There have been numerous posts regarding missing, sputtering and skipping when the engine reaches operating temp but I have not seen any real resolution. Some point to the opti some to the ICM and Coil. I have not read what actually fixed the problem.

I have a similar problem on my 93 LT1. When cold it runs great and I can predict when it will start to sputter by watching the engine temp. Depending on the duration of the ride it may take a bit longer to start acting up but between 215 and 230 degrees it will start to choke.

Last night was the worst yet. On my way home from work it started at the usual time but kept getting worse. It got so bad I couldn't keep up with traffic and was worse on any uphill grades. I noticed that the tach would go to zero each time it would sputter and then it would recover. Essentially the engine was dying and catching, dying and catching over and over again.

There have been suggestions to look at the injectors, fuel pressure, opti, icm, coil, etc... Before I take my wallet to the nearest parts store and start throwing money at the problem, has anyone experienced this and fixed it?

Logic tells me that this is not a fuel problem. Fuel problems don't usually turn on and off in rapid succession. If it was a problem with the injectors would I see the tach go to zero and then immediately recover?

I suspect the ICM/Coil but I would like some confirmation. Has anyone ever resolved their sputtering problem by replacing these components? Can the auto stores accurately test a ICM/Coil that only fails when hot?

Any and all input would be greatly appreciated...

 

Any codes?

 

My first opti acted up like that after car reached a certain temperature with no codes. Hopefully its not.

 

Okay, here's what I got for the codes shorting out pin G/A and reading the display.

Module 1- H72, H74
Module 4- H32
Module 9- ---

Any clues here? I pray it's not the opti. I can't deal with that type of repair right now. I am using the vette as my main source of transportation because the new car I have on order is two weeks overdue.

I can't take the vette out for service right now.

Tonight, I drove home easy and cranked the heat. Yes, it was 92 outside and I was cranking the heater. Temp remained under 210 for the entire ride home. I was able to get home without issue but there were times it would act up.

After I let it sit in the driveway for awhile I started it to put in the the garage. Temp was now up to 230 and it was missing/sputtering like crazy.

When this is happening is there any diagnostic checks I can do that would pinpoint the failing component(s)? If it is the opti wouldn't it throw a code?

 

32 is EGR 72 is Gear selector switch and nothing on 74. You can find this info under www.corvetteguru.com and go under tech info then engine.

 

I have the exact same issue on my 94. I have gone through everything trying to avoid the opti. ICM, Coil, Coil wire (it was arching), fuel pressure, datamaster scan shows sensors are ok but I get major spark retard when it acts up. I'm resigned to to it being the opti. It doesn't normally throw codes but one time it was particularly bad and throw a bunch of spark related codes. Fortunately, it isn't my DD so I haven't dug into it yet.

I agree... there never seems to one thing that causes this. I have been researching this for about 3 months now.

Good luck

 

You should be able to have the ICM and coil tested at Autozone or such. I recently did not have any luck with getting the ICM tested (they didn't have the connector), but did have the coil tested. Check the coil wire coming from the coil to the opti. They have a tendencey to shaf the insulation and ground on the water pump bracket.

At night with the hood lights off, run the engine and watch for sparks around the plug and coil wires. You may want to use water out of a spray bottle to enhance it a little.

Have you checked the fuel pressure or ohmed the injectors?

 

Are you getting any back firing up through the intake? Bad opti will cause that as well. Just got done replacing mine. How many miles on the Vett and have you washed the engine lately or had any coolant loss?

 

Check the coil wire coming from the coil to the opti. They have a tendencey to shaf the insulation and ground on the water pump bracket.

Sounds like bad wires resulting in the "electrical creepycrawlies."

The coil wire should be wrapped in a 6" section of corrugated, plastic, flexible tubing the way it came from the factory.

It helps prevent wire chafing and premature wire insulation breakdown from the intense engine heat in that location.

You can get it at any auto parts store.

 

"Have you checked the fuel pressure or ohmed the injectors?" No I have not checked these yet...

"How many miles on the Vett and have you washed the engine lately or had any coolant loss?" There are ~90k miles and I have not washed the engine or the engine compartment. Reading this forum I know better. I am not loosing any coolant either. The water pump is dry as a bone and there is no evidence of dripping on the garage floor.

I made it into work today without it acting up. Coolant temp ~207, Oil temp ~212

I can't find a new ICM in stock locally and only one parts store has a coil. The ICM and Coil are covered in road grime so at the very least I plan to remove, clean, reapply some Heat Sink grease and reassemble. While their out I will see if my Autozone or Advanced Auto can inspect/test. I am concerned they will test okay cold since I never have an issue when the engine/oil is at or near 200. It's when I get into the 220-230 range in stop and go driving that it happens.

 

I would suspect the ICM myself. It's the most likely candidate to my mind because your missing ONLY happens when hot.

An idea: Get ahold of a can of 'Freeze-it" (electronic stores carry that) and spray the ICM while running hot (after car starts missing). If the missing goes away you have your answer.

Cleaning the road grime off the ICM and coil is important also as that would act like a heat blanket.

Best of luck.

