2004 GMC Envoy Misfire on #4 Cyl.

NOVA2037

MEMBER
2004 GMC ENVOY
4.2L
6 CYL
2WD
AUTOMATIC
220,000 MILES

2 weeks ago truck was missing on #4, checked and found water and oil around sparkplug. Replace plugs #4 coil valve cover and intake gaskets. Found a new design weather strip at dealer to kept rain water off engine. Ran fine. Now its back with miss at idle only. I check spark, compression and injector balance, all test fine. Found a tip on internet about variable cam timing actuator issue. Took it out, cleaned and tested it. No change. Looked in cylinder with bore scope, see no water or other concern. What next?

2 Replies

HMAC300

MECHANIC
48,601 POSTS

Check for a vacuum leak and or compression. Then look at it misfires are very hard to find nowadays and can be a sensor bad someplace on engine.

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Thursday, February 12th, 2015 AT 5:58 AM

KEN L

MASTER CERTIFIED MECHANIC
47,513 POSTS

To me it sounds like the spark plug got cracked during installation, I would remove the spark plug and replace it with another. Here is a guide to help you do the job correctly.

https://www.2carpros.com/articles/how-to-change-spark-plugs

Here is the spark plug

Spark Plug Type .................... AC 41-981

Heck if it has been a while I would replace all of the spark plugs. Check out the images (below). Please let us know what happens.

Images (Click to make bigger)