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Thread: Sudden m20b25 Misfire

  1. #1
    Join Date
    Oct 2024
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    1989 bmw 325i

    Sudden m20b25 Misfire

    Hello all,

    Recently acquired an e30 and really enjoying it. Only issue is a sudden misfire that happens (usually after the car is warm) at random times. All power seems to suddenly drop for a second or two and if the car is not moving in gear it will stall itself.
    It is not rpm depended but i will say it seems to happen more often if you are on the gas hard and then in that case it also backfires pretty hard.

    took the distributor cap off and both the contacts and and rotor seemed to be in relatively good condition. Spark plugs looked good but did have some oil in the threads. Thinking AFM might be to fault but I am not as adverse in working on older cars so I just don't know.

    I was informed of the problem by the seller and the car made the first 150 miles of the drive home perfectly but in the last few miles it started happening quite often

    Any input is much appreciated.

    Thanks,
    Luca

  2. #2
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    Does the tach dive towards 0 when this happens? If so, it's ignition related. If not, it's fuel related.
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  3. #3
    Join Date
    Oct 2024
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    california
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    My Cars
    1989 bmw 325i
    Yes tach drops to a couple thousand rpm when it happens.

  4. #4
    Join Date
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    Regina, Sask, Canada
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    My Cars
    82 320i 89 325i
    failing cps dropping the signal is possible

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