I have a 2000 GMC 1500 Sierra with the 4.3L engine. Under a load such as entering a freeway, going up hills or even driving into a stiff wind, the engine starts to misfire. I have thrown a lot of money at this thing. Spider injection, distributor, plugs and wires, alternator, fuel filter more than once, throttle position sensor, computer. Engine code P0300 says Cylinder misfire detected random cylinders or P0304 cylinder 4. The catalytic converters were stolen and not replaced so those codes are always present.
Aany ideas will be greatly appreciated.
please provide mileage
Considering the age of the vehicle it's probably a good idea to do a compression test
Please search the forum, as this questions gets asked a lot.
Misfires are covered in the FAQ (main page)
Your first steps should be to measure fuel pressure, and check for vacuum leaks.
Intake gaskets frequently fail on the rear two cylinders.
https://carkiller.com/scottykilmer/qa/2002-s10-4-3l-hiccup-while-maintaining-speed/
