I've been chasing a stumble for a about 4 months and cant figure it out. I put a cam and did some mild porting on the heads and ever since then it runs like crap. I've double checked everything I did and mechanicly, its done correct. Since it was my first time doing a cam swap alone, I labeled everything, vaccum lines, wiring harnesses, etc. I also replaced everything I took out, springs, lifters, opti, etc. I also had my PCM tuned by madz28.com. The problem is, the car stumbles under 2000 rpms and feels sluggish at all times. It is also running very lean. I checked the fuel pressure and with the key on, engine off, it only makes about 35 psi. With the car idling it makes 41 psi. I drove around with the guage taped to the windshield and it stayed at 41 psi, even when stumbling. The car ran perfect before the cam swap. The car has 160k miles. Should I replace the fuel pump and upgrade the injectors? Could that be the problem or maybe something else? Any advice is appreciated.

 

Mine does the same thing since cam and heads swap.. stumbling/surging.. what cam do you have? I have the cc306 I had madz28 do my tune for it, running really lean at idle 160blm's also. getting dynotuned on fri. hopefully that will clear up my problem. my fp is reading fine. new kirbin afpr walbro 255lph fuel pump. and autometer electric in dash fp guage... I don't lose any pressure. I will let you know if the dynotune works. that is about the only thing it can be now...

 

You indicate 41psi at idle. Is that with the vacuum compensation line disconnected from the FPR? What is your MAP (or conversely, what is your intake vacuum?) at idle?