454 vortec misfires only when hot

[kevin camps]

driving a 97 k2500 camper special, 4l80e with 454 vortec

 

couple days ago I got in my truck after work and noticed it would stumble when hot, 100C no problem but a little bit warmer and i would have issues. always under load during acceleration. got home and idled in drive and it felt like an obvious misfire, RPM would drop to about 500. pop it in neutral or park and no misfire or stumbling, its been confusing me since in the mornings when i pull it out the garage it has no problems all the way to work (5 minutes highway and 5 minutes city) but end of the day and evening- same issue

 

bought the truck with 268km now has 276, oil change every 5000k.

 

did fuel pump (48psi at idle now) FPR, distributor cap and rotor, plug wires and plugs, ran seafoam through the intake and in the fuel tank.

 

ive heard of distributor gears going south but id assume then i would have the issue when cold too. runs like a top at any temp below 100C, no engine light, plugged the scanner in anyways and no codes whatsoever.

 

any help is appreciated, looked through forums for a couple days now but nothing exactly like what I'm experiencing.

 

kevin,

[Liam the red]

I would check the water temp sensor and the Intake air temp sensor. When they start going south, it sends incorrect data to the PCM, which causes incorrect changes to fuel trim and timing. This could cause your issue.
It doesn't always set a code, because at first the data is not completely out-of-spec, but can cause engine miss.

[kevin camps]

7 hours ago, Liam the red said:

I would check the water temp sensor and the Intake air temp sensor. When they start going south, it sends incorrect data to the PCM, which causes incorrect changes to fuel trim and timing. This could cause your issue.
It doesn't always set a code, because at first the data is not completely out-of-spec, but can cause engine miss.

 

Okay i will give those a try, im currently on a family vacation but will update once im back, is there a easy way for me to test these sensors with a multi meter? electronics is quite a grey area for me since this is the newest vehicle ive owned haha

 

appreciate the help

kevin,

[kevin camps]

On 11/26/2021 at 3:58 PM, Liam the red said:

I would check the water temp sensor and the Intake air temp sensor. When they start going south, it sends incorrect data to the PCM, which causes incorrect changes to fuel trim and timing. This could cause your issue.
It doesn't always set a code, because at first the data is not completely out-of-spec, but can cause engine miss.

replaced both sensors a couple days ago, feels better but still not gone. I’m at a loss haha. My buddy thinks it might be my timing but if it was then I’d have the problem all the time right?