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Thread: Crank Position Sensor - to replace or not replace...

  1. #1
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    Crank Position Sensor - to replace or not replace...

    ...that is the question. In my never-ending quest to solve my relatively minor erratic idle problem, I pulled my crank position sensor today, as it was extremely dirty. While I was cleaning it up I noticed that a bit of the plastic toward the sensor end was brittle and some of it had come off, allowing the sensor to twist a bit within the wiring. It could very well be the original sensor. I bolted it back in, and there was no discernible change in my idle. I've read a lot of conflicting information on the crank sensor. Mainly: 1) it either works or it doesn't (and when it doesn't the car does not run, since the fuel pump won't operate); or 2) it can affect idle and cause other running issues.

    Since my car is otherwise running well, aside from a less than perfect idle, does it seem worth spending the $ for a new sensor? Resistance for the sensor is right on spec at 540 ohms, but it seems only an oscillator (which I do not have) can truly check its proper functioning. If #1 is true, it would seem to not be worth replacing it. I've basically run all through the possible causes of my erratic idle at this point, save for checking compression (and if it's a compression issue, there isn't much I'm going to do about it right now!), so it would be a shame if I ruled this sensor out when it could still be causing my idle issue. Thanks for any thoughts!
    Last edited by schnell944; 12-12-2018 at 10:26 PM.

  2. #2
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    regarding your idle issue, have you checked every vacuum hose? icv, tps, and maf? these things have their own job for car performance..

  3. #3
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    also check all ignition wires, from end to end incl. the boots 6 Kohm. Maybe one cylinder is not getting sparks? But that you would also see from the spark plugs, if you compare them, color might be different, spark plugs can tell us a lot
    https://www.championautoparts.com/Pa...ark-plugs.html
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  4. #4
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    Thanks, G46 and shogun. I've checked all of the above at this point, read all the good checklists on here (and your site, shogun) and pretty diligently pursued every avenue. Checked every hose/gasket; cleaned the icv (improved the idle from when I initially purchased the car 7 months ago), checked tps, cleaned the AFM, replaced wires (one was corroded and not to spec resistance), replaced plugs (original ones all looked good, just old), adjusted valves, replaced o2 sensor, replaced fuel pressure regulator, replaced temp sensor, etc., etc. Only other things I can think to do is take it to a shop for a smoke test (though I don't want to pay the $300 the local shop would charge) or to swap my AFM for a known good one from someone in the Northern VA area.

    Idle feels like it's randomly and lightly missing here and there, and I can feel it from within the car. Runs smooth above idle. I'm sure I'll figure it out eventually! Just wondering if there was any possibility the crank position sensor could have anything to do with it.

  5. #5
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    if it ran good above idle, it must be some sort of idle circuit. how did u check your tps?

    https://www.bimmerforums.com/forum/s...&highlight=TPS

    thats the link on TPS check

    pin 4&6 should have continuity when idle. no continuity off idle. im thinking that your car is having TPS problem, where it does not activate the idle circuit. its adjusting its Air fuel ratio according to the MAF, but ICV did not open to let enough air in (throttle body butterfly flap closed) you try and smell the exhaust fume, is it more into smell of fuel or burn smell..

  6. #6
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    I checked the TPS a while back according the the Bentley manual 130-16. Will read through the thread you reference. Exhaust smells fuel rich.

    *edit* just re-checked my work on the TPS and confirmed that it's functioning properly. Continuity on idle, no continuity off idle at 4 and 6. Continuity at pins 4 and 5 at wide open throttle.

  7. #7
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    whats your idle atm? how about rising the idle just a tiny bit. see if its getting any better. by adjusting the cables on the throttle flap, i cant remember if there is
    1990 730i M30B30 RHD - Sold
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  8. #8
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    It idles at about 800rpm. I'm not sure adjusting the idle via the cable is the best approach, as it would just be masking the problem. Bentley says the cable should have some slack in it and leave the idle speed adjustment to the ICV.

  9. #9
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    Quote Originally Posted by schnell944 View Post
    Since my car is otherwise running well, aside from a less than perfect idle
    Hey Schnell, I have the exact same issue with my '88 735i. I've replaced every vacuum hose, the O2 sensor, the fuel pump & the filter multiple times, the fuel pressure regulator, the plugs (correctly gaped)/wires/distributor cap & rotor, checked every electrical control unit & grounds, and cleaned as well as swapped known-working MAF's, TPSs, CPSs, and ICVs. The idle is still kind of erratic and seems like it misfires here and there. Also, sometimes the idle surges when its cold and I just started it. Lastly, if I let off the throttle while driving at around 1500 rpms, it will surge for a second before settling down. Otherwise the engine runs great.

    So I feel like we've narrowed our issues down to two possibilities:
    1) there is a vacuum leak at the intake manifold, valve cover or elsewhere that can only be found with a smoke test.
    2) the injectors need to be cleaned/refurbished/replaced.
    \\edit\\ 3) the engine needs a valve adustment?????

    I'd love some input from others though!!
    Last edited by CamE32; 12-15-2018 at 07:04 PM.
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  10. #10
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    Glad to know we're in this together, at least! In my case I've also taken care of #2 and 3 -- had my injectors rebuilt and adjusted the valves recently.

  11. #11
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    Hmm, interesting! I have a new valve cover gasket I think I'll put on next to see if that helps.
    1983 4-spd Mercedes 240d w/403k - Sold!

