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2004 gmc envoy_slt
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2 Posts
Discussion Starter #1
About a month ago we got a check engine light and very rough idle. The code indicated misfire on cylinder 4. I replaced the spark plugs and cleaned the throttle body, but that didn't help at all. I then replaced coil pack # 4 and it worked fine. I cleared the code and it didn't come back.

A few days ago we had the same issue, except this time the code said it's cylinder 2. I pulled coil pack # 4 to see if the spark plug was cracked or something. It wasn't cracked, but I noticed a bit of oil residue in there (see the pic attached). FYI, that's dielectric grease right on top of the spark plug. I replaced the coil pack, cleared the code, and it's been working fine these past few days. My questions are:

1) Is it okay to have a little oil residue in there?

2) What could be causing multiple coil packs to go bad in such a short time-frame? Could it be related to the fact that I filled the gas tank within a day before each coil pack going bad?
 

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2002 gmc envoy_slt
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33 Posts
The oil residue is probably leaking from the gasket. Not a big problem.

Don't know the mileage of your Envoy but if a few coils have failed, probably more will as well...just part of parts wearing out, IMO.
 

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2002 chevy trailblazer_ls
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4,125 Posts
If the oil wasn't there before then you may not have tightened the hold down bolt enough. It does use the whole body of the coil to compress the gasket. It may also just be a coincidence and normal wear and tear. And as coach said the rest of the coils will soon follow. I'm also currently running 2 new coils but it's been at least 6 months since the last one failed. They failed about a month apart
 

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2002 gmc envoy_slt
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33 Posts
If the oil wasn't there before then you may not have tightened the hold down bolt enough. It does use the whole body of the coil to compress the gasket.
Are you sure about that? IMO, it's the valve cover bolts that hold the gasket in place. The bolt on the coil is to make sure the coil stays on the sparkplug.
 

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Premium Member
2003 gmc envoy_slt_xl
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116 Posts
I carry a spare coil always and at over 200k, I expect the occasional failure. Also carry a cheap Harbor Freight OBD reader which is good for emission, coil and vvt camshaft positioning codes so I can change on the fly. Have tried AC Delco and off brands with no discernible difference.
 

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2002 chevy trailblazer_ls
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4,125 Posts
Are you sure about that? IMO, it's the valve cover bolts that hold the gasket in place. The bolt on the coil is to make sure the coil stays on the sparkplug.
It definitely helps since their is a gasket at every plug. The cover is plastic and fairly wide so I'm sure their is a bit of flex and the coil may help.

Replacing the valve cover gasket calls for like 5 hours so worst case just pull the plug every few months to drain the oil and avoid a misfire.
 
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