Odd Misfire Problem, Seeking Help

[Bailey4200]

Hey everyone,

Ive got an I6 that recently started a weird misfire problem. About one out of every 3 times i start my truck it will have a misfire. When it does have the misfire i can turn it off and start it up and it is still there. Once i drive the truck a bit and it gets completely warm, i can shut it off and let it sit for a few minuites and it no longer misses the next time i start it. It does throw the SES light when misfiring. Im thinking by what I have read that it may be one of the coil packs starting to go out on it. When they fail do they ever randomly quit working like in my case or is it an all or nothing type of thing? Replaced the plugs with factory ac-delco about 20,000miles ago along with the plug boots. Any input would be appreciated, cylinder 4 coil is looking a little rusty but no water or oil in any of them that i can see. Thanks!

 

[bore_pig]

If you can get the code for us that would be very helpful. I assume you are talking about the 41-103 iridium plugs, they're the good ones. For curiosities sake, how long since you cleaned the throttle body?

 

[Wooluf1952]

Getting the code will help.

Hey everyone,

Ive got an I6 that recently started a weird misfire problem. About one out of every 3 times i start my truck it will have a misfire. When it does have the misfire i can turn it off and start it up and it is still there. Once i drive the truck a bit and it gets completely warm, i can shut it off and let it sit for a few minuites and it no longer misses the next time i start it. It does throw the SES light when misfiring. Im thinking by what I have read that it may be one of the coil packs starting to go out on it. When they fail do they ever randomly quit working like in my case or is it an all or nothing type of thing? Replaced the plugs with factory ac-delco about 20,000miles ago along with the plug boots. Any input would be appreciated, cylinder 4 coil is looking a little rusty but no water or oil in any of them that i can see. Thanks!

Yes, the coil can randomly mis-fire before going completely bad.

It could also be a bad connection or wire.

If you get the code, you can swap coils and see if the miss moves to a different cylinder.

 

[Dshow]

This is a very good site, check this out -> (I6 misfire diy diagnosis - step 1 - ignition)
http://gmtnation.com/f40/superstars-how-videos-thread-229/#post10411

 

[Bailey4200]

thank you for the info, I will work on getting the code and start from there. Luckily I just bought a saab 9-3 for my daily commutes so the envoy can now just be my toy.

 

[Nizar]

Hey everyone,

Ive got an I6 that recently started a weird misfire problem. About one out of every 3 times i start my truck it will have a misfire. When it does have the misfire i can turn it off and start it up and it is still there. Once i drive the truck a bit and it gets completely warm, i can shut it off and let it sit for a few minuites and it no longer misses the next time i start it. It does throw the SES light when misfiring. Im thinking by what I have read that it may be one of the coil packs starting to go out on it. When they fail do they ever randomly quit working like in my case or is it an all or nothing type of thing? Replaced the plugs with factory ac-delco about 20,000miles ago along with the plug boots. Any input would be appreciated, cylinder 4 coil is looking a little rusty but no water or oil in any of them that i can see. Thanks!

i have the same symptoms but its just for 1 minute then every thing is fine plus no ses !! it was bad coil or bad spark ?
thanx

 

[Bailey4200]

Problem Solved, thanks for the help. It was throwing the code p303 which was saying cylinder 3 was misfiring. I took off the intake and tapped on the #3 coil pack and the miss went away, tapped again and it was back. Coil pack was failing, replaced with oem delco from local parts yard for $20 and runs like a champ. I do not usually buy used but i couldnt pass up the $20 part as it looked new and fixed my problem.

 

[Wooluf1952]

Another win for GMT Nation. :wootwoot: