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.

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

 

did you put new lifters in? know it sound like strange question, but this did the trick for me with very similar problems...

rhodes v-max.

i am still not sure whether it was the lifters or a vacuum leak fixed by reinstalling the intake. all i know is the exact same symptoms went away...

however, i am not blown. do blown engines have the same issues with vacuum?

 

sounds like a vacum leak

 

I also had a similar problem when I put my new engine in about a year ago, I was sucking air / oil into the number one cylinder, apparently I didnt have the intake installed "straight"...

I found this problem by hooking up my Autotap program and looked at the cylinder that was causing the most misfires and fouling plugs like crazy. Since you have your O2's disconnected it is hard to say what the ECM is trying to do unless the O2's were programmed out of the system. I was also experiencing the Cat's glowing, I found that the shorty header flanges were leaking exhaust and was causing the car to go very rich as the O2's were sensing the fresh air it was sucking in. .

I would "forget" everything.... go back and get yourself a baseline and "start-over" . I had to do the very same thing. It really paid off.

I broke the engine in without the supercharger, after I had things ruinning smooth, then i added the supercharger and at least had a baseline to start from.

I hope this helps... sometimes it is best to step away and then go back when you have a rested and fresh mind. I know it is VERY had to do that...

Hope this helps some... Good luck and "remain calm" .. it will come together.

Mo

 

Thanks guys.

The lifter thing is something I have not thought about, if I had one intermittently not bleeding down I guess it could cause the same problem. At this point, I can't rule it out.

When I changed plugs yesterday, #1 did seem like it had a little oil on it. I wonder if there could be some reason the intake could be not going on right. On the old heads and intake setup, #1 seemed like it was sucking in the most oil. But I thought changing heads and intake would eliminate the possibility of it happeneing again. Wonder if thicker or different manufacturer intake gaskets would help.

I'll put the smoke machine on it and look for vacuum leaks. Couldn't hurt, anyhow. I've done it in the past, but haven't done it in a while.

Thanks again for the ideas.

 

Have you changed the optispark? I run an LTCC and assume the Delteq high and low res signals are driven by the optispark, as well. Make sure your opti vacuum is not coming from someplace that can go boost (i.e., intake) as that can cause moisture to get blown into it (check valves won't hold under boost).
Good luck!
CT

 

You don't mention what heads and intake you are running. I was putting on a LT4 intake with a set of AFR 210 heads.

I originally went with Felpro gaskets, I went with the OEM LT4 intake gaskets, they seemed to resolve the problem.

I was fouling the number one plug literally closed!

Hope this helps

Mo

 

I'm running ported LT4 heads and intake I bought here on the forum. I had them checked over and freshened up before I put them on. Right now I have GM intake gaskets on there.

I have a borescope at work, I think I'll pull the intercooler and throttle body and look at the intake runners to see if any of them are oiled up. With no PCV there shouldn't be any oil in the runners.

I don't know what I'll do if I find oil....

 

If you are still sucking oil, i would check to see that the mating surfaces between the intake and the heads are aligned properly.

Merry Christmas to you...

Mo