I have a 02 GMC Savana 3500 350 cid vortex. For the past year it has been throwing a P0300 code. Several garages have tried to track it down with no success. I eventually put a piece of black tape over the light. This week we put a new GM 350 crate motor replacement in the van. I also replaced the plugs, wires, cap, rotor, and distributor. I put the intake back on with new gaskets and fired it up. All went well and the engine fired right up with no leaks, strange noises or fault codes.(at first) After warming it up and checking everything out, we took it for a spin and all was great until the dreaded P0300 code came back. I cleared the code and refired it. At idle it does not throw a code, only at run speed. Also, there are no symptoms such as missing or stumbling. This is the same problem I had with the original motor. It runs and feels great except for the flashing trouble code. I am at a loss. I had hoped that this problem would have been solved with the new motor. Well I was wrong. I am thinking a new crank sensor or MAP sensor. I hate throwing expensive parts at it to try to solve this nagging problem. Any ideas would be greatly appreciated. Thanks Ron .
PS. I also had the injectors checked for flow with the old engine to rule out clogged spider legs in the injector system and all was good.