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Thread: 2005 120i engine shudder

  1. #1
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    Question 2005 120i engine shudder

    Hi all, hoping for some advice and pointers so I can start troubleshooting/fixing this.

    Short story: engine shuddering, seems to fuel cut under load at around 3000 rpm

    Long story/background: Picked up a 2005 120i recently; definitely my favorite chassis after the E46. We've been on a road trip, driving a few hundred kms a day and haven't had any issues. Then, after parking overnight, the car suddenly developed a shudder and some misfires. Ran the codes and drove it to our next destination (Cairns, so should be able to get parts, at least delivered). Seems like a fuel cut around 3000 rpm under load, and power output is low. Engine shudders and varies RPM constantly by a small amount when driving, but it's driveable, just have to take it slow. Feels a lot like clogged injectors, but that's probably not the problem, looking at the codes and running through some injector cleaner (which made no difference), and given the fuel cut around 3000 rpm. After warming up, engine needs some gas to restart, but otherwise seems to shudder about as much as cold.

    Warning lights:
    DSC (yellow)
    brake symbol (yellow)
    engine (yellow)
    tire pressure (yellow)

    Codes:
    Code:
    002B5C -- DME: Crankshaft sensor
    002B5D -- DME: Crankshaft sensor
    005E1A -- DSC: Engine management: interface
    002C6D -- DME: Oxygen sensor after catalytic converter, ageing (makes sense due to misfires)
    00A6D1 -- JBE: Auxilliary-water pump (existing fault; probably unrelated)
    009CBC -- FRM: Short-circuit fault 1 (existing fault; probably unrelated)
    009CC2 -- FRM: Communication with mirror, passenger's side, disturbed (existing fault; probably unrelated)
    00930B -- FRM: Dipped beam, right faulty (existing fault; probably unrelated)
    00FFF2 -- MOSTSYS: MOST ring break
    S 0195 -- No communication possible with: Telephone control unit (existing fault; probably unrelated)
    I have some theories, but before I throw parts at it and/or possibly go down the rabbit hole, I'd like to hear from you all. Thanks!

    (P.S.: would rather work on it and/or fix it myself, but would also take recommendations for a good indie shop in Cairns, QLD.)
    1991 MR2 NA | 1988 M5 | 2000 740i Sport | 2004 M3 |
    2009 SMART | 2006 S2000 | 2005 120i | 2006 S500

  2. #2
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    Leaning strongly toward this being electrical, since a) the only thing that happened/changed was the rain shower, and b) there's a wide variety of errors some of which are known to be incorrect (e.g., tire pressure). Apparently, water getting into the trunk and causing this problem is typical for the E87, so I pulled up the carpets and also looked at the battery, but everything is dry. Suggestions?

    combo.jpg
    IMG_20200701_135056_DRO.jpg
    1991 MR2 NA | 1988 M5 | 2000 740i Sport | 2004 M3 |
    2009 SMART | 2006 S2000 | 2005 120i | 2006 S500

  3. #3
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    A bad crankshaft position sensor would certainly make the engine run poorly. How many miles/kms on the car?

  4. #4
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    Agreed, but would it set off the other errors? Just over 170k km on the car. Also of note: the first error was for one CPS (plus DSC, etc.); only got the second CPS error later.
    1991 MR2 NA | 1988 M5 | 2000 740i Sport | 2004 M3 |
    2009 SMART | 2006 S2000 | 2005 120i | 2006 S500

  5. #5
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    The CPS and DSC are not connected in any way. The DSC to DME interface could be any number of things. Did you clear the codes, take the car for a drive and rescan? If the CPS code shows up buy a new sensor made by the manufacturer that supplied the sensor to BMW. Aftermarket sensors suck! Replacing it is likely to be a pain so you’ll want to do it only once.

  6. #6
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    Could it just be low voltage? Or the DME relay? Did try clearing the codes and driving, but they came back. Car's almost undrivable. I'll see about the sensors in the morning. Thanks!
    1991 MR2 NA | 1988 M5 | 2000 740i Sport | 2004 M3 |
    2009 SMART | 2006 S2000 | 2005 120i | 2006 S500

  7. #7
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    Further detail, in case anyone's still following....

