Need some (any) of your brilliant opinions here......

'95 LT1 ZF 65k

6 months ago (perhaps 3,000 miles) I replaced the opti and a few sensors, cleared my codes, been running excellent and (mostly*) consistently since then. (*The occasional odd thing like suddenly starts running VERY bad in open loop one day....then it's fine for a week or ten ) (((Always been suspicious of my ECM.)))

About 6 weeks ago I carefully washed the engine. Carefully. 10 minutes after leaving the carwash, it stalled at a light. Tried to start it and as it turned over, it would mis-fire EXACTLY like the timing was way off, you know? Kept trying till I drained the battery (because I'm an ignorant optomist ). Towed it home. Only code was H50 (low voltage). Charged the battery overnight. (Classic Opti. "Let it dry out", I told myself.)

Next morning (dry & hot weather) same thing......no start, misfire. (no codes)

NEXT morning, starts right up and runs perfect.

Ran good till the other day. Again, pulling away from a stop light (hard).....engine just shut down. (btw...been dry as a bone here those few weeks....and I didn't wash the engine this time ) Exact same symptoms.

This time, I disconnected the battery and charged it (2Amp) overnight and tried it again (only because it seemed to work before). No go. Same problem (spins over, occasional burp (once per revolution), not even close to starting) No codes.

I had always thought "classic opti". But now I'm thinking perhaps my ECM is my problem? Surely my new cam hasn't broken (or cloyes chain, etc). I doubt it, but I added that question because it best describes the way it turns over, you understand?

I'm just too busy to work on it for the next week or so, just wanted to get some opinions and advice to think about before I start working on it.

Someone suggested the ECM grounds should be checked? Perhaps that's the first thing I should do, to eliminate that possibility?

Any thoughts would be greatly appreciated!

 

If something had broken in the cam or drivetrain, it would not run part time, it would not run at all.

As for the opti, people blame it for things like this, but for initial problems after the wash, I am betting the wires were simply wet.

Are you getting any codes? Can you get any codes? If you can't even get a C12 off the ECM, then there is a problem with the ECM.

Start there...

 

Thanks for your response Bogus,

Yes, I agree about the valvetrain. It's likely fine. I added that to best describe the no-start symptom.

Regarding the wires getting wet......I would agree, except the second time this happened (exact same symptoms), everything was bone dry.

I'm getting C12 every time. However, it's not run since I last cleared the codes, so it's not had time enough to create any new codes?

When I finally DO have the time to work on it.....I don't want to start with the opti, because I'm thinking it may in fact be fine. (hoping, rather)

Oh, I forgot to mention that I also replaced the ICM in hopes that it would prove to be the problem. No luck.

 

Have you worked on it yet? Im real curious because my 93 has been
sitting in the garage for 3 months with a similar condition. I even exchanged
my new MSD Opti thinking it might have been defective, But no luck Let me
know what You find!

Check out this thread if ya have the time!
http://forums.corvetteforum.com/show....php?t=1466770

 

Had a '91 Regal with symptoms like yours. Totally different ignition, of course, but read on. Finally found a factory service manual and tried to read codes (none) when the car was 'operational'. Then during a no-start condition, noticed that the 'service engine' light didn't come on when the code reader was installed with the key on.
Manual said to check ECM ground (because of no 'service engine' light during code reading) and if it was OK, ECM was bad. Ground was good.
New ECM (rebuilt $100) and car ran fine.
Your '95 Corvette has OBD I so likely has the same diagnostic possibility (haven't found it in the FSM). That is the 'service engine' light should come on during code reading to indicate communication with the ECM??? If not, bad ground or ECM.
Long shot but easy to check out.
Hope this helps

 

The c12 should mean the ECM is communicating and there are no codes.
That should also mean the opti is fine, but a loose coil wire would also do everything you describe and throw no codes. You said new Ign Module? You did use the heat transfer goo? Still possibly a bad module, but I believe that should throw a code. Low voltage from the coil is another possbility. I would check for spark at the plugs first, then back track to the above. If electricals are good, then fuel pressure check would be the logical next check. Hope it is something simple and cheap.

 

Thanks guys for all the advice!

Unfortunately, I've been too busy with work to look at it. (Mostly out of town projects). This next week or two will be better.....and I'll let you all know what I find.

Thanks SO much for the pointers!

 

One other thing to check:

The coil!!! My 92 had some classic "opti" symptoms when it died on me one day. A friend with a 92 suggested I try changing the coil before I blamed it on the opti. I was getting NO codes, once I replaced the coil the car started right up and has been running great for a couple of months now including a 1900 mile trip!

 

not only the coil, check the harness TO the coil and ICM... they are known to wear out and cause all sorts of problems.

 

You're right Bogus. About 8 months ago I replaced the connectors @ the coil (ebay new/cheap like borsch...dealer discontinued) as well as the opti connector (dealer new/HUGE$ ). Both items were replaced due to some corrosion/breakage. Sort of a preventitive/detailing measure. Recently, I traced all my ign. primary wiring looking for damage. It's all good. Except now I need to re-tape & re-wrap it all.

Jaa, You may be right about the coil. Stupid me, I never pulled the coil wire to check for spark! That'll be the first thing I check, for sure.

 

The reason it never occurred to me to check for secondary spark was the fact that every revolution it would try to fire up. Consistently. Then I searched this forum and found that the ICM can cause this problem, so I eagerly threw a new one at it (properly, w/the heat grease, etc) because I was wishing for a miracle cure. I also don't mind a bunch of new service items throughout as I want to keep the thing.

I'm thinking I'd better get a new opti. Just in case. I hear the opti's will last forever (on a shelf).