raptere

Hey all,

So my 1991 Camaro z28 TPI L98 350 is causing me some grief. It is not my primary car so it doesn't get driven that often. I like to drive it on nice days but because my commute to work is 26 miles I don't want to get stranded, I have to trust the car and currently I don't. Unfortunately it has to sit outside because I have nowhere else to put it. It is under a car cover for the winter months. I also did most of the mods on the car back in high school 9 to 11 years ago.

I went to pull it out the beginning of this summer and it was having a lot of trouble starting. It randomly sometimes just wouldn't start, other times it was fine. I was able to attribute that to something in the distributor, while I could have done more testing to determine the exact problematic part, the distributor appeared old and weathered so I instead replaced the whole distributor with one from D.U.I which appears to have solved the hard starting problem.

Now the on going problem, when I rev the engine stationary in park, it will be fine for a few revs then randomly around 2500 rpm it will just die, no spuddering, no trying to restart, no loss of power, just dies. It has done this to me while driving too.

Relevant vehicle specs:
-SLP 1 3/4 shorty headers - Magnaflow catback - dual cats
-Cane Cams Hi-6 ignition box with LX91 Coil
-Speed Density (no MAF)
-Holly Stealth ram intake and dual 58mm Throttle Body
-AIR system and EGR deleted.
-700R4 Auto Trans
-Initial timing (brown wire disconnected) set to 8* BTDC
-Running 93 octane

What I know:
-Complete new Distributor (D.U.I.)
-Relatively new battery, good voltage and cranking
-When engine dies it looses spark (I hooked a timing light up to the #1 plug wire and the second it dies, before the engine has stopped rotating the spark abruptly stops)
-I have tested all of my injectors cold at least and while they are not quite in spec they are all within about .8 ohms of each other which I think is enough to rule them out (if not let me know)
-Fuel pressure primes to about 47 PSI then drops down to about 40 while then engine is running and revving, have and adjustable regulator so I need to adjust it up to 43.5 PSI (Chevy stock spec?)
-I have cleaned my throttle body and all passages and IAC valve (haven't tested the IAC though)
-Have tested my TPS and while it is just a hair out of idle adjustment, it has a smooth progressive voltage sweep though its movement, so I wouldn't think that is the issue either.
-As soon as the engine dies, again before it even stops spinning, I hear the fuel pump prime for 3-4 sec, the same as it does when you first turn the ignition on.
-In dash tach works fine and external autoguage? tach works fine but recently has been loosing signal below about 1000 rpm and jumps up to my shift light RPM set point, which it should do only if the ignition is on but the engine ISN'T running, not sure if that suggests anything
-Strangely never shows any codes???

At this point I feel like I am really close to a solution, but I can't quite make sense of the facts and tests I have performed. I swore I had it narrowed down to a bad injector (hadn't tested their resistance hot) until I tested with the timing light last night and found I was loosing spark at the moment the engine looses power. Based on this thread, my issues looks very similar to his in his videos: https://www.thirdgen.org/forums/tech...305-idles.html

Sorry this post got so long, but please try to help me out!

Thanks,
Eli

raptere

No responses yet?

If this was your car what would you test/inspect next to try to find the solution? I really want to get the car running tip top before the winter shows up...

8Mike9

I'd have the ICM tested, and also disconnect the aftermarket tach..eliminate the easy things first.

raptere

By replacing the distributor I installed a brand new ICM, I do need to check the connections on the ECM though. It is above the passenger side foot well right?

You think the aftermarket tach could affect something. I mentioned that because I think it may be used as a symptom of the problem. Or did you mean try dis connecting the aftermarket ignition system all together. Once I get my old coil from my parents house, I will try that.

8Mike9

Yes, I mean disconnect it.

It might be the cause, or as you say a symptom, I believe the output of the ICM is what controls the factory tach and connects at the coil where the tach drive is at.

raptere

Hey all, figured I should update everyone on my situation.

I ended up replacing the distributor suspecting it was the ICM. After taking off the cap and seeing the state of the cap, rotor, and how rusty the rest of the distributor was I decided to replace the hole thing. That actual resolved most of the problems. I readjusted the timing, and it was running pretty well. I cant honestly remember what the problem was at that point, if it was still dying on me, or if the tach was still acting goofy, but after retracing all my wiring, I realized I had been referencing the wrong model of ignition box, reading the correct one, I realized I had a wire hooked to a switched 12v source that was supposed to just be taped off. Did that and all the problems went away.

The engine ran much smoother, but still not perfect, i then took out my spark plugs to check them and found they were completely spent. Electrode was so warn that the effective gap was something like .083". I also realized the shop I had replace them last time used the wrong ones and the threaded section was about 1/4" longer than it was supposed to. This also made getting the old ones out a bear! So far I have been able to replace 4 of them. I ordered one of the SLP cut off spark plug sockets and hope to finish the rest of the plugs in the next week or two.