2004 GMC Envoy • 6 cylinder 2WD Automatic • 117,000 miles

2004 GMC envoy SLT 6 cyl 2WD. Took in to change plugs (iridiums)and fuel filter. Brought home and SES came on. Returned vehicle, and the same thing happened again. Took to another shop and they indicated a misfire cyl6, code P306. Checked new plugs and no 6 plug was hard to remove and they noted cross threading in that plug. Did tap and once again, a misfire in cyl 6 with same code. Rechecked all plugs and coil packs switching those around to different cylinders with same result a misfire in cyl 6 with same code. Fuel economy has decreased by 25%. Engine starts immediately but idles roughly with trans in drive with brake depressed. When driving do not notice any miss and no loss of power. Engine does not backfire, or stall and no lurching or hesitation. Put can of seafoam in gas tank and no change. Did compression test and all cyls checked out okay. Any help is appreciated
January 23, 2011.

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