car stumbling after 3k rpm

[94LT1Z28]

the opticrap switch is complete, i have the car back in time and it is still runnning like !@#$. I cannot figure this one out. I tried another computer, plugs, wires, coil, fuel filter, knock sensor, air pump and harness, icm, and cap and rotor. Still having the same damn issue. This is going to drive me nuts before it is over with, lol. Any ideas or advice? The car dies if you hit the throttle hard and it stumbles if you rev it slowly above 3 grand. I am trully stumped..... Any advice would be greatly appreciated. As always thanks in advance....

[lt1maro]

fuel pump or fuel system maybe? just a suggestion.

[94LT1Z28]

I checked that too. You forget to mention things when you are so frustrated you want to blow the car up, lol. Thanks for the input though.

[Joe 1320]

It would help us if you list the specifics like year, engine, etc. for better diagnostics.

[94LT1Z28]

Lol, my apolgies. I have a 94 lt1 z-28. I have even run the codes on the car, and nothing comes up. I am stumped. I have been working on this thing for over a week now.

Current Mods: Dart aluminum heads, 4.10 gear, lingenfelter aluminum driveshaft and flywheel, msd 6al box, custom programming, and 52mm throttle body

[Joe 1320]

Running a scan tool would be helpful. The ability to read sensors in real time will tell you what the computer sees. Couple of points to remember....... The cap and rotor portion is only one part of the opti that can fail. I've seen brand new units go bad just after startup. I know you checked fuel pressure, did you check volume as well? How many miles on the injectors? If one or two were not up to snuff, the car may nose over. Ditto for fuel volume (pump). Also have the coil driver module checked as well as all harness connections. I have seen a fualty harness connector at the coil module give drivability problems without throwing any codes. Exhaust leaks prior to the 02 sensors have been known to throw the mixture off as well. Could be more than one problem that adds up. Even the EGR, if faulty can cause surges.

[94LT1Z28]

Thanks for the info. I will give it all a shot. This is the third new optispark. I wanted to rule out a bad opti spark like you said, lol.

[94LT1Z28]

I have been through everything but the fuel pressure again now. Does anyone happen to know what fuel pressure should be at idle? WHat should it be under load? I am starting to lean towards a fuel delivery problem being that the car idles fine, but break up under any type of acceleration. This I was originally told was caused by the optispark, which does not seem to be the case now. Any new ideas? All help is greatly appreciated, especiallt since there are no performance shops here that I trust. Thanks again. Also, how can I test the EGR and fuel volume?

[Joe 1320]

Fuel pressure should be approximately 44 psi at idle. Volume is checked by using the bypass line of a pressure/volume gauge. I've seen pumps check fine initially but the instant the engine demands more fuel, the pump can't supply ample fuel so the motor loses power and pressure drops. You might not know it unless you can run a gauge that is taped to the windshield wipers so that it can be read from in the car while the motor is under load. Bottom line is that fuel pressure and volume should not drop as you go WOT.

[94LT1Z28]

what do you know, it turned out to be the fuel pump. 7-9 psi at key on position. lol, thanks for all the input.