1992 LT1, 43000 miles, I have installed , new distributer, new wires, new plugs, new fuel pump with strainer, new coil and I still start breaking down above 4000 rpm , popping and running on 7 cylinders, any thoughts, i am running out of ideas to solve this problem. Thanks Alan

Do A compression check

1992 LT1, 43000 miles, I have installed , new distributer, new wires, new plugs, new fuel pump with strainer, new coil and I still start breaking down above 4000 rpm , popping and running on 7 cylinders, any thoughts, i am running out of ideas to solve this problem. Thanks Alan


Rather than throw more parts at it, you need to find out what's wrong first. You need to check your fuel pressure, but low fuel pressure won't cause it to start missing at high rpm. It'll just lose power. Only an ignition problem will cause misfiring. By any chance do you have your spark plug wires tied together with nylon ties? If you do, you shouldn't. The wires need to be seperated, and wires #5 and #7 spaced far apart. As #5 and #7 fire one right after the other, the spark can flash over to the other wire. So make darned sure those 2 wires are far apart. It sounds to me like you have a leak in your ignition system somewhere. Try running your engine in a totally dark garage late at night, and look for any signs of spark leakage. If you have an automatic transmission, put it in gear and hold your foot on the brake while giving it a lot of throttle. If you do have spark leakage, it'll show up.

Rather than throw more parts at it, you need to find out what's wrong first. You need to check your fuel pressure, but low fuel pressure won't cause it to start missing at high rpm. It'll just lose power. Only an ignition problem will cause misfiring. By any chance do you have your spark plug wires tied together with nylon ties? If you do, you shouldn't. The wires need to be seperated, and wires #5 and #7 spaced far apart. As #5 and #7 fire one right after the other, the spark can flash over to the other wire. So make darned sure those 2 wires are far apart. It sounds to me like you have a leak in your ignition system somewhere. Try running your engine in a totally dark garage late at night, and look for any signs of spark leakage. If you have an automatic transmission, put it in gear and hold your foot on the brake while giving it a lot of throttle. If you do have spark leakage, it'll show up.
and if that doesnt yield any result, the next place i would look is valve train a badly worn cam lobe or burnt valve or collapsed lifter

It's possible you have a broken valve spring causing your high rpm misfiring. Can you hear any unusual noise coming from either side of your engine? Any kind of ticking noise?

good luck my friend.:thumbsup:

So did you find out what is happening? If you did, let us know what it was.

keep it below 4 K

This is just a thought, I believe the LT1 computer has a built in rev limiter at around 4600 or so RPM. It is not exact. Not sure how it gets the input. Maybe somebody here with more knowledge can shed some light.

Repaced the ecm and fuel filter, same problems,moved wires on 5&7 STILL NOTHING, engine is quiet, no ticking or noise from heads, no noise from engine. i put a new AC Delco dist. have you ever heard of on of those being bad?

You changed out the optispark?????? How much did that cost you?

Repaced the ecm and fuel filter, same problems,moved wires on 5&7 STILL NOTHING, engine is quiet, no ticking or noise from heads, no noise from engine. i put a new AC Delco dist. have you ever heard of on of those being bad?


Did you happen to replace your distributor to correct the misfiring problem? Did the new distributor come with a new cap on it, or did you use your old cap over again? If you used the old cap over again, it may have "carbon tracking" between the top spark plug wire terminals. Or it may have a worn out (or missing) carbon button in the middle. Take a good look at the inside of the cap and look for evidence of carbon tracking. Carbon tracking will look like a wandering pencil line that goes between two terminals, or from a terminal down the side (to ground).

Did you happen to replace your distributor to correct the misfiring problem? Did the new distributor come with a new cap on it, or did you use your old cap over again? If you used the old cap over again, it may have "carbon tracking" between the top spark plug wire terminals. Or it may have a worn out (or missing) carbon button in the middle. Take a good look at the inside of the cap and look for evidence of carbon tracking. Carbon tracking will look like a wandering pencil line that goes between two terminals, or from a terminal down the side (to ground).

He says he has a 92, which means an LT1 with an optispark. A little different critter.

REPLACE WITH A WHOLE NEW DIST ASSEMBLY,CAP AND ALL. IT WAS A AC DELCO THE ROTOR AND COVER WERE ALREADY INSTALLED. SEALED UNIT I THINK IS WHAT THEY CALLED IT. COULD IT BE A CLOGGED INJECTOR? iF I ACCELERATE SLOWLY UP TO 5500 IT DOES NOT MISS, BUT AS SOON AS YOU NAIL IT AT 4000 IT GOES TO HELL.

New optspark cost 485.00

Try this quick easy check. Go outside in the dark (darker the better) and start it up. Look very carefully for any sparking from shorting out plug wires and look closely at the coil to opti wire. After it warms up a bit drip a couple of drops on each exhaust manifold to block port. If you have a 'dead' cylinder the water won't boil off. Did you check fuel pressure after changing the filter?

Try this quick easy check. Go outside in the dark (darker the better) and start it up. Look very carefully for any sparking from shorting out plug wires and look closely at the coil to opti wire. After it warms up a bit drip a couple of drops on each exhaust manifold to block port. If you have a 'dead' cylinder the water won't boil off. Did you check fuel pressure after changing the filter?


That's what I suggested in the very beginning. Look at the engine when it's totally dark outside. It sounds like he's losing his spark somewhere; flashing to ground.