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  12. #12
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    btw, your engine is m30? theres one hose bigger from others from under the intake manifold going to ICV , its pain in the A$$ to get it off, best way is remove the intake manifold..if that hose is not good, it affects the idle also..

    here, clear picture of the "hose from ICV" port

    https://www.bimmerforums.com/forum/s...ght=M30+intake
    Last edited by G46; 12-17-2018 at 12:08 AM. Reason: added more info
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  13. #13
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    Yes, the is very important, that controls the idle control valve http://i1275.photobucket.com/albums/...ps332ecaea.jpg
    And even if it looks o.k., I would change those hoses all. I wasted $$$ on my E36 M3. When I started the engine cold, there was always the noise like the infamous Vanos chattering, disappeared after abt. 1 minute. Also checked other places, asked people. All were of the opinion: Vanos problem, we even checked with a stethoscope. A member here from the E32 forum went to a scrapyard in the US and bought me a used E36 secondary airpump (new ones cost >> $400.00 ) , http://www.realoem.com/bmw/enUS/show...diagId=11_1540
    Installed it, nothing changed, bought a Vanos repair kit and special Vanos tools from the US, incl. shipping almost $200, alarmed the wrenching buddies that a bigger operation on the M3 engine is necessary.
    Spent some hundreds of $ for nothing, then one day I checked again the hose which goes from the secondary air pump to the #14 valve, which controls the valve. http://www.realoem.com/bmw/enUS/show...diagId=11_6092 found nothing wrong, but thought, well, give it a try, replaced # 12 Vacuum hose black 3,5X1,8 11727545323 by a silcone hose, problem solved! The vacuum hose with the holes did not have enough vacuum to hold the spring loaded valve and that was flipping always and made that noise.
    Then I inspected that old vacuum hose, when bending it, I could find a lot of cracks. I wasted some hundreds of $ to solve this problem, actually the problem was only a cheap vacuum hose.
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  14. #14
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    I should probably replace all the vacuum hoses on my M30 too. Is it difficult to remove the intake manifold for someone who's never done it? Do you need to replace gaskets when reinstalling?

  15. #15
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    Yes, it's the M30. Good point on the ICV hose! It's one of the few hoses I have not yet replaced for the reasons mentioned by G46 above. I'm not sure I really want to remove the entire intake manifold if I don't have to. Anyone have success replacing it with the manifold on? It very well could be the culprit here (though I thought that about the last 20 things I've checked I've visually inspected it and sprayed it with carb cleaner, but I should probably replace the whole thing.

  16. #16
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    Quote Originally Posted by Cactuar View Post
    I should probably replace all the vacuum hoses on my M30 too. Is it difficult to remove the intake manifold for someone who's never done it? Do you need to replace gaskets when reinstalling?
    yes sir, need to replace the gasket, or you will end up with erratic idling and misfiring from the leaks on the intake gasket. its post MAF leak, so yea those air are not calculated and fuel is not added, causing lean and misfiring.

    Quote Originally Posted by schnell944 View Post
    Yes, it's the M30. Good point on the ICV hose! It's one of the few hoses I have not yet replaced for the reasons mentioned by G46 above. I'm not sure I really want to remove the entire intake manifold if I don't have to. Anyone have success replacing it with the manifold on? It very well could be the culprit here (though I thought that about the last 20 things I've checked I've visually inspected it and sprayed it with carb cleaner, but I should probably replace the whole thing.
    if you happen to have a friend with tiny hands, might have a chance of success, or else, its very hard to fiddle around the bottom of the intake.
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  17. #17
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    Looking at it now, i think I'll be able to replace while keeping the manifold on. Ordered the hose and will report back.

  18. #18
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    Quote Originally Posted by schnell944 View Post
    Looking at it now, i think I'll be able to replace while keeping the manifold on. Ordered the hose and will report back.
    If you're going to get in there, in back of the intake manifold to replace the hose coming from the idle control valve, while you're there you might want to replace the only other hose that goes to the back of the manifold and that's the purge valve hose. When we had my manifold off and we replaced both vacuum hoses these other two were really in bad shape. If the manifold is off it's a breeze, if not you need somebody with small hands. If you follow the hose coming off of the charcoal canister to the purge valve clipped to the intake manifold you'll find it easy. It just pushes on to the other side of the purge valve and hooks onto the back of the manifold. The hoses look like this. Can really mess up your idle if thy're not in good shape.





    Last edited by CroughtonE32; 12-18-2018 at 04:49 PM.
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  19. #19
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    You read my mind! I purchased those two hoses last night. The purge valve to manifold hose seemed a bit dodgy/hard. Will check back in once I get both in.

  20. #20
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    well, its good that you checked every other thing as part of "preventive maintenance" even though this hose to ICV might be the main culprit. hopefully it will fix your erratic idling, when you mentined above idle is fine, i believe it will be within the idle circuit
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  21. #21
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    Agreed. Fingers crossed. Appreciate your and everyone’s insight!

  22. #22
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    do you work it on your own? or get somebody to do it? also one thing needs to be checked, if your brake happen to be stiff or something, theres a also a hose with a check valve, those check valve and hose need to be inspected also.
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  23. #23
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    I work on the car myself. Thanks for pointing out the brake booster hoses/check valve. I replaced the two hoses going from the manifold to the booster. The check valve seems ok. I also replaced the rubber gasket at the booster where the hose fitting plugs in - it had a vacuum leak so big I could hear it! Appear to be good on that front now.

  24. #24
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    no news yet for the ICV hose?
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  25. #25
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    Not yet. Still waiting for the two hoses to arrive. They’ll probably get here after Christmas at this point. Will be sure to update when I get them on!

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