How do I fix random misfiring
Thread Starter
CF Beginner
Joined: Jun 2024
Posts: 28
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did you follow the procedure in the service manual?
It covers just about everything you need to know.
https://charm.li/Chevy%20Truck/1999/...alance%20Test/
It covers just about everything you need to know.
https://charm.li/Chevy%20Truck/1999/...alance%20Test/
Super Moderator
Joined: Feb 2017
Posts: 6,207
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your fuel trims are going to be wacky as long as there is misfiring happening. You should stick to basics until you sort that out.
Spark plug gap: https://charm.li/Chevy%20Truck/1999/...%20Plug%20Gap/
Spark plug gap: https://charm.li/Chevy%20Truck/1999/...%20Plug%20Gap/
Thread Starter
CF Beginner
Joined: Jun 2024
Posts: 28
Likes: 2
Thread Starter
CF Beginner
Joined: Jun 2024
Posts: 28
Likes: 2
Consolidated updates
I have now
cleaned air filter
Cleaned MAF sensor
Cleaned throttle body
Cleaned IAC valve
replaced spark plugs
Replaced fuel injectors
replaced in line fuel filter
cleared fuel trims
replaced u bolts
Replaced door pins
tested compression (105 psi min, 111 psi on highest cylinder)
Tested fuel balance with new injectors (53 charged; 45 after firing on all)
The fuel trim remains at +5% on idle amd goes up to +35-40% on acceleration.
idle is smooth. I assume I will still hit a misfire when towing due to high fuel trims.
Does anyone have any thoughts?
cleaned air filter
Cleaned MAF sensor
Cleaned throttle body
Cleaned IAC valve
replaced spark plugs
Replaced fuel injectors
replaced in line fuel filter
cleared fuel trims
replaced u bolts
Replaced door pins
tested compression (105 psi min, 111 psi on highest cylinder)
Tested fuel balance with new injectors (53 charged; 45 after firing on all)
The fuel trim remains at +5% on idle amd goes up to +35-40% on acceleration.
idle is smooth. I assume I will still hit a misfire when towing due to high fuel trims.
Does anyone have any thoughts?
Thread Starter
CF Beginner
Joined: Jun 2024
Posts: 28
Likes: 2
Regarding the fuel injector balance testing/results, I have zero experience in this area.
Regarding the pictures of the spark plug(s), what I see sure looks like a way too wide gap.
According to the information off of rockauto.com, the factory recommended spark plug is the ACDelco 41-962 double platinum plug, and the factory recommended gap is 0.040". I do know that the Vortec engines are really picky about which spark plugs they like, so be sure and go with ACDelco 41-962 double platinum plugs. Also, do not purchase them from Amazon or ebay as they will likely be counterfeit plugs. If you want to save a few bucks on plugs, purchase them from rockauto.com as they use the same auto parts warehouses the brick and mortar parts stores use.
If you purchase new spark plugs, DO NOT check the gap or attempt to regap them. They come pre-gapped from the factory and if you try to check/adjust the gap, you can easily damage the precious metal coating on the electrodes as it is extremely thin.
Regarding the pictures of the spark plug(s), what I see sure looks like a way too wide gap.
According to the information off of rockauto.com, the factory recommended spark plug is the ACDelco 41-962 double platinum plug, and the factory recommended gap is 0.040". I do know that the Vortec engines are really picky about which spark plugs they like, so be sure and go with ACDelco 41-962 double platinum plugs. Also, do not purchase them from Amazon or ebay as they will likely be counterfeit plugs. If you want to save a few bucks on plugs, purchase them from rockauto.com as they use the same auto parts warehouses the brick and mortar parts stores use.
If you purchase new spark plugs, DO NOT check the gap or attempt to regap them. They come pre-gapped from the factory and if you try to check/adjust the gap, you can easily damage the precious metal coating on the electrodes as it is extremely thin.
Super Moderator
Joined: Feb 2017
Posts: 6,207
Likes: 689
well don't feel bad. without diagnosis, the chances of fixing a problem by throwing darts at the parts dartboard are pretty slim. You could have just as easily been wrong, and still be replacing half the sensors on the engine.
Thread Starter
CF Beginner
Joined: Jun 2024
Posts: 28
Likes: 2
Thanks, at least it got fixed and got itself a nice little tune up