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4.3 Silverado random misfire severely at 200+ temp


Peachesandherb

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My 2005 Silverado 4.3 vin X will run great till it reaches higher than 200ish. I've replaced crank, cam sensors, plugs, wires, coils, ignition module and some other parts. My buddy has a gm scanner and found no real problems. My codes are p0300 random mult misfire and evap. In 20min of run time at 210 temp it picked up 970 misfires in cyl 6 and around 600 in cyl 3. After awhile cyl 1 started misfiring and got up to around 200. My guy with the scanner started disabling injectors and when he got to cyl 6 it made no difference he said but that's all he could find. My fuel pressure key on engine off was 55 with no leaking after key was off

 

Also, heads were redone already, new coolant temp sensor, cap and rotor, no cats due to them being clogged when I purchased it. 80k miles.

 

I don't understand how it can run great til it's warm then just crap out when it's warm, especially with his recommendation of replacing the poppets/injectors since he believes they are the problem.

 

Any other ideas?

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My 2005 Silverado 4.3 vin X will run great till it reaches higher than 200ish. I've replaced crank, cam sensors, plugs, wires, coils, ignition module and some other parts. My buddy has a gm scanner and found no real problems. My codes are p0300 random mult misfire and evap. In 20min of run time at 210 temp it picked up 970 misfires in cyl 6 and around 600 in cyl 3. After awhile cyl 1 started misfiring and got up to around 200. My guy with the scanner started disabling injectors and when he got to cyl 6 it made no difference he said but that's all he could find. My fuel pressure key on engine off was 55 with no leaking after key was off

 

Also, heads were redone already, new coolant temp sensor, cap and rotor, no cats due to them being clogged when I purchased it. 80k miles.

 

I don't understand how it can run great til it's warm then just crap out when it's warm, especially with his recommendation of replacing the poppets/injectors since he believes they are the problem.

 

Any other ideas?

 

Did you replace all the parts trying to correct this issue? If you did, how did you determine they were faulty? It is quite possible that the injectors are acting up at specific temps only, they have moving parts in a close tolerance environment, Another possibility is a vacuum leak at a specific temp as well.

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