2000 gmc 4.3 misfire

mxracer124 · Jan 10, 2010

Its a 00' sonoma with low idle and runs rough, also at idle to 2000 misfire. He did the in line fuel filter,plugs, wires, checked cap looks good. Any ideas...tps, fuel pump, coil going bad?

boardbysled · Jan 10, 2010

Go get it checked for codes would be the first thing i would do.

Hip · Jan 10, 2010

if you recently did wires and or plugs id check your firing order.:haha:

crash2 · Jan 10, 2010

boardbysled said:
Go get it checked for codes would be the first thing i would do.

More than likely it will set a p0300-p0306 which will only define either what cylinder or random (p0300).

Data will be more valuable though to watch the miss-fires as they progress

Brian H · Jan 10, 2010

My truck is pulling a po300 and po430 code. It only misfires when im at a stead pedal and worse at high rpms. Did a tune up and replace my o2 sensors and no change. Not sure where to go from here.

crash2 · Jan 10, 2010

Brian H said:
My truck is pulling a po300 and po430 code. It only misfires when im at a stead pedal and worse at high rpms. Did a tune up and replace my o2 sensors and no change. Not sure where to go from here.

What are the specs on the rig brian?

mxracer124 · Jan 10, 2010

We did have it scanned...po300 random cylinder misfire. It started the misfire before we changed the plug wires.

crash2 · Jan 10, 2010

mxracer124 said:
We did have it scanned...po300 random cylinder misfire. It started the misfire before we changed the plug wires.

You either have sticky poppets on the injectors or carbon buildup on the valves..

mxracer124 · Jan 10, 2010

crash said:
You either have sticky poppets on the injectors or carbon buildup on the valves..

Thanks for the help its my dads commuter rig to work. I just talked to him and he said he had ran it low on fuel before it started this....i've been told that can overheat the fuel pump? Low fuel preassure?

J_SIN · Jan 10, 2010

4.3's are picky with fuel pressure from what I've read but he also could have picked up some sediment from the bottom of the tank when he ran it low on fuel. If he can deal with the issue for another tank of fuel I would suggest putting a can of seafoam in the next tank to see if it will clean out the fuel system. if anything it wont hurt nothin and he wont have to spend much to try it.