I purchased a 97 Z. and it does not run well. It has a lingenfelter intake or throttle body on it and idle rough. It appears engine has bee out at one time. I don't know anything else about it. It idles rough and has little power. Runs alittle better at higher rpm. The exhaust manifolds look white.(maybe to lean) It runs on all 8 cylinders with no dead miss. It has about 38-40 psi fuel pressure and has I believe a 335 and 336 code form a snap on scanner...ckp sensor circuit. The engine sounds good mechanically but runns poorly...any help?

 

The codes are for a faulty CKP sensor. That sensor is only used for misfire detection, so its not the cause of low power. A benefit of repairing the CKP snesor is its ability to track misfires and allow the PCM to keep arecord of misfires byt individual cylinder count. That can sometimes help you identify the cause of a problem.

How did you test the fuel pressure - with or without the vacuum compensation line on the fuel pressure regulator. With the vacuum line off, you want 41-47psi. When you reconnect the vacuum line, the prssure should drop proportional to intake manifold vacuum, about 8psi drop on a stock cam. At WOT/max load/high rpm the pressure should hold within 2psi of the "no vacuum" reading you got at idle.

You need to determine what aftermarket components are on the engine. by "Lingenfelter intake" are you referring to the inlet air dfilter/ducting, or are you refering to the intake manifold? LPE sold a "Super Ram" intake for the LT1.... no way anyone could not recognize it compared to stock. Why do you believe you have an LPE throttle body?

Rough idle can be caused by a large number of problems... might want to check the EGR valve for leakage. What did the scanner show you for intake manifold pressure (MAP)? That might help you track a vacuum leak.

Rough idle could be dirty/leaking injectors..... lots of possibilities.

 

Fuel pressure was checked w/ vac. connected. The injectors and throttle body and intake as well as the rest of engine look almost new. The trottle bodt has Lengenfelter performance stamped in it and the rest of the intake has some type of marking on it I'll look at the exact marking and post it. Does this sould like a optispark problem?