2004 GMC Envoy Misfire on #4 Cyl.

2004 GMC ENVOY

220,000 MILES • 4.2L • 6 CYL • 2WD • AUTOMATIC

NOVA2037

MEMBER
1 POST

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?

Feb 11, 2015 at 6:25 PM

HMAC300

✓ASE Certified 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.

Feb 12, 2015 at 5:58 AM

STRAILER

✓ASE Certified Mechanic
54,837 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 enlarge)

Professional Diagram for 2CarPros Members
Click here to log in and view diagram.

Jul 1, 2024 at 6:35 PM

Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.