post
    When the car is running fine - if I disconnect the AFM it will die (as others have stated) - So when unplugging the AFM when it is running badly and it still runs badly - is that an indicator of the AFM.. or of the computer? I have 2 different scenarios above (first AFM unplugged it actually ran a bit better, plugging it in killed the idle and the second AFM unplugged didn't change it running poor)..
    I think the bentley manual or something may have a test procedure for the AFM. Unplugging the AFM makes the engine run in a richer base map, which might cover up something else causing the engine to run lean.

    I was going to suggest that you may have had a bad AFM connection, but having it die completely with it unplugged and having no difference when it is running badly makes me think that there is another issue somewhere.

    Does the car run with the o2 sensor unplugged?


  20. #20
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    Quote Originally Posted by hotdish View Post
    I think the bentley manual or something may have a test procedure for the AFM. Unplugging the AFM makes the engine run in a richer base map, which might cover up something else causing the engine to run lean.

    I was going to suggest that you may have had a bad AFM connection, but having it die completely with it unplugged and having no difference when it is running badly makes me think that there is another issue somewhere.

    Does the car run with the o2 sensor unplugged?
    Bentley states - "no electrical test specifications are available for the air flow sensor installed on the 6 cylinder models". It states to check sensors input signals from the CPU.. Looks like test for resistance on PINS 7 and 12 on the Motronic 1.1 325i but no info for the 1.3. But the issue would be that testing it while it is working most likely wont explain anything - its not throwing any codes now.

    The car does RUN without the O2 sensor - no change. https://youtu.be/xSdBxZH9PhU

    Car dies if AFM sensor is unplugged - However it will run fine with the AFM unplugged once re-started. Maybe thats the difference - I must restart it for it to run wit AFM unplugged..

  21. #21
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    I’m enjoying reading this stuff so thanks for the info and painstaking posts.

    early on I was under the impression that if my car wouldn’t run with the afm unplugged then something was wrong.

    now, both my e30 cars run very nicely and neither of them will run without the afm, so, whatever.

    good luck and I sincerely hope you get things sorted. I wish I could help
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  22. #22
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    Quote Originally Posted by 325e '87 View Post
    I’m enjoying reading this stuff so thanks for the info and painstaking posts.

    early on I was under the impression that if my car wouldn’t run with the afm unplugged then something was wrong.

    now, both my e30 cars run very nicely and neither of them will run without the afm, so, whatever.

    good luck and I sincerely hope you get things sorted. I wish I could help
    Try unplugging the AFM, AND then re-start it.. I believe it will run after re-starting it..

  23. #23
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    Just updating this thread in case someone else has similar issues..

    The AFM I replaced in post #12 was used and thought to be in good working order - it was not (See post #18). I swapped out to yet another AFM and have not had any issues whatsoever since then..

    In summary - AFM can definitely cause idle issues and intermittent stalling...

  24. #24
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    AFM can have varnish build up inside the unit resulting in a sticky flap door. Similar to the ICV not working properly. Take off the AFM and check to see if the flap door is sticking when you move it with your hand. If it does, spray carb cleaner down it to remove the varnish build up and then test for movement. Reinstall and run the car.

  25. #25
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    Quote Originally Posted by Ceekers View Post
    AFM can have varnish build up inside the unit resulting in a sticky flap door. Similar to the ICV not working properly. Take off the AFM and check to see if the flap door is sticking when you move it with your hand. If it does, spray carb cleaner down it to remove the varnish build up and then test for movement. Reinstall and run the car.
    Good advice..

    Of Course, mine wasn't that easy - it was the Potentiometer Conducting Strip that was worn away... Need to send it out to service..

    Cool little link on the BOSCH AFM.. http://clarks-garage.com/shop-manual/elect-22.htm (Info directed on the Porsche' however the internals are very similar)

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