What is the most likely cause of an engine cylinder intermittently failing to fire.?

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  • 2 years ago
    Best Answer

    Bad coil, worn plug wire, clogged fuel injector, corroded distributor cap, low compression, blown head gasket, intake port leak etc, and the list goes on. Depending on the vehicle vintage since you didn't post no info? On many new engine designs, it would likely be a bad coil on plug ignition module type issue or the associated misfire cylinder piezoelectric fuel rail injector unit. If you can pull the injector wire while running, and see little to no difference with good spark, it's time to pull the fuel rail and swap the injector out.

    You can check the spark with an inductive timing light if you have plug wires, you will need an oscilloscope to test the 5VDC trigger.

    You should see a nice SCR sawtooth or shark fin half wave for the ignition and fuel injector 5V pulses on the oscilloscope screen.

    To the lubix commentator, an SCR is the silicon controlled rectifier that sends the regulated 5VDC trigger pulse from the PCM/ECM module to the active engine sensors, ignition coils, and fuel injectors. You could have just Doogled SCR to find out what it means :/

    https://www.youtube.com/watch?v=MnnCzKNLGoI

    Youtube thumbnail

    • Lv 5
      2 years agoReport

      What the Hell is an SCR sawtooth half wave? An SCR is a solid state device, the sawtooth triangle wave is usually from an old points ignition. Many new ignitions don't use an SCR, anyway. A half wave is a 180 degree wave form from a diode rectifier---the voltage to the coil is not rectified.

  • 2 years ago

    There are a few dozen most likely causes. A worn out spark plug, not enough compression due to a leaky gasket, not enough fuel due to a sticky fuel valve, not enough air due to a sticky air valve, a faulty connection somewhere between the electrical source and the spark plug (which is about two dozen places right there), or just about anything else.

    Yes, yes that is a long list of maybe-possibly. But that's what you asked, and the answer is maybe just about anything. That's the best you can get when asking total online strangers.

    You do know that a certified mechanic can diagnose the problem and eliminate the maybe-possibly factor within an hour or two, right? Just a suggestion.

  • 2 years ago

    lack of fuel and or spark

  • 2 years ago

    Bad ignition

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  • Fred
    Lv 7
    2 years ago

    How many kms (or miles) has the car done since the spark plugs were changed. It could be a burnt spark plug and you should start with the simple things first.

  • Mr.357
    Lv 7
    2 years ago

    Bad spark plug.

  • 2 years ago

    Spark plug...change them all.

  • don r
    Lv 7
    2 years ago

    Most likely a worn out spark plug, or bad wire.

  • 2 years ago

    It depends on what the engine is in. If it is from the 1970s it will be a bad distributor cap, spark plug wire or spark plug. If it is more recent, add fuel injectors. More recent yet, remove the distributor cap from the list and add a coil pack instead. Completely modern, remove coil pack and change it to coil on plug. (These are all generalizations, too.)

    However, it is always a mistake to replace parts based on probabilities unless the part is either very cheap and easy to replace and/or is due for replacement anyway. It makes sense to replace all the spark plugs for both reasons, but not to replace coils like that. Shotgunning parts drives up the cost of owning a vehicle. In addition, the cause may be not on the list of top suspects. If the problem is a valve is burned, or there is coolant getting into the cylinder from a bad intake manifold gasket or head gasket, it will only get worse if not identified and fixed.

    • Anon
      Lv 5
      2 years agoReport

      Instead of aft cyl misfire, the Forward cyl now misses. And I cleaned out cats, new plugs, set valves, fresh gas, checked idle cutoff. Weird..

  • Anonymous
    2 years ago

    some systems now switch off one or more cylinders for economy and they will only fire under acceleration or high speed, check the system specs before you waste time and money repairing something that isn't broken usually it's with 6 and 8 cylinder engines

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