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M42 Ignition/Coil Packs Problem

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    M42 Ignition/Coil Packs Problem

    My m42 is running strong but I am baffled concerning the main problem with the engine. Currently the car runs and drives pretty good with this arrangement but does have a major problem.

    pin 24 off DME = cylinder 1
    pin 25 off DME = cylinder 3
    pin 51 off DME = cylinder 2
    pin 52 off DME = cylinder 4

    I have checked the pinouts of the DME to confirm this 4+ times now and Im baffled because according to every wiring diagram online...

    pin 24 off DME = cylinder 3
    pin 25 off DME = cylinder 1
    pin 51 off DME = cylinder 4
    pin 52 off DME = cylinder 2

    the car WILL NOT START with the plugs hooked up this way. no way in hell. its very weird. will crank endlessly without a sputter or anything.

    so mine are mixed up yet the car pulls pretty strong. it coughs and sputters/misses like crazy high in the revband at WOT around 5500 sometimes 6000. almost seems like fuel related but the car has s52 pink top injectors (flow the same as stock) that have been rebuilt and I have tested each one's spray pattern on car. fuel pressure Ive driven around with a gauge and the fuel pressure does not change when the miss occurs.

    I am running an unknown condition AFM off a junkyard e36 m42 (carries same part # in realoem as e30 m42 however the AFM has a different bosch number on it). this could be the cause of the issue, but I have tried 3 afms all together (2 junkyard e36 and one questionable e30 one) and issue is always there.

    brand new spark plugs and ignition wires, both NGK. coil packs all test good and are newer bosch ones. new BMW OE crank sensor and facet brand cam sensor.

    I am curious if anybody else could pinout their m42 car for me similar to I have done or have any insight. thank you!
    Last edited by 5Toes; 11-28-2015, 03:35 PM.

    #2
    Got this?



    Everything checked out using this as a reference when I built my MS setup. I have a COP ignition setup. Maybe someone re-wired yours at some point?

    If it's running on all cylinders at any time it's not a wiring mixup causing your miss. A 4 cyl won't run on all cylinders if you mix up any of the plug wires and if you mix the wrong ones up it will cough and bang and shoot fire out of the intake.
    Last edited by varg; 11-28-2015, 08:22 PM.

    IG @turbovarg
    '91 318is, M20 turbo
    [CoTM: 4-18]
    '94 525iT slicktop, M50B30 + S362SX-E, 600WHP DD or bust
    - updated 1-26

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      #3
      ^ thanks for the insight. this engine runs on 2 cylinders believe it or not it doesnt even come close to dying if I pull off two plug wires with it running.

      the chart you posted above matches the pinouts that I listed above.

      my main concern is that the firing order is out of order right now. the car either is running lean or something because it seems down on power, and theres a high rpm miss - I believe it to be the AFM since I have been researching the problem for about a week now.

      Im leaning towards the crank pulley being 180 degrees out... this issue is driving me nuts. could someone please pin out their ignition coils real quick like I did and report back?

      Comment


        #4
        It can't be firing wrong and still run. If the crank pulley was 180 out AND the coils were switched, it might run. Trying to wrap my head around that...

        Maybe it's just an M42 and not down on power? lol

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          #5
          it has trouble going up steep at hills pinned WOT in 3rd gear at 3000 rpm.

          something is obviously switched because it is definitely 180degrees out because coils hooked up proper it wont even sputter, with them switched it is running but I think lean. going to remove the harmonic balancer pulley thing and check it out as well as get the afm rebuilt

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