I've got a little experience on lt1 engines, but this is totally stumping me and my buddies from the track. The problem started as a random misfire that would only occur for a few seconds after the car had been running for a long time. Now I will be cruising and the car will just randomly start misfiring, almost to the point that it dies. I had origanilly thought that it was a heat soak issue, so the ICM and Coil are new and i have done the cooling mod so that they are spaced 1/2 an inch from the head. The problem still existed, so now I have replaced the mass air sensor, manifold pressure sensor, and still no dice. Am I looking at an optispark biting the dust? The car is still driveable for the moment, as it has to be driven at lesat 30 minutes before the ignition goes what would now be described as 'hay-wire' Another idea that was thrown in was a fuel pump failure, but I dont see how it would still be going as this problem has existed and gotten worse over the last two months...any input is appreceated....

 

Have you checked for trouble codes? The opti would be a suspect.

 

If it misses bad enough in a row for a short time. Park it and start disconnecting each fuel injector at a time and see if you get a response from it. I just had a fuel injector clogged on mine that made my car miss very bad.

 

I just drove the car 40 minutes home from my girlfriends house in open loop and it diddnt hesitate one time. its been doing this for a few weeks like i said, about 2 weeks ago i had the intake manifold off to fix oil seepage off the back side of the intake from my cam swap last december. I checked the injectors, fuel pressure, and had a scan done and I have absolutely no trouble codes. Since its a weekend driver I think im going to start tearing it down and take the opti out and just replace it since it does have 130k on it anyway. Just to list everything if anyone else has something to add heres what have been ruled out and or replaced:

Coil
ICM
Mass Air Sensor
Manifold Absolute Pressure Sensor
Fuel Pressure Regulator and Pump checked, psi good at startup and warm/hot idle

again its an intermittent misfire, sometimes it runs strong without missing a beat then sometimes it just up and starts missing horribly.

 

A bad set of plugs/wires caused random misfires for me, you could try replacing those too.

 

anyone think that this could be a vaccum problem? i just discovered that my throttle body screws are less than finger tight, and from the oil/residue from the PCV system that had leaked down the front of the manifild i'd assume that the leak was pretty bad...

 

ttt

 

opti or fuel pump ,

same thing happened to me when my fuel pump went bad, id drive around for a while then it would start missing really bad and sound like it was running out of fuel

u can smack a fuel pressure guage on there and check the pressure, if its fine take it for a ride and c what the pressure does when it acts up , if thats fine then its another problem , prolly ignition

 

Well I changed all the plugs from splitfire platinums to autolite 106's and found that 2 of the boots on my new set of accel ectreme 9000 wires pretty much desentigrated. put in new wires, unfortuneately i havent had a chance to drive it since then..Im willing to bet that since i had t plugs arching and the gap on the split fires had opened up to .060-.065 that it had a big hand in my problem. Thanks for all the help guys!

 

I assume you force it into open loop??

 

Basic rule with checking these types of issues is you need 4 things.

Fuel
Air
Spark
Compression

by checking the fp under load with a guage and a compression test of each cyl will narrow it down to either a lack of air or spark.... you dont seem to have a blockage, so look at spark. IF you got rid of the 1st 2 possibilities.