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Thread: 533i Motronic Ignition Problem

  1. #1
    Join Date
    Nov 2016
    Location
    Olympia, WA
    Posts
    47
    My Cars
    1986 635Csi, 1981 320i

    533i Motronic Ignition Problem

    1984 533i


    Symptom: Running on 5 cylinders.


    Plugs are good; wires are good (check at about 5k ohms per wire, and are newish wire set).


    Removing #3 wire from distributor cap shows no significant spark present at #3 ignition wire terminal on the distributor cap. Tiny spark is present capable of jumping less than 1/16" to a probe grounded at other end and held close to the cap's #3 output terminal.


    Other 5 terminals are supplying very strong spark able to jump nearly 1/2" to the grounded test probe on every other cylinder terminal.


    Cap appears perfect visually (inside and out) and resistance from #3 terminal to inside brass contact is ZERO Ohms. New Bosch rotor installed (old one showed some deterioration), but no difference.


    My theory is that the distributor cap may have an internal fault allowing the spark to be dissipated/shorted out.


    Only way to test the theory is to substitute a new cap, which I don't now have.


    Others say that the problem is NOT the cap, but in the "crank sensors." But as I understand the basic early Motronic system is that there are two sensors on the bell housing, one of which is the TDC sensor that produces only ONE pulse per entire crankshaft revolution and produces that pulse when #1 piston is TDC. The other sensor is the RPM sensor, and it produces one pulse as each tooth on the flywheel passes under it.


    If that is the case, there is no "special" pulse made by either sensor that corresponds to every cylinder's TDC, so I don't see how a bad sensor or trigger tooth would cause only ONE cylinder (in this case #3 cyl) to not have a spark.


    Could someone clarify Motronic ignition triggering or timing for me so I can make an intelligent diagnosis?


    Thanks,
    Bob

  2. #2
    Join Date
    Jul 2020
    Location
    Reynosa, Tamaulipas, Mex
    Posts
    2
    My Cars
    1984 BMW 533i
    I don't know if you ever got around to fixing this issue with your car, but I am having the exact same problem with the exact same car. Would really appreciate it if you could give me some insight.

    Thanks in advance

  3. #3
    Join Date
    Nov 2016
    Location
    Olympia, WA
    Posts
    47
    My Cars
    1986 635Csi, 1981 320i
    See PM

  4. #4
    Join Date
    Jul 2020
    Location
    Reynosa, Tamaulipas, Mex
    Posts
    2
    My Cars
    1984 BMW 533i
    Okay

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