EDIT: PROBLEM SOLVED! It was the coil. For details see Post 40 on page 2 of this thread

I was driving my '92 LT1 six speed yesterday when this happened for the first time. Car was warm, and stalled unexpectedly as I released the clutch in first to pull away from a stop light. It started again right away, and I figured maybe I didn't give it enough gas and killed the engine, but then it did it again. Then when driving in different gears, the car stalled/cut out momentarily several more times. It just did it for a fraction of a second and the car bucked, but I did not have to restart it. Then later when driving home, about 30 miles, it had no problems at all. When it wasn't stalling the car ran perfectly... no miss, good idle, good acceleration, etc.

I know, everyone is thinking Optispark, Optispark, Optispark, and that may be the problem. However, the check engine light never came on and there are no codes set except for a CCM code 72, which is for the dimmer for the instrument lights. The lights work perfectly so I think that may be an old code. The Optispark and waterpump have about 40,000 miles. The coil and ignition module were also replaced in the last 40 miles or so.

Is there any way to figure out what's happening with out just starting to replace parts? I know that with the car running perfectly and no codes it's pretty hard to diagnose, but at this point I'm a little afraid the drive the car. Thanks for any help!

 

I had a simialr problem on my first vette, 70 LT1. Come to find out it was a frayed wire that would intermittently short out against the frame as the car was moving. You might check all your major grounds. Let the engine idle and try moving the various wire harness around a bit to see if you can duplicate the problem. Good luck.

 

Sounds reasonable. I did a visual inspection as best I could (LT1 spark plug wires, optispark, coil, etc. are not very visible) and didn't see anything. Like you said, it may be worth moving the wires around. Thanks Steve.

 

I have a 1992 LT1 6 Speed also , I experienced this problem a few years ago , My problem was a very very slight seapage at the water pump that was running down over the OPTI-SPARK Distributor , went for a long time before it left me stuck.

Try this take your car for a nice warm up ride , Park it on a level clean area (prefferably inside) . place a large white piece of cardboard or poster board under the front end , when the engine cools overnight check the area for ANY spots , mine had a minor drip under the crank pulley (Anti-Freeze) , which turned out to be more severe up where the distributor was.
When it would miss during warm up I had almost the identical problem you described , after it warmed up I guess the wires and cap dried out and it was ok all day. this went on for almost 2 months . then without warning my water pump blew out trashing my opti-spark distributor.
If this is your problem and you find a small coolant leak , maybe you can luck out with just a water pump and no opti....

Let me Know..

DESERT

 

Thanks Desert. You're right, it's worth checking the waterpump very carefully. I figure there's a chance it's not the Optispark just because it and the waterpump are relatively new and there are no codes. However, I guess you just can't tell until it totally stops running!

 

You don't always have codes for the opti...

Do you see any trails on the hood just above where the serp. belt rides? sometimes when the water pumps seep it will get on the belt and it will mist the coolant on the hood, you may not see it on the ground.

If you have access to a scan tool the data (check codes as well) can sometimes tell you alot.
-=Rick

 

Rick,

I'll check for a coolant trail on the hood. What data should I be looking at? Is there some data from the opti that can be monitored? Thanks.

 

The coil wire should have that ribbed plastic on it to keep it from rubbing against teh waterpump. Check to be sure the coil wire isn't touching the waterpump. That was my problem.

 

Thanks Mojo, I don't have the ribbed plastic protector so I'll check that again very carefully.

So far, I don't see any evidence of a waterpump leak and all the wires seem to be ok. I haven't driven it much, but during the time I have driven it there has been no hint of the problem. Maybe it just had a bad day, although I doubt it. I'm sure I'll deal with the problem again, most likely at the worst time possible!

 

Don't rule out the ICM going south. Mine died when I tried to start the car after replacing the Opti. It was NOT fun finding that problem.

Larry

 

some of the gt40 replica guys, sayd they had the same problem, the source was a bad ground on the ECU

could this be the same ?

 

ICM... are you referring to the ECM (computer) or the small ignition module near the coil? I've replaced both in the past, but I suppose either one could be causing this problem. Thanks!

 

I'm not sure. I don't know how the ECM is grounded, but I would think that if that's the problem, there would be lots of additional problems, as all systems controlled by the ECM would go out. I did check the ground for the ignition module, coil, and tach filter. It looks ok and I did clean it when I replaced the ignition module a couple years ago, but maybe it would be wise to take it off and clean it again. I'll probably do that.

Part of the problem with diagnosis is that everything seems to be fine now. I drove it almost two hours yesterday, even through heavy rain, and no problems at all.

 

its prob a bad connection some where down the line....
i must say i hate troubleshoting, and as you said everything always looks fine

 

Check your fuel pressure.

 

Good idea. I was wondering about fuel. I don't think the fuel pump has ever been replaced (140,000 miles). Can a failing fuel pump cut out intermittently? I don't see much on here about the LTx fuel pumps, so its seems like they're pretty reliable. However, that's a lot of time and mileage.

 

Also check you fuel filter. It's one of the most over looked filters. I just opened one up from my truck, it was full of metal(rust) pieces and sand .

 

Go for another drive and watch your coolant temperature readout when the bucking happens. I say this because my corvette is currently undrivable right now due to the same symptoms you're having; the car will buck and stall after a while of driving, then be fine for a while, then start bucking and stalling again. If I watch the coolant temperature while my car is doing this, I'll see it jump from hot to freezing to hot to freezing to hot, right in rhythm with the bucking.

Your computer bases the spark timing on how hot your engine is, and it uses the sensor mounted on the water pump to find that out. When that sensor just absoloutely goes nuts, the engine will change timing so fast that it becomes unroadworthy. Ask Bogus, he also had this problem. Just keep an eye on that coolant temp readout when it bucks to find out if it's causing it.

If it is, the sensor is only 12 bucks at autozone, but you have to drain the coolant to get it out. Like everyone says, there's a number of other things that could cause such a problem, but since your symptoms match mine exactly you ought to give this a try.

 

I did replace the fuel filter about 3 years/20,000 miles ago, but it's certainly a possibility. If it comes down to replacing parts and hoping for the best, that's certainly one of the cheapest (although least fun) to replace!

 

Interesting. I'll set the display to coolant temp from now on and keep an eye on it. Thanks!