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Possible Causes of intermittent Loss of spark

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    #16
    did some further checks. with test light on +12V of the coil connector the incandescent test light went out as engine cutout but came back on a second o two after it stopped running( it seemed to coincide with the fuel pump witching off). perhaps a coincidence? i'm starting to suspect a possible intermittently bad +12V switched ignition circuit (in particular a dodgey wire to the coil). i wonder if the fuel pump is somehow related.

    if only it would fail consistently so i could do a test and repeat it several times to confirm behaviour. this contradicts what i saw with the cranking a day or so ago but that was with a LED test light.
    Last edited by digger; 09-01-2019, 04:14 PM.
    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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      #17
      can confirm the coil +12V ignition switched supply is intermittently dropping out. rigged up a test light. presumably a bad wire/ connection

      whats the best way to isolate ? just trace back? given everything else on ignition switch feed still works its probably relatively localised to the coil and not a wider issue with the circuit
      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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        #18
        So the positive battery supply at coil was dropping out intermittently but the supply green 2.5 wire near battery tray direct from pin 7 of c101 did not. The PO had installed an alarm and the coil supply was cut and routed to an alarm. I bypassed that and seems to be running like a champ.

        Oddly enough alarm has never been used in the last 15 years and has never given a problem in it's supposed disconnected state. So I don't know if it was bad connection in the alarm harness or something to do with actual alarm. Nevertheless it's been bypassed now.
        89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

        new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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          #19
          One of those wires (I don't remember which) is shielded. Some of the shielding might have been in the splice causing an intermittent ground.

          RISING EDGE

          Let's drive fast and have fun.

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            #20
            I don't think coil positive would be shielded?
            89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

            new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

            Comment


              #21
              You're right, the 2.5 GN from the C101 is not shielded. The other one (pin 1 from the DME and the diagnostic connector, which is I guess the signal wire) is shielded.

              RISING EDGE

              Let's drive fast and have fun.

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