OPTISPARK FAILURE!

I have a 94 RMW 130K and have not posted here in quite some time. I had to replace the Optispark (not original)
because the plug port on the top had become compromised due to airborne oil residue getting down in there
after the plastic head of the plug had broken and it wasn't sealing well.

After a lot of research I bought an API unit from Sac City Corvette in California, with a 2 year warranty
for around $250(?).  Soon after installing it the engine would die when sitting at a traffic light in drive with
my foot on the brake. It was sporadic and only after the engine was warm. It would always fire right back up though,
and when driving, it was flawless. And if I increased the rpm while  my foot was on the brake just a little, or put it in neutral or park,
it wouldn't stall. Only in drive, at rest, when the rpm is lowest. This went on for a year and a half because
I was led to believe by a trusted mechanic that this sounded like a vacuum leak. I addressed every component
of the air intake except removing the intake manifold, which is original. Nothing changed.
Each time that the engine stalled the "service engine"  light came on but would go out after the car was shut
off  and restarted next time. I'm not a diagnostic mechanic. I am just good at taking things apart
and replacing or repairing if someone else tells me what is needed.

So finally, I got the idea to drive to a mechanic with an OBD1 scanner and wait there until it stalled for him
to read the code. Twice I did it and twice it said #26(?)...distributor. I ordered a replacement Opti since it was under warranty
and they were great about it and sent me a new one immediately after receiving the old one.
Put it on, and so far, it no longer stalls. (after one day.....but thats huge!)

I am posting this in hopes of helping other novices like me. Everyone said it didn't sound like an electrical
problem because it seemed related to RPM....turns out it was electrical.

I may not look here again right away at the forum, so if you ask me questions they may not get answered
right away. I just wanted to add to the pool of knowledge of the LT1/Opti issues. Thank you for being here, all
who make this forum happen.

Roadsurfer

Gainesville, Florida

Any time the Service Engine indicator lights, a code is stored. Even if the indicator goes out on the next ignition cycle. Reading codes should be the first step in troubleshooting problems.

A friend of mine when through 4 optis before getting a good one.

I forgot to mention that I did have it scanned when the problem began and it was not storing any codes.

"" and it was not storing any codes.""

After the Check Engine indicator lit?

sometimes a code is only in the computer as long as the problem is there, so once you shut down and start back up to code is gone.

This is why a lot of dealerships and repair shops will not diagnose an intermittent problem unless the CEL is on. Just had a car I took to a dealership for someone else that would intermittently go into limp mode, got to the dealer no problem dealer had it for 3 days but couldn't replicate the issue so no repair was done.

Okay, to be clear .....the engine would die at a traffic light.
The "service " light would come on. I would turn the key and start it right back up and keep driving.
Each time it happened (intermittently) I was in no position to go and find someone with an OBD1
scanner at that moment to check it out. After that trip was over and the car shut off, when I would start it up again, the service light was gone....until next time....etc.. and when I did have it checked without any service light on, it showed no code.
Since the problem never actually stranded me, it was easy to keep putting it off, until one day I decided to drive it to the mechanic and sit in his driveway with the motor in drive and wait for it to stall and then check it right then with the service light on. each time it read opt problem.
But it also seemed to vary in rpm while sitting still in drive, sort of rpm surge a little sometimes, as if I tapped the gas. Everyone said "vacuum problem" by the symptoms. And since removing and sending in the optic was a project, I explored external air supply for leaks until all was exhausted and I removed the optic and got a new one...and no more problem.
I didn't give enough details in my original account of the problem here. Sorry. You guys are on top of it!

I would only install an Optispark that has the Mitsubishi module. In fact, I would trust a Mitsubishi module from the junkyard over any aftermarket module. Buy the after market Opti and replace the module with a Mitsubishi module.

Everybody with a 94-95 LT1 car needs to keep [You must be registered and logged in to see this link.] with them at all times. Then obtain or borrow a laptop and install EEhack on it.  Diagnostic gold mine.

I have seen the api/sac corvette optis fail. As stated, Mitsubishi sensor is the only way go.

I saw on line, a tpi manifold mated to a modified base set an lt1 drilled for a regular distributer. Not that I trust everything online. Is that for real? Would the be a valid reason to do that, other than getting views to raise advertising revenue...
Claim was a ton more torque.

Isurf, you could do that, but a much better route for the same price is to convert to the LS-style coil-near-plug ignition system. At this point, it's cheaper than a new OEM optispark if you're willing to do some junkyarding. [You must be registered and logged in to see this link.]

Has anyone done, or heard about how good it is, the MSD crank trigger and PC programmable controller?

Not cheap but not many options beyond an LS conversion.

Sherloc9c1, I was not so interested in the distributor change as I was in the massive increase in torque with the much longer runners.

Isurf wrote:

Sherloc9c1, I was not so interested in the distributor change as I was in the massive increase in torque with the much longer runners.

While I am a big fan of the TPI style long runner very closely matched, 24" total runner including the heads IIRC, on heavy street cars, I do wonder a bit about a "massive" torque increase on a stock LT1 that already has 330 ft lbs. Of course we do not know how well a stock LT1 manifold would do replacing a TPI manifold on a Vortec, and we also don't know how much the reverse flow cooling contributes to the power output in our engines compared to stock flow direction. My guess would be that the LT1 manifold gives a flatter torque curve and if the TPI has a higher peak anywhere it would be quite a narrow rpm range, as that is normally how tuned intake systems work, but they lose out some on both sides of that peak.

The short small runner LT1 manifold does a very good job of producing torque. Better better than I would expect it to, actually. My only other personal experience with a short small runner was with a Victor Junior carb manifold manifold on on a Chrysler 340 engine on a twin turbo 340 I built in the late 1980s and it also produced extremely good power, especially low midrange. It had a similar camshaft profile to the LT1 engines we have because it was a turbo engine that don't like overlap. The Victor Junior's downfall was the huge runner length mismatch and the fact it was a carb and was pulling from richer and leaner barrels of the spread bore Holley carb. The engine was still on open chamber heads then so very prone to detonation and the leaner cylinder would backfire under boost and blow headgaskets. If not for that issue the Victor Junior that had runners similar runners to the LT1 manifold would have been a runaway top choice for that engine.

Can't say the guy is wrong on it, though, as none of us have seen the or ridden in the car, but I do know that the psychological issue of perceived improvements after modifications to our cars is very, very real. Been there.