I have a 2001 blazer 2 wheel drive that was in need of some work when i bought it. I put in a new upgraded injector spider and fuel regulator. it started and ran fine then the p0300 code came up. i checked for vacuum leaks (none to be found) i changed spark plugs and the code went away. then it came right back so i changed cap and rotor and spark plug wires. code went away and came right back. i checked battery and is good fuel pressure is good btw i put a new fuel filter when i installed the new injectors. Funny thing about the whole thing is the truck is running smooth without hesitation and not misfiring at all you could put a glass of water on the motor without spilling, that how smooth it runs. i drive and its like driving a new car. Shifts well and picks up smooth when you step on it but still reading a p0300 code....any suggestions??