[88K2500]

Originally Posted by misfits

I have a 2wd 1990 chevy 1/2 ton with a 305. I replaced the gas tank, sending unit and fuel pump and starting having problems with the truck running poorly. It stumbles and misfires. On light acceleration it runs like crap. But on heavy acceleration it sounds/runs fine.
So i replaced the fuel filter, cap, rotor, plugs and wires and one of the plugs had the electrode basically melted off. After that it ran fine for about 2 days now it runs like crap again.
The engine light isn't on but during a 15 min drive the light came on once or twice around 10 min into the drive then went off again. It did that 2 different times.
I scanned for codes and I got a 13 and a 42. I have a code 42 a while back and re connected the timing connector and cleared the light but apparently its still storing a code 42.
Is an oxygen sensor going to affect how the engine runs?

If you replaced all those parts and still have a misfire, you should do a compression check on all cylinders. Maybe you burnt a valve. Who knows. The compression check will tell you where the miss fire is. If the compression checks out good on all cylinders, I would start looking at the dizzy again.