1990 Chevy pu with a 4.3 runs great cold then warms up and spits and sputters Any Ideas?
I would have the O2 sensor or sensors checked. They are usually what sends the signal to the PCM on how to set the fuel codes as far as rich and lean. If they are sending a good signal at cold, and telling the computer to richen the mixture and as the engine warms their signals should change to tell the fuel delivery table to begin to cut out fuel and go to a more normal mix. Yours may not be getting the warm code sent to the PCM and your fuel trims are staying on the rich side. Running too rich will foul up the O2 sensors and could ruin your catalytic convertors as well. Find the exhaust manifold and you will see the O2 sensors. They can be removed and take them to a testing place maybe Autozone and try to see if they are within specs.