cubby-5056

Hello all. Anyone with lots of lt1 experience?
Brief description. The last two seasons my lt1 has had an intermittent misfiring or lack of power. No issues until I've been hopping around for at least 20 min. Sometimes more then it will just start loosing power. Up till that point it is all good runs strong lots of power and no hesitation.
Last year I changed the opti, ign coil, ign module. Iac, Tps, plugs and wires are about 5000 km
Engine has a cam , lt4 intake , headers, no cat, magna flo exhaust

The engine is from a 95 Camaro and the PCM has been programmed and is in my 1991 camaro

Fuel pressure was good and consistent even through misfiring 43 psi

cubby-5056

Oh and vacuum through the opti spark seems good. The car has 4:10s and I tend to drive it at high rpm quite a bit. Highway speeds are consistently at 3000 or maybe more rpm

Thirim

I had almost the same issue. Eventually it was doing it often enough that I could make it happen in the driveway. I threw an ICM (Ignition control module) at it and it's been happy ever since. I think I changed the coil at the same time just because.

Thirim

I also had a bad fuel pump about a year later. I suspected the pump but it was always testing ok. It finally died and wouldn't run. Dropping the tank is loads of fun.

tglennon11

iTrader: (2)

when you did the ICM did you add heat sink thermal compound? I have heard/read issues of the ICM getting hot and that causes some of the missing. I have the same issue, and am planning on adding the compound as soon as the cover comes off in a few weeks.

If you find something else the cause, please post it up so I can look into that as well

cubby-5056

Yes I read that about the heat compound also. I did put some on there. I don't know what's up with this thing. It is very frustrating. I have some incomplete wiring so I'm going to pull all my wiring and redo it.

I'll post what it was when /if I find it


Fuel pressure was good and consistent through out. Even during the miss. My mechanic bud did the fuel pump test and it checked out

cubby-5056

Will not having the VSS connected affect anything? The PCM won't know the car is moving but I can't see it affecting spark but who knows.....hopefully someone here

Thirim

not sure on the VSS but I doubt it. The PCM needs the MAP/MAF/TPS though. Speed really has little if anything to do with the PCM, think about it, you're doing 50mph on a flat road or straight up a slope... If the car applied the same rules to both then the car would run good for one and fall flat on its face for the other. I know the PCM sends the speed to the speedo and the cruise at a different configuration than is received. 2000ppm for the speedo and 4000ppm for the cruise I believe. The VSS signal is in pulses per driveshaft revolution.

cubby-5056

i thought maybe it might adjust timing or something if it knows it is moving versus idling on the driveway due to the fact the vss goes through the pcm. It's such a gremlin. Reaching for anything now lol

55ChevyMan

Just wonder if it was fix what was the problem ? mine I driven under 30 mile since engine swap and it turn but won't start change plugs and wires and a Ignition module fuel pressure is 43 PSI if i put either it try to start thanks

Thirim

Do you have spark?