2007 Hummer H3 • 91,000 miles

The Hummer dealer suggested that it was time to work on the fuel injection system, so I approved the work. One week later the H3 started idling with a slight shake once in a while, and then displaying the Check Engine Light. The light would turn off and car felt fine for a couple of weeks. It has done this 3 times and the diagnostice test says it's a P0303 misfire in cylinder 3. The dealer says it has nothing to do with the Fuel Injection system work they did, and suggested that they needed to tear down the top engine to fix the problem (over $2000). I refuse to go back to the dealer and want to know if changing the sparkplugs is a good place to start?

Thank you
December 18, 2012.

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