 

I've been dealing with this same issue myself for a while. But, the idea above sounds great to try. You think Radio Shack would have Freeze-it? It's definitely worth a try.

 

When my '92 did that a few years ago, it was the Opti-Spark.

There were no codes at all and the problem was intermittent.
It only happened after the engine would reach normal operating temperature.

The way I figured it out was by using a Tech-1A scan-tool and manually triggering a "snapshot" at the time it happened.
By graphing the snapshot, I could see that there was major knock happening and the ECM would attempt to retard the timing BIG TIME.

My guess, and it turned out to be correct, was there was a carbon track inside the Opti-Spark cap that was allowing the next cylinder in the firing order to fire 90 degees ahead of time.

Replaced the Opti-Spark and never had a problem again.
I now have a rotor-less Opti-Spark and a Delteq -- so, it can't happen again.

For me, the key to diagnosing the problem was the capability to take a snapshot (freeze 60 (30 before and 30 after the trigger point) frames of ECM data for graphing on a PC).


Tom Piper

 

I love the Freeze-it ideal too. I was trying to figure out how to cool down the suspect components without impacting others that may be bad. If I can cool down just the ICM/Coil and the problem persists then I can safely say (but reluctantly) it's the Opti.

I have been looking at the Delteq Opti-Elliminator too but I am reluctant until I know that the primary side of the opti is good and the problem resides in the secondary high voltage side. I'd hate to spend $700 only to find I have to replace the opti as well.

If my primary side of the opti was bad wouldn't it be throwing codes?

I am drawing on my old experiences when I say I am convinced it has something to do with the ICM/Coil, Coil wire, etc... Watching the tach when it happens its like someone put an inline rapid fire switch on the coil wire. If it was the opti wouldn't it be arching accross two cylinders causing a miss? This in turn would cause the tach to loose rpm's not go to zero. Similar to pulling a couple of plug wires. This only reduces rpm's, not send the tach to zero.

I realize I sould like I am talking myself into this... If I have to drive around for the next two months with a can of Freeze-it, so be it...

I think will do the trick... http://www.radioshack.com/search/ind...w=64-4321&sr=1

 

If the ICM is faulting, you should be able to determine that the first test with the freeze-it. No need to test over a period of time. Theoretically, it'll either work the first few times or it won't.

Another idea MAY be to temporarily unbolt the ICM and tie-wrap it away from the heatsink/bracket (therefore away from the hot cyl head) and see if there is any improvement? That may be something you could do tonight and have results by tomorrow morning? I'm not certain, but I don't believe the ICM needs to be grounded when you try this test.

Good luck.

 

my 92 had this same problem and it turned out to be the opti... it finally died of course in a bad place to pull over... Called AAA towing for a free tow... After this it did throw a code... forgot what code but it stated the opti...

 

Well I stopped and bought a can of Freeze-it on the way home from Radio Shack. I let the car sit and soak for a while so when I gave it a try it would be real hot.

Started it, it stumbled, I sprayed and nothing, no improvement. I wasn't convinced this stuff was actually cooling down the ICM since the heat is absorbed from the bottom side of the ICM so I started to take it apart.

Took out the ICM and coil and cleaned everything. I even splurged and bought a new coil for $20 at AutoZone. They didn't have an ICM in stock so I figured I would reassemble everything and see what happens.

Yes, I used heat sink grease on the ICM and the bottom of the sink before reassembly.

Fingers crossed, I started her up and went for a ride. At first all seemed well. I pushed it so that I could get the heat up and as soon as the oil temp reached 220 it started. Stumble, stumble, stumble all the way home.

By now it was dark and it was running terrible so I asked the wife to get in and bring it up to around 2000 rpms so I could check under the hood for lightning.

Sure enough and to my surprise the was faint arching on the passenger side plug wires where they pass through the clips that secure to the metal brackets. Both clips were arching...

We turned it off and I disconnected the clips and pulled the wires back away from the block. After restarting and bringing it back up to 2000 rpms the stumbling was nearly gone.

I took it for another test drive and by now the oil temp was 235 and no stumbling.

So I am assuming old tired plug wires that fail when hot? Reading the threads regarding the changing of plug wires on an LT1 I come to realize its not the best of jobs to do when its nearly 100 degrees and on a gravel driveway.

I have been contemplating going with the Delteq opti replacement. Wouldn't that eliminate the need to connect new wires to the old opti as well as eliminate another potential down stream problem?

 

With the Delteq, the plug wires do not connect to the Opti-Spark.

You will have to run them a different way completely.


If you go with the Delteq, it eliminates the high-voltage side of the Opti-Spark all together.
So, it won't matter if it is the Opti-Spark high-voltage side or the spark plug wires -- it should fix either one.

Delteq has the manuals available for viewing on their website.
I suggest downloading and reading the manuals.
Since you have a '93, you will have to bypass your tachometer filter following the instructions -- this is the part that sometimes gives people trouble. Not that it is hard to do, but it isn't just plug-in.



Tom Piper

 

Plug wires are not that bad to change. Hour or two, a few breaks and a few cold ones. Piece of cake.

 

Hour or two? Not mine.