I've just about had enough of this car. I think I've worked on it so much that I can't think objectively anymore. I need a little advice from some people that don't have my level of frustration.

Here's the problem. I have a spitting (random sounding) miss at low-load part throttle. from about 1200-2500 rpm with no load or very low load the engine shoots ducks. As soon as you put a little load on it it straightens right out. If you hammer the throttle,the car flies. I've had this problem from the day I started this 383. Sometimes it's better, sometimes it's worse, but it's always there. It's almost impossible to run it steady at highway speeds because when I level it off, it starts missing. It seems to get worse as it warms up, but it's there at every temp. As an added bonus, now it's cutting out, loading up and trying to die-but this is something that has only happened since I changed the heads and intake last week, so I think it's a different problem. (I was sucking oil out of the intake with the last head and intake combo, so I was hoping that was the source of the miss as well-no such luck.)

Here's a list of things I've done that have NOT changed the problem.
1. Delteq Ignition, 2. New plugs, 3. Different chips from different programmers, 4. Different injectors, 5. New heads and intakes, 6. Programmable MAP sensor (which I've since removed), 7. I disconnected the O2 sensors-didn't change anything the problem is there in open and closed loop, 8. Removed the PCV valve, 9. Raised and lowered the fuel pressure-no change either way. I'm sure there's more, but I can't think of it right now.

The engine is a 92 LT1 383 with 9:1 compression. P1SC Procharger. Ported LT4 top end. Comp cam blower cam .510 lift, 224/236 @.050, 114 lobe seperation. 93 Camaro PCM, harness, and 2BAR MAP program (by Alvin).42# SVO injectors, adjustable fuel injectors. Delteq ignition. 94 model Opti. MSD wires. Long tube headers, dual 2 1/2 inch exhaust with X-pipe and 2 chambered Flowmasters. There are no trouble codes stored and all scan tool data appears normal.

Any help you can give me or ideas of things to check would be greatly appreciated. I teach this stuff for a living and did it for a living for a long time before that, but I'll be the first to admit I don't know everything and occasionally get my *** kicked by a vehicle (thankfully, not often).

Thanks in advance.
JIM

 

At least for me, there're almost too many variables. I'll assume you've had this on an engine analyzer to see some things, and that all ignition parts have been tested throughout the rpm range. With all the engine work, you mention multiple chip programs but has anyone designed one with the car up on/after being on the dyno?

 

Thanks for the response....

I've had the factory ignition-with and without a MSD 6AL, and a Delteq. The miss was there with all of them, I've changed plugs several times and that never helped, either.

I have not had a dyno tune done. I know I really, really need to have a dyno tune done, but it is difficult to do where I am. I hope that is the culprit, but with tunes from three experienced different tuners, I have my doubts that all of them would miss in exactly the same way.

I realize there's alot of variables given the wierd combination I have, I'm just hoping that this problem will ring a bell with somebody here.

 

 

Just an idea......but how about swapping out the ECM with a known good one?

 

I will toss in a couple of thoughts...

1) Check all the grounds around the battery. They have a tendency to corrode.

2) I agree, test the ECM with a known good one.

3) Check the harness to the opti. If it's corroded, all sorts of weird **** will occur.

 

I'll check the grounds. I know it doesn't take too much corrosion to be a big problem. I've checked them in the past, but it's been a long time.

I haven't checked the harness to the opti, I'll pull that out as well. I put a scope on the signal wires out of the opti a while back, but it wouldn't hurt to do it again.

I'll see if I can run down a known good ECM. With it only fitting one year of Corvette and one year of Camaro, it may be a tall order. I've got friends in the salvage yard business, maybe I can call in a favor.

Thanks for the help, keep the suggestions coming.

 

Have you checked all the vaccum lines?

 

I had a carb'd 327 that had your symptoms - including sucking oil. Took weeks to discover that it was a leaky PCV valve -- but you already removed that??? I found the bad PCV valve by plugging it up.
Is it possible that the EGR or IAC (or other vacuum site) is leaking very slightly and becomes noticeable only at part throttle? Or perhaps a 'boogered' throttle body shaft/housing that leak at only one angle?
There was a thread a couple of weeks ago that described seeking vacuum leaks with a very low flow of propane from an unlit torch. When the propane flowed into the leak, the mix would richen and the idle would smooth out. I haven't had the occasion to try this technique but it should work in a very well ventilated area.
Good luck and please post when you find the solution.