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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.

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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.

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