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E30 – Misfire

This topic contains 3 replies, has 2 voices, and was last updated by EricTheCarGuy 1 EricTheCarGuy 1 week, 3 days ago.

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  • #1001786
    jmorgan456
    jmorgan456
    Participant

    I have a 1987 E30 BMW — 325e
    I have been trying to get it recommissioned after a 10 year sleep. I rebuilt the engine from a longblock and it was running OK – decently even after I got it refreshed. But recently it developed a misfire that I cannot diagnose and I am running out of ideas.
    So, the cap, plugs, rotor, and wires all new. Injectors cleaned and rebuilt. I know there is rust in the tank, but I have cleaned the in tank screen and there is a brand new fuel filter on the car. Fuel lines are clean and new fuel in tank.

    I checked the wiring for the fuel injectors today – thinking I might have swapped – that is fine. Basically, it misses and stumbles with load. Seems to even out at higher revs – but that could be my imagination.

    Thoughts…? Help.

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  • #1001960
    EricTheCarGuy 1
    EricTheCarGuy
    Keymaster

    Often overlooked is the mechanical condition of the engine. Even though you replaced the long block there could still be issues. I would recommend starting with a compression test and if you find low compression in one of the cylinders, follow up with a leak down test. I would also recommend checking the timing components to make sure they are secure and in time. If you’re off a tooth, or if the timing components are loose it can cause a misfire. That way you can rule out a mechanical issue as the cause of the problem.

    More info here: http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

    Good hunting.

    #1002135
    jmorgan456
    jmorgan456
    Participant

    I replaced the timing belt and I checked compression before replacing the head.
    The block was amazing. Factory crosshatch still on cylinders. The head has been heat cycled a few times, so perhaps I should do a valve job?

    #1002141
    EricTheCarGuy 1
    EricTheCarGuy
    Keymaster

    Just because the compression was good before you started doesn’t mean it’s good afterward. Anytime you have issues after major work like that, something you did is the most likely cause of a problem. That’s not a personal dig against you, it’s just the most practical explanation, and a good place to start a diagnosis.

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