I have a check engine light and a generic 0304 #4 cylinder misfire. I have replaced the plugs, wires and now coil pack but the light reappears. I am a good mechanic but on construction equipment. What would be my next move? Fuel injector?

  • the injectors aren't known for failing, but it might be. try swapping the injectors around. i've seen more of these with compression issues. use a 194 bulb or a noid light to check the injector signal. another thought would be carbon buildup on the intake valve.
    – Ben
    Nov 18, 2016 at 2:57

1 Answer 1


Misfires are usually caused by one of 3 things:

  • poor/no spark: you've addressed most of this with spark plugs and cables. Grab a timing light and make sure you are getting steady evenly spaced spark on each cylinder.
  • no/not enough fuel: test your fuel injectors with a multimeter and measure your fuel pressure too.
  • low/no compression: do a compression test on all 4 cylinders, make sure they are even and close to spec.

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