LT1 Stalling/Cutting Out SOLVED
 

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.:thumbs:

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. :thumbs:

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 :rolleyes:

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 :eek:.

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!

I certainly don't want you to throw parts at it. It could be anything to be honest. You will need to diagnose everything that can cause this issue. It would be nice if some sort of code would pop (CEL).

The shop manual says there's no service interval for the fuel filter, so the only time you would ever need to replace it is if you fuel gets contaminated. I'm checking mine soon, but only because I am suspicious that someone poured sugar in the tank.

Ok, it started acting up again yesterday. Cutting out on the freeway. Both times it did it (yesterday and about a week ago), it was only after about 20 miles when everything had warmed up and it was also above 80* outside. I have a 160* thermostat, and the car was running at about 190*. When it was cooler outside and it did NOT have any problems even after driving a while, it was only running at about 175*. In other words, I've had the stalling and cutting out ONLY when the engine temp is above about 185*.

SO, I'm starting to think it's temperature related, although I still haven't driven it enough in different temperatures to be sure. Still no codes, and the temperature sensor seemed to be working perfectly. I had a problem with the ECM a while back that was temperature related, and replaced the ECM with a remanufactured unit. That was a few years ago, and I know they're not that reliable. Therefore I suspect the ECM. I touched it after driving and it does get pretty hot from being in the engine compartment. I'm going to try to find a hairdryer or some way to warm it up and try to test my theory.

Ryan..I was reading through your post again. I agree with you that it is probably heat related...and I noticed that you said that you had r & r'ed the coil and coil module awhile back. Did you use fresh grease on the back (against the flat mounting plate) to prevent heat sink? Those suckers are known to fail with load and heat. Just a thought....

Steve,

Yes, I did use the grease that was supplied with the new coil module. I actually replaced the old one a while back because the car stalled once and gave me a code that I traced to the tach filter and coil module. I replaced the module more as a preventative step and I kept the old one which should work ok for testing purposes. Couldn't hurt to switch the old one back in and see what happens I guess. Now I just have to find it! Thanks!

Man, this really really really wreaks of the opti and that is where my money is at.

:iagree:

I don't disagree, but it'd be nice to have a way to be more certain before I change the opti and waterpump and hope for the best. Seeing as how there are no codes (opti usually sets code 16) and the opti is fairly recent, I'm just not that sure.

On my 94Z, you described the symptoms to a T. No code either and a bad distributor/cap is sensitive to heat.

Do you have an Autoxry or other data gathering device? YOu might leave it hooked up to the ALDL when your driving. When the car acts up again, you could take a "snapshot" of your sensors to verify they are all with range. That would also tell you what the ECM is 'seeing' from them at that time.
FWIW..the car will run with a code 36 from the opti...even if it is a soft code.

I'm in the process of getting an Autoxray. I know it can monitor sensors, but what about the opti? Is there any data from the opti or related to the ECM that would be helpful?

On the code 36... isn't that something that would be stored in the computer? I didn't get any codes except that code 72. Also, what's a soft code?

You'd need another type of scanner to monitor the opti output. I was suggesting the Autoxry to be sure all your sensors (and what the ECM was seeing) weren't malfunctioning.

A soft code will register with the ECM but will not keep the SES light "on". It is an intermittent code and may be purged from the ECM after a certain # of start cycles without the problem recurring. Have you tried to pull codes right after the car acts up? You may very well have a opti problem but throwing $ is at best a hit and miss proposition. A fuel pressure guage taped to the windshield (and a short ride) would help eliminate FP problems.

Ok, still giving me the same problems, but only when it's hot so it's definitely temperature related. Drove around with the Autoxray connected when it acted up. Everything looks normal EXCEPT that when it cuts out or dies, the SPARK ADVANCE goes to 5 degrees (from a normal of 20-25 degrees at idle) and the DESIRED IDLE goes from 662 to 1387 RPM. Actual idle RPM does not change.

