Denali 6.0L P0300 Random Misfire

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

  1. whatnot

    whatnot Member

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    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

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    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

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    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!

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    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

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    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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