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Thread: Blacktop Misfire Help

  1. #1
    Tyre Kicker

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    Blacktop Misfire Help

    Hey everyone. Have a standard blacktop in a mk2 that is running OMEX 600 ECU and matching ITBs.
    After 2 years of no issues I have delivered a pretty consistent misfire that I am having trouble trying to locate the cause of.
    Happens nearly always on cylinder 4 (closest to the firewall) but have seen it rarely on 3. Never 1 or 2.
    Youtube link looking straight down ITB #4. RS2000 - YouTube At certain revs it is more prevalent 2-3000. Sometimes does it
    lots sometimes everynow and then. Video is on the low end of the frequency range.

    So far have I have plugs, leads, coil pack. I have rotated the injectors to other cylinders with no change.
    Fuel pressure is constant. No errors noted on the ECU. Valve tolerances came in fine, compression test was good.
    All wiring is new as of 2 years ago.

    Hoping for some suggestions on what else I can look at or try to sort this issue..

    cheers

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    Racer Decade Plus User rallyrob's Avatar

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    Re: Blacktop Misfire Help

    Not sure why it would be as it's mainly on 1 cylinder but have you tried changing the crank sensor? Maybe it's just starting to break down.

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    Spanner Monkey

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    Re: Blacktop Misfire Help

    I've seen it on a Blacktop where it was the plug connection going on to the injector. This gave an intermittent misfire that took a bit of finding until a laptop was connected up to it the next day.
    Initial job was swapping the cams for Kent 2002s and there was no issue with the running before I fitted these. Basically, I must have disturbed or hit the plug while swapping the cams.

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    Re: Blacktop Misfire Help

    Also, crank position sensor has been swapped out to test.
    Will have a look at the wiring. That could be something.

    Cheers

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    Re: Blacktop Misfire Help

    Are you running wasted spark? As not a misfire as such as firing whilst the inlet is still open - not a big backfire to indicate bad valve timing but maybe too tight gaps - shim & bucket valve normally wear tighter so no tappetty noise?

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    Re: Blacktop Misfire Help

    Yes to the wasted spark and yes it seems more pre-ignition. The engine ran without issue for 2 years. Pulled the engine as my sump gasket had failed. Back in and running and this problem started. Engine not making any noises different than before. It’s like I have I have caused the issue by pulling the engine out

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