    No warning lights at all on start up. Car actually starts reasonably well when cold. Revving past about 2100 gets really rough and sets off all the warning lights in the picture. Gets slightly smoother at around 2500 and then fuel cut eventually (high if not under load, 3000 if under load).

    Since all the warning lights come on together (and go away after stopping the engine), and only when the problem manifests, this really doesn't seem like a CPS issue, since the current being supplied via the alternator is regulated. Instead, it seems like this must be voltage supply or module related.

    I've looked in every spot and can't find any evidence of water, but I must have missed something since the rain shower was the only variable. Didn't find any water or any circuitry in the trunk near the battery or on the sides. Any other ideas or places to check? The FRM has had issues in the past, so could it be messing with the engine managment? Can I unplug it or remove a fuse or two to test?

    IMG_20200703_180616_DRO.jpg
    1991 MR2 NA | 1988 M5 | 2000 740i Sport | 2004 M3 |
    2009 SMART | 2006 S2000 | 2005 120i | 2006 S500

  8. #8
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    Given all the various seemingly random codes, this does seem to be voltage/ground related.....if your alternator is good, then I'm thinking you have a serious ground fault somewhere, maybe it only shows up once the revs build because the ignition system is introducing more noise into the system at that point causing things to go wrong...

  9. #9
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    Concur with kneecaps. Get a digital volt meter and check the voltage at the jumper post located under the red plastic cover under the hood. Use the engine as the ground/earth. Check it when the engine is:
    - off
    - idling when cold
    - idling when hot
    - revving at 2000rpm.

    Also, switch the meter to read alternating current (ac). Check the voltage when the engine it idling. There should be zero ac. I did this on a friends old Nissan and the alternator was putting out 37vac! That fixed a bunch of odd electrical issues.

  10. #10
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    Quote Originally Posted by MarcoZandrini View Post
    Concur with kneecaps. Get a digital volt meter and check the voltage at the jumper post located under the red plastic cover under the hood. Use the engine as the ground/earth. Check it when the engine is:
    - off
    - idling when cold
    - idling when hot
    - revving at 2000rpm.

    Also, switch the meter to read alternating current (ac). Check the voltage when the engine it idling. There should be zero ac. I did this on a friends old Nissan and the alternator was putting out 37vac! That fixed a bunch of odd electrical issues.
    I can also personally vouch for a voltage issue when my alternator was dead/dying, I was able to drive for many miles on my E46 with all kinds of scary "random" codes coming up, gear box limp mode and everything you can imagine. Only realised the alternator was kaput when she finally died on me.

  11. #11
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    update

    Thank you both for your replies. Should have updated this post a while back, but haven't had the time. Was almost certain it was voltage related because, agreed, it sure sounds like it, plus everything seemed fine the day before and then in the morning, after a thunderstorm, it wasn't. But ... it turned out to be the crankshaft position sensor all along, as well as an ignition coil pack (the latter of which I replaced once I swapped out the crankshaft sensor and could see that error clearly). Due to being on the road and not having easy places to work on the car, I tried everything else I could think of before getting to the sensor. So it turns out the crankshaft position sensor can indeed cause all kinds of electrical gremlins (including, e.g., setting off the tire pressure monitor warning on a car without that option). Here are the main things I tried, in case anyone else ends up in the same boat:

    1. Tested alternator and battery voltage
    2. Disabled modules via fuse: FRM (F36, F41, F53, F52), TPMS (not optioned; F24, F27), DSC (F31, F65, F20)
    3. Removed JBM for inspection (car won't run without, so couldn't test that scenario)
    4. Removed FRM for inspection and tested car without
    5. Replaced DME relay
    6. Inspected ebox and fuses


    As for what caused the failure, probably age and just a coincidence it happened the morning after a thunderstorm. It's possible the sensor strained the coil and caused those failures (not replacing spark plugs regularly can strain coils, so it's plausible), it's possible driving three or four hours with the failed sensor strained the coil, and it's also possible the failing coil and caused the crankshaft sensor to go off (although that's less likely). In the middle of this, I accidentally left the key in the slot and drained the battery, so now the car has a new battery. Also replaced the other three coils and all the plugs for good measure. Runs beautifully now.
    1991 MR2 NA | 1988 M5 | 2000 740i Sport | 2004 M3 |
    2009 SMART | 2006 S2000 | 2005 120i | 2006 S500

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