I need someone to tell me where I go next. I have a 96 sonoma with a 2.2 5 speed that is setting a p0300 code. It is misfireing when the truck starts to load the engine on a pull up hills or when you step on the gas and load the motor. Have already replaced every sensor on the motor except the egr valve but have had it off and cleaned and checked it. Have put a computer on it, a new fuel pressure regulator, all new vacume lines,had valve springs out and checked them, new plugs and wires and 2 new injectors. Truck runs fine on the road till you hit a hill and then looses speed and when you give it gas it starts dropping cylinders. Also will fire back through the intake sometimes. I have noticed it seems to run better when you first start it up and it's cold but still does it if you go to WOT. Have mechaniced for years but have never ran into anything like this before. Anybody had this problem? About to run out of time and money if you know what I mean. HELP!!!

Replace the ignition coil. It's more difficult to shoot a spark through alot of air/fuel mix than a little.

Replace the ignition coil. It's more difficult to shoot a spark through alot of air/fuel mix than a little.

It actually acts more like a timing advance problem than anything else, even thought I know it is controlled by the ecm. Truck runs great till it starts to pull on a hill or if you go to pass then if you ease into the gas it seems to be ok for a bit then it starts missing but you can let off the gas and it smooths out. I have already replaced the coils and the module. Didn't change any. Have litterly changed everything but the fuel pump, cat converter and the egr valve but did take the egr off and clean and check it and it seemed good. Still acts like the timing to me. Truck starts on a quarter turn and idles smooth. Have mechaniced for about 40 years but not really up on some of the newer electronics. What tells the ecm to advance and retard the timing? Could it possibly be a coolant sensor somewhere?