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2002 gmc envoy_slt
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4 Posts
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OK so our 2002 GMC envoy just started misfiring really bad. Ses light is on for code p0304 misfire cylinder 4. Changed all the plugs and found a pool of oil on top of plugs 3 and a lot on top of plug 4 (from front) . I cleaned all of the oil up best I could and also changed the coil gaskets. Changed the plugs and ses came back on p0304. I'm thinking it has to be coil or injector right? Can I swap plugins on coils to see if it changes cylinder?
 

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2005 chevy trailblazer_ls
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56 Posts
misfire

Don't change connectors unplug the coil and change it with a diffrent cylinder and see if the misfire follows the coil
 

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2002 chevy trailblazer_ltz
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3,250 Posts
The "oil" you got on those 2 cylinders is not oil....it's a mixture of mostly water and a little oil mixed in...it comes from water (rain or car wash) running off the cowl onto the top of the engine.....the cowl edge is right above those cylinders. The water is shorting the plug out.

A piece of 3/8" foam weatherstripping put under the rubber cowl seal should fix it.

As for the coil pack, replace # 4.
 

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2002 gmc envoy_slt
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So I'm new to this site and hope I'm not posting this incorrectly. My 02 envoy is misfiring on #4 cylinder and the ses light begins to flash at about 30mph then goes away. I have swapped the coil with another one from the 2nd cylinder the scan tool comes up the same p0304 (misifre cylinder 4) leading me to believe it's not the coil. Replaced the plug and boot with no affect. I have also tested the wiring for the coil and am getting almost 12v. I did not notice any oil or water on the plug when I changed it out but will take a closer look after work. Whats the best way of testing the injector if water shorting out the plug is not the problem?
 
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