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Denali 6.0L P0300 Random Misfire

Discussion in 'Any Other Gas Engine' started by whatnot, Sep 24, 2008.

  1. whatnot

    whatnot Member

    May 1, 2008
    Waunakee Wisconsin
    My dad had an '02 GMC Sierra Denali with 6.0 liter that has been getting a random misfire code. Sometimes it flashes the SES light while driving.
    So far the fuel and air filters and spark plugs were changed and the MAF was cleaned.
    Is there a common cause for this or is it going to be a lot of parts replacing?
    Also, it sounds like it might have a small exhaust leak. Can that possibly cause the misfire?
  2. ockgator

    ockgator New Member

    Apr 14, 2009
    hook up a scanner and look at misfires, should show current and history misfire... you want to look at the history #'s
  3. oldbrownsierra

    oldbrownsierra The Weekend Mechanic

    Dec 17, 2009
    Check all plug wires. After being replaced, or replacing plugs, they tend to pop off for the first while. Mine did for about 6 months, and has been fine since.
    Last edited: Dec 21, 2009
  4. Dad's 05 LLY

    Dad's 05 LLY Real Trucks Don't have Spark Plugs!

    Jul 6, 2008
    Lakeville, Minnesota
    I'd replace the wires. They're relatively cheap, and one more variable eliminated. Be sure you use di-electric grease on the boots. I like the Beldin Premium wires from NAPA.
  5. whatnot

    whatnot Member

    May 1, 2008
    Waunakee Wisconsin
    He took it to the dealer and they said it is the injectors. They cleaned them and said there were a couple that were still misfiring. They told told him to drive it for a while and if they don't clear up then they will have to be replaced. It has been quite a while since then so he will have to get them replaced.

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