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ecorti95 1992 Vette Misfiring intermittently
Guru Newb
5 Posts
Member since:
2009/8/23 12:55



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Corvette 1992, 73 K miles, bought it new, the problem is that it started misfiring intermittently a month ago. After driving for a mile or so, briefly misfires and Service Engine Soon, Service ASR, and SYS in speedometer blinks 3 times repeatedly. Also the AC stops cooling. The misfiring gets worse as the engine gets hot. I have been able to get home every time, but seems to be getting progressively worse. I do want to keep this car, it has been fairly reliable. I did have to replace the Opti and water pump at about 40 K miles. The car is stock, except an additional alarm was installed at the dealer when I purchased it.


I pulled codes from CCM Diagnostics, jumping Pins A-G in OBD1 connector

Module 1:

C41, H41 - Loss of ECM Serial Data Link


Module 4: No error codes, or sometimes if the car is hot it displays ERR


Module 9:

H62 - Tach Pulse malfunction

H72 - Loss of Data between CCM and EBTCM


ECM Diagnostics, jumping Pins A-B in OBD1 connector. Only display blinking code 12, or no reaction if there was a Module 4 Err when pulling CCM codes


I have read lots of posts from this and other forums, but I don't see a consensus about the cause of this problem based in the codes and pattern of misfires.

Some recommend replacing the ECM, some replacing the CCM, some indicate it is a wiring issue involving the Serial Data Link wires that are shorting, or grounding.


Can anyone provide some additional information that can help me troubleshoot and solve this problem?


Thanks in advance!
Posted on: 4/29 19:31
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CorvetteBob Re: 1992 Vette Misfiring intermittently
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1120 Posts
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2008/10/19 18:34



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While I’m not experienced with the LTx cars, I’ll try to offer a place to start.
These are free and just take some time, so be ready with flashlights and your thinking cap.
Just about every Chevy I’ve had eventually need the grounds cleaned. So I find every one I can and clean them regardless of appearance.
I’ve had cars with questionable batteries cause issues. Try a battery,if possible, from another car and see if it helps. I had a battery go bad that tested great, but my impala started having all kinds of electronic troubles. The battery trick fixed it. Also look at your battery’s connections. Our old suburban had the terminal connections all limed up on side terminals that aren’t sposed to lime up.
Back to connections, clean, clean, clean.
While you’re in there keep alert to anything that doesn’t look right. Greasy stuff on things, pinched wiring, anything you see that looks out of what you think is normal.
Finally, look for the presence of mice. That Impala I mentioned had been an inside car before I bought it. One day it would turn over but not start. Eventually the battery came out and I noticed something under the tray. Mice had gotten in there and eaten about three or four inches of harness.
I hope this helps.
Posted on: 4/29 19:55
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bogus Re: 1992 Vette Misfiring intermittently
Grand Imperial Pooh-Bah
San Pedro, CA
20618 Posts
Member since:
2005/9/7 0:00



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The C41 is worrisome to me.

That is the signal that goes from the engine controller to the chassis controller...

I think I know what is happening... but I am not sure and it would take a laptop to track it with software to monitor and record things. This would also require a USB connector to allow for communications to work.

I think Tunercat is the software you want, I will have to confirm, it's been a while.

However, it sounds like to me the ECM is shutting down or failing. I like the idea of making sure everything is connected and clean. Make sure the grounds are clean and that the power block (behind the battery, against the fire wall) is clean and all connections are solid.

There are many places where things can be corroded, especially near and under the battery.

Do all that minor stuff and then remove the plate on the bottom of the engine controller. Take a sniff. Does it smell like burnt electronics? If not, that's a good thing. If so, could be bad.

Take the controller and put it back, but don't put the cover on it. Get a can of air, like used on computers to clean dust off. Take the car for a drive, once it starts to misfire, pull over, flip over the controller, invert that can and spray the cold gas into the controller. If it starts running better, you have found the problem.

Other sources of this problem are a bad coil and/or ICM - Ignition Control Module. Also, a bad harness at the ICM will wreck havoc on things.

The ICM is on the right head. You can see the coil wire. This is the source of the spark.

If the engine controller seems ok, the next time it misfires, use the same spray on the coil/ICM. If things settle back down, there is the problem.

I am betting more on the coil/ICM vs the ECM.

If it is the ECM, unless things have changed, you will need to go used. 1992 and 1993 Corvettes share the same ECM. 1993 Camaro and Firebirds, with LT1, share it, too. And from my initial search, no love new... no one is remanufacturing these things.

Again, I would start with the ICM and coil. Depending on mileage, that would be a great starting point. I am guessing the car has over 100k, so yes, ICM and coil.

And don't be surprised it is the harness. They get greasy and rotten and stuff. It ain't pretty... Same goes for the harness to the opti itself.

touch base before buying anything. There are some upgrades you need to consider.

Posted on: 4/30 18:32
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bogus Re: 1992 Vette Misfiring intermittently
Grand Imperial Pooh-Bah
San Pedro, CA
20618 Posts
Member since:
2005/9/7 0:00



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Any update?

The more I think of this problem, the more I am convinced that the issue is with the harness around the coil and ICM.

Back some 15 years ago, a C4 regular on Corvette Forum had the exact same problem. His car would run great, then start to misfire. His was also a 1992/93 vintage.

After much analysis, it was found that the harness for the coil/ICM had failed and was intermittently losing connection, causing the coil to shut down for a moment, then turning back on. It was a needle in a haystack, to be honest.
Posted on: 5/7 15:54
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw

Education is the best tool to overcome irrational fear. - me

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CorvetteBob Re: 1992 Vette Misfiring intermittently
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1120 Posts
Member since:
2008/10/19 18:34



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I’m interested as well, any updates?
Posted on: 5/9 0:29
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