Hello,
I've spent a lot of time on this site and am sad to say I need help. 1994 z28 auto with 92k. With slight throttle it accelerates smoothly through the gears. With moderate throttle, it craps out. It feels like to much air or to much fuel. New Walbro 255 fuel pump, fuel filter, TPS, ACdelco platinum plugs, fuel regulator and LT4 knock module. Removed CAT, cleaned MAF, MAP, IAC and throttle body (only thru the butterflies) No SES light, Datamaster program shows no trouble codes. Same problem on both open and closed loops. Spark retard and knock counts seem high to me and it is running rich when it is bogging. 02s seem to be firing properly. No tuning to my knowledge. The motor has a chirp when warm that follows rpms. I can't locate the source. I'm going nuts! and help would be greatly appreciated.

 

You may want to check the fuel pressure with a gouge while the engine is under load. If the plug wires are still the original, it would be a good idea to change them. A bad opti can also cause the engine to run poorly under load.
As for the chirp, my old 94 was chirping away annoying the heck out of me. After a lot of probing with a hose in my ear, I found out the noise was coming from inside the engine. It turned out to be the roller on one of the lifters stopped turning. Replaced lifter and cam and no more noise. But before opening things up, take the serp belt off & see how things sound, as the noise could be coming from one of the accessories, idler pulley, belt tensioner, etc..

 

I just took a drive today with the fuel pressure gauge taped to the windshield. Idles at 40lbs and goes up a couple of lbs under load. Pressure held for 20 min. so I'm thinking no leaks. A friend brought over his stethoscope and I clearly heard the chirping coming from the right side on the second valve cover bolt. Could the chirping be causing the knock sensor to go nuts retarding the heck out of spark? Although I thought in open loop the knock sensor isn't being used?
Any recommendations on plug wires?

Thanks for the quick response and advice,

Al

 

Do a tuneup it sounds like you need cap rotor and wires and that it's not sparking right maybe your timing is too advanced seems like a tuning or timing issue

 

Thanks for all the advise. I turns out it was a flat spot on a lifter. I replaced all the lifters on the passenger side, did valve adjustments and it runs great !! what a nightmare.

Thanks, Al

 

Love happy endings!!!

 

That is what happened to my car. Your lifter got a flat spot because it stopped turning and most likely chewed up the cam lobe. If you didn't replace the cam, the chewed up lobe is going to mess up your new lifter.

 

Perfect excuse to upgrade your cam