Does this mean anything to anyone? To me it could be anything... just symptoms of an optispark problem or possibly the ECM doing something weird with the spark advance and killing the engine. :crazy:

I am having this exact problem with my '95 and am listening intently. Mine has thrown the code:

"DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High."

twice after symptoms. My temp goes to 230 (normally 197 to 201) with a rough idle before the "bucking" as you describe. I noticed for the first time today the digital temp bounce momentarily from 215 to 145 a few times as these symptoms were raging.

I think I am going to change out the Temp sensor and see if that does the trick, but am very interested in more diagnosis. Sounds a little too common for there not to be a good answer. Don't think it's fuel.

:bigears :bigears :bigears :bigears :bigears :bigears :bigears

Come to think of it, my analog guage has a "flutter" sometimes. Looks like a loose ground or something, and I never thought much of it. Sometimes, especially when cold it just kinda acts crazy, the stabilizes as the heat builds. Cound this be a sign of a bad sensor, and a bad sensor causing the problem, or is it just all unrelated????

Hmmmm.....

:willy: :willy: :willy:

Sounds like the coolant temperature sensor is causing your problem. In page one of this thread, member LouisvilleLT4 said his coolant temperature sensor failed and caused his car to do the same thing. Coolant temp was all over the place just like yours. Looks like you probably found your problem. :thumbs:

I'm not so lucky. My coolant temperature has never wavered, so I think my problem is something else. It's supposed to be 90* here this weekend, and I'm gonna go out and drive the car until it dies for good so I can figure it out! I'm tired of this intermittent BS. Hopefully by the end of the day on Saturday I'll need a towtruck! :crazy:

Changing the ECT completely eliminated my problems. I changed the sensor and the plug, and they both looked fried.

The sensor must somehow effect the analog guage, since the guage "flutter" that is always had had also been eliminated. I did not do anything but the sensor and the plug.

Since this is a quick, easy and cheap repair, I would suggest changing the ECT, and see what happens.

:thumbs:

While we're still talking about this, I'll mention that I recently changed out my ECT sensor and my car is still having this problem. It seems, however, that I can trigger the problem by wiggling the wires where they go into the sensor. So for anyone with this problem, be sure to diagnose your wiring well before you go replacing sensors.

So anyway, I bought a new pigtail and am in the process of figuring out how to splice it in without adversely affecting the circuit's resistance. Any advice is appreciated.

I changed the plug and sensor at the same time. Both looked fried and there were missing peices off the plug.

The new pig tail should come with about a 12 inch lead, so just cut and splice. I used butt connectors, but really should solder the connection and heat shrink it. i just didn't have any solder and heat shrink, so I will eventually redo that connection.

Easy and basic.

:thumbs:

Problem Solved
 

I'm happy to report that I fixed the problem. Hopefully this entire thread and the solution will help others who may have this problem in the future.

After checking all the obvious and not finding any problems, I gave up and took the car into a local dealer with a good Corvette service guy. They drove the car with a Tech 2 connected, and got the car to replicate the problem. However, it wasn't doing it badly enough to show them anything on the Tech 2. They were fairly certain it was either the coil or the optispark, although both of those parts were relatively new. Well, the opti is an expensive part that takes a lot of work to replace, whereas the coil is cheap and easy. I figured I'd take a chance and replace the cheap and easy part first and see if that would do it. So I bought a new AC Delco coil at the dealership and put it in myself.

The Corvette gods must have been smiling on me because that seemed to fix it. I drove it about 60 miles yesterday in temperatures approaching 100* here in Phoenix, and the car had no problems whatsoever. Not even a hiccup. So I'm confident that the coil was the problem and it's now FIXED. :hurray: :hurray:

Congrats on finding the fix. Glad it wasn't the opti. So it was the coil. I think I mentioned that a few posts back....:D Sorry Ryan, I just had to say it.........

You gave me a wide variety of good suggestions Steve. One of them had to have been right! :lol:

:rofl: :thumbs: :cheers: