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Thread: Random Misfires

  1. #1
    VXRed
    Join Date
    4th October 2013
    Posts
    108

    Default Random Misfires

    Hi folks,

    I was sitting at the traffic lights when the car started to misfire all over the place on idle and under acceleration, engine/service lights lit the dash up like an xmas tree.

    I pulled over, turned the car off , checked vac lines, air filter, coil pack connector (it popped off when coming off the motorway in the past!), oil filter cap, dipstick etc... but nothing was out of place.
    after much swearing and head scratching I cranked it back up, the lights disappeared and the engine was running smoothly. It has been fine for 20 miles under load, no warning lights or misfires.

    I put in a new coil pack 4K miles ago due to constant misfires under load with new plugs (OE) put in 2K miles ago, so I doubt it could be that and I've ordered a new MAF as I have intermittent hunting issues on Idle.

    For the life of me I just can't understand what that misfiring was about, anybody else experienced anything like that or any thoughts?

    Note: Engine is forged and running with a K03 Hybrid with aftermarket actuator and recirc amongst other things

  2. #2
    VXRed
    Join Date
    8th August 2016
    Posts
    54

    Default

    The most common causes of engine misfires are: worn spark plugs, weak fuel injector, vacuum leak, worn valve seals, carbon tracking, and no voltage at the coil. Do you know what is happening when its misfiring ie. Heavy vibrations, loss of power, and staggering jerks at low revs. If for instance its a fuel related misfire a leaky injector will make one cylinder run really rich so it will run OK with normal loads , but idles rough, maybe some whitish smoke, smells like fuel in the exhaust.

  3. #3
    VXRed
    Join Date
    4th October 2013
    Posts
    108

    Default

    Quote Originally Posted by SimonVX View Post
    The most common causes of engine misfires are: worn spark plugs, weak fuel injector, vacuum leak, worn valve seals, carbon tracking, and no voltage at the coil. Do you know what is happening when its misfiring ie. Heavy vibrations, loss of power, and staggering jerks at low revs. If for instance its a fuel related misfire a leaky injector will make one cylinder run really rich so it will run OK with normal loads , but idles rough, maybe some whitish smoke, smells like fuel in the exhaust.
    Definite loss of power, exhaust note changes, car jerks and it just sounded like spluttering.

    I have 395cc Bosch injectors and for the past few thousand miles they have been making a very loud ticking noise which changes with the revs (separate from the usual valve train noise I'm used to) - definitely a noticeable smell of fuel from the engine bay from time to time and the exhaust but no white smoke...

    I'm putting the new MAF in over the weekend and keeping a spare coil pack in the boot I hope this will remove the intermittent hunting issue I have. If not I will need to investigate the fuelling.

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