PO 300 Misfire.

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11-11-2009, 06:01 AM

TheTechnician

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PO 300 Misfire.

I have a 2007 GMC Sierra "New body style" 5.3 and I have a misfire on cylinder 8, I have changed the spark plug, plug wire, coil and finally the injector. I have done an injector flush but still a misfire on number 8, anyone have any other tips or ideas as to why this is having a misfire?

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11-11-2009, 07:33 AM

iamkeniff

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stock truck?
do a compression check..did you happen to nick the coil harness where itd receive a poor signal?
plugs gapped correctly?

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11-11-2009, 09:43 AM

LowBlack99

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100k warranty! If its not highly modded that is.

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11-11-2009, 05:53 PM

LS1csherm

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intake been off? over heated? Head gasket? what did the plug look like?

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11-14-2009, 09:24 PM

TheTechnician

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replaced the plug, not sure if it had been gapped right out of the box. used a ACDelco plug. intake has not been off that i know of. didnt check head gasket yet

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