P0300, Checked Everything And Need Help!

[Gregs]

Hey guys this is about my truck in signature.

 

As I was leaving a parking lot the truck started sounding weird and the check engine light comes on. It started shuddering and the check engine light is flashing so i know that its misfiring. It was chugging so hard i barely made it up to 20 mph so i pulled to the side of the road. Everything looked ok so i started it up again and drive home without any problems. Scanned it and all it has is p0300. Watching misfires at idle I have about 4 per cylinder that go away if I make the engine idle up. I'm thinking the misfires at idle are because of my cam. it doesn't have cats so its not like that could be the problem.

 

here are the results from the tests i have done:

 

-Tested fuel pressure at key on, idle, and driving down the road and it was all good

-Tested FPR on cold and hot engine with vacuum gauge. Also not fuel is leaking past the seal

-Ohmed out the injectors and they are all good

-Vacuum tested manifold for leaks and none were found, intake gaskets were done last year.

-used my Efilive to check for a case error and none was found

-Did coolant pressure test and it was good

-did coolant chemical block test and it was good

-pulled plugs and wires (both have less than 1000 miles on them) they are like new, plugs look great and all the wires ohmed out really good

-did compression test and all cylinders were within spec

-no exhaust leaks or restrictions

 

i did get a freeze frame but from it it looks like ltft and stft were good.

 

I should mention that i cleared the code and it came back on however i haven't felt it misfire since the first time that the light came on. so i guess its having a misfire that's not really noticeable to me but the computer is picking it up. Power is like normal right now.

 

i'm running the comp cam in the sig with comp hardened rods and ls9 springs, so i don't think its a valve train problem.

 

I really need help with this one, i already stumped two of my mechanic friends

DTC_0239.txt

DTC_0239.txt

DTC_0239.txt

DTC_0239.txt

[Jsdirt]

Only things I can think of are cam and/or crank position sensors. As long as the injectors are ok ...

[Stevens03]

MAF sensor, is it stock and if so, when was it last cleaned?

 

Alot of P0300 codes I've seen come from a dirty MAF sensor or non-stock sensor. Especially if your running a K&N filter.