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P0304 code help

Discussion in 'Chevy Trucks' started by WOODY367, Dec 2, 2015.

  1. WOODY367

    WOODY367 Senior Member
    from LI, NY
    Messages: 477

    I have a 99 Yukon and was on a road trip, when I was going up hill in the mountains the service engine light can on flashing and then steady. I put the code reader on and came up with code P0304 " #4 misfire" I cleared the code and it was fine all week. I took the same route home and when I was going uphill in the same place the light came on again with the same code. Any thoughts what it might be?
  2. Rick547

    Rick547 Senior Member
    from Indiana
    Messages: 537

  3. unior

    unior Member
    Messages: 32

    Could be a lot of things. Spark plug, wires, coil pack, valve damage.
  4. maxwellp

    maxwellp PlowSite.com Addict
    Messages: 1,123

    Faulty spark plug wire
    Faulty coil (pack)
    Faulty oxygen sensor(s)
    Faulty fuel injector
    Burned exhaust valve
    Running out of fuel
    Poor compression
    Defective computer

    I would pull # 4 plug and have a look.
  5. WOODY367

    WOODY367 Senior Member
    from LI, NY
    Messages: 477

    Thanks guys, I will check it out this weekend. It is running fine now it just happened when going up the mountain on my 650 mile trip. I was 500 miles into it when it append.I oly did a full tune up 40,000 mules ago. This truck only has the 1 coil on the HEI distributor.
  6. ThatGuySnowPlow

    ThatGuySnowPlow Member
    Messages: 62

    As soon as I get any misfire codes I change everything... Cap,rotor,coils if more than one or individual. Nothing more I hate worse than chasing down bad coils etc.... Another thing is a bad intake gasket can cause misfire codes as well, Just had this happen on a ford pickup and never knew it could.