My 1990 c1500 withe the TBI 350 will start and run fine until it warms up then it seems to stutter when you get in the throttle and overall just runs rough. Seems to fall on its face when it shifts and will stall when put in gear. changed plugs and wires, coolant temp sensor.

 

How about cap & rotor and icm

 

Cap, rotor, and icm are all almost brand new. Haven’t taken them apart but it seems to be firing correctly.

 

Probably need to check out the fuel pressure system. Bad pump or regulator.

 

look at things that only happen after the car warms up, ie

oxygen sensors (if intermitten can cause crazy stumbling and not necessaryily show the code)

EGR

intake gasket leak (cold engine: use spray-9 around gasket, spray carb cleaner around gasket with engine running. any change in speed when gasket is sprayed is not allowed)

(if you have california emissoins on a carburetor, there are mechanical jigs and many tubes on the carb - see those are all in order. btw never spray spray cleaner on the outside of the carb where things move it will loosen plaque and re-harden inside the sleve - damaging the carb. only clean it the right way)

 

"start and run fine until it warms up"

"then it seems to stutter when you get in the throttle" (could be intake gasket, although that can cause need of rich condition on starting)

"and overall just runs rough"

"Seems to fall on its face when it shifts and will stall when put in gear" (cannot handle load conditions - possibly check transmisstion connector see if clean)

on almost all cars trucks, the fuel air ratio is controlled by your throttle plate. for carbuerator that means the fuel spray is constant for a given vacuum CFM inrush rate. (for injectors the mixture is determine by the MAF vacuum air sensor)

(from Chiltons). all problems are air, fuel, electricity

so you stumble only when hot. it can only stumble if short of fuel (rich/lean), vacuum is suddenly missing (gasket leak or egr wrong/leak), or electrical (when your wires get hot they stop working - but you said you replaced those)


"stalls when put in gear". YOU MEAN AFTER IT WARMS UP RIGHT? you don't have a transmission problem right? you said it runs fine until warm i assume that includes driving it.

HOW DOES IT PERFORM on the road, in this condition, if you go wide open throttle. does it die or suddenly have all it's power? (this might tell you if full vacuum advance full rich, being a cure, points to that intermediate advance and fuel trim are a problem)

exclude the easy things. bench test parts you can't exclude one by one.

never assume a bad battery or regulator can't cause problems diagnosing.

electrical: pull all fuses un-related to operation to insure there are no parasitic electrical issues. clean all grounds. really you often exclude this by checking for spark with some tester. and do deeper tests last if it checks good. although, knowing if spark advance is "way out" might be nice, probably leave that for later too.

 

I have a 95 g2500 acting the same way. Did you find the source of your problems?
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