My 95 has run fine until an oil leak saturated the Optispark. The leak was repaired, new Magnecor wires and plugs installed and all the oil cleaned. I had expected the need for a new Optispark but once cleaned, it ran great. Except for one thing. If you drive at a given speed say 50mph for 2 minutes and then either floor it or press the accelerator down at a good pace, it stumbles. The car is a manual and you can accelerate hard through all gears and she never stumbles.

Any ideas? The shop that has her suspects the Throttle Position Switch.

 

Could be the TPS, but I'd also OHM the injectors. The Rochester Multec's are known to have a short lifespan.

 

How did you clean the Opti?

 

I don't know how the Opti was cleaned. My car is with a local shop that does a good amount of Corvette work so I would ope it was cleaned properly. The shop owner said they have had to clean Optispark many times and he was actually calling me to say the car would be ready lat in the day. He then called back to say all was fine except the stumbling that he had not had on any prior car with my oil leak problem. It does idle and drive 100% except for the noted stumbling. I've driven it myself and it is odd.

 

Highly doubt it's an opti problem.

Sounds more like a vacuum problem, or fuel related.

Could be the TPS, or the FPR could be starting to go.

Does it stumble if you downshift to accelerate?

Or stumble revving at idle?

 

We assume that there are no codes to download...... from afar, I'm betting on a failing opti, but hope I'm wrong.

 

There are no codes showing up and at idle it fine. If you downshift and accelerate hard it's fine too. The only time there is a problem is driving for a bit at a steady speed and then flooring it or accelerating hard. Mits then that it stumbles.

 

OK.. so in your opening statement;

"My 95 has run fine until an oil leak saturated the Optispark"

What oil leak? Did the Shop remove the Opti or just blast it with Brake clean? If they removed the Opti a plug wire may have gotten damaged do to age..

 

He said the plug wires were replaced..

 

There were a few lower engine oil leaks. The one effecting the Opti was a seal just behind or just above the Opti that leaked right onto it. The leak occurred whenever there was oil pressure so every time it was running. It's so odd because other than this one scenario the car runs great. The shop removed the Opti to clean it. They said it was saturated. I thought it was going to be time for a new one or the Opti v. MSD debate in my head.

 

Being a skeptic, I doubt the shop removed the opti to clean it. Probably just applied a cleaner, and a rub down. I strongly doubt the opti was removed for internal cleaning. The outside of the opti is not the problem..... it is what enters the opti that causes problems, whether it be water or oil.

You will be able to tell by the bill amount if the opti was removed. To get to the opti, the water pump has to be removed, and labor cost could be in the 6 hour range.

Failing optis do strange things, and one symptom is a miss under acceleration. Again, I hope I'm wrong.

 

I will hope you're wrong too. If they did actually take it out at 6+ hrs and reinstall it and now I have to pay 6+ hrs plus the cost of a new one to put in I will be beyond unhappy! I know they never mentioned a new water pump (which would make sense if the old one had to be removed ). So perhaps you are right that they simply cleaned the Opti and never actually took it out. Here's to hoping!

 

Well you were right. The Opti was not actually removed to be cleaned. The shop is putting in a new TPS tomorrow to make sure that isn't the problem. If it isn't then it's new Opti time! Oh well. I can hope but I know where this is going.

 

You might want to start a new thread asking for replacement opti recommendations. Probably every opti on every C4 produced from 1993 has had the opti replaced. Several manufacturers of replacement optis have gone out of business, but there are still several choices.

Some owners with 20 years of opti experience may be able to direct you to a reliable solution.

 

Now we are getting somewhere.. how many miles are on the Opti?

 

I'm still on my original at 153K miles. It has survived a water pump leak, a radiator hose burst, and what not. Though I did have a new cap and rotor installed with the hotcam at around 85K. This was well before the rad hose burst.

I'm not saying the opti isn't the problem here. I am saying that there can be alot of other things that would cause this symptom that is much easier and cheaper to fix, that combined with the fact that a fair amount of replacements are of questionable quality, replacing the original opti should not be done unless absolutely neccessary.

First, the TPS is something to check. Fuel delivery as well. The first and easy check is the FPR, pressure the system and pull the vacuum hose, if it's wet it needs replaced. Even a clogged PCV can cause this. Fuel filter, fuel pump.

What I find curious, is that the only symptom is hesitation when going full throttle while cruising at 50 or so, w/o a downshift. IDK, I always downshift for wot acceleration but I know what you're talking about. I have to throw this in the mix, perhaps your DMF is going out of spec? In other words, you're putting alot of load on the FW and the spring might be a little loose and so there is some lag between the engine rpm and the transmission rpm? This I guess would depend on what gear you're in when you do this, but at 50, if you're in fourth, that would put some load on the FW.

The thing I trying to get at is that the only time, according to the OP that this problem exists, is under heavy load acceleration. Apparently revs fine in neutral, and operates normally otherwise?

Kind of reminds of the that old joke: Patient: "Doctor, it hurts everytime I do this..." Doctor, "Well, stop doing that".

 

Well it was the Opti that was on its way out. The car has 124,000 on it and since I'm not the orig owner I don't know haw many miles are on the Opti. But in trying to look at the bright side, I have new plugs, my Magnecor wires ive been putting off for a while and I also have a brand new water pump to help with August in Georgia! I think that and the fact the car is running great are good things. This forum has been helpful each time I have a problem. Thank you all very much.

My problems are always question marks because my LT1 and computer are from a 95 vette but are installed in my 95 Porsche 968. One day I have to figure out how to post photos so I can share some.


Ron B.

 

So did you replace the Opti or did you got MSD?

I have similar stumbling on my 1990 L98. I swapped out the TPS...no change. One odd item (what pointed me at a sensor) was that I could pull over and stop the engine, restart and the problem would be gone for perhaps a mile or so. Then the stumbling would return at 2K+rpms. Did you try stopping and restarting the car?

Rex