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1992 Corvette No Spark Diagnosis
- jackson.lanich
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7 months 6 days ago - 7 months 6 days ago #65159
by jackson.lanich
1992 Corvette No Spark Diagnosis was created by jackson.lanich
I bought a 1992 Corvette a year and a half ago. Wouldn't start. The previous owner said it was the optispark and didn't have the time or expertise to fix it. We got it and began looking for the problem and decided to replace the optispark. I did it outside in a gravel driveway. Finished it and still no spark. Everyone on the Corvette forum said to do the ICM and the Coil next. We replaced the fuel pump and was getting pressure. Was getting ECM code 41. We replaced those two parts and still got nothing. Took the car inside since it was getting cold. Worked on it and one day after going through the FSM diagnostics for code 41 and got nowhere. We got the ECM rebuilt and nothing happened. One day it decided to start. Awesome!!! It barely could stay running and after putting it in drive and going 20 feet it died and wouldn't restart. Wouldnt even go on starting fluid. Pushed it back inside and after hearing it we decided to check compression. It was really bad on over half the cylinders. We had the engine rebuilt and got it back excited to get it to run. Put it in and got everything connected and no spark. Went through everything. This was in January. Went through the FSM. Checked fuses, grounds, and power. This is when I found the video. Followed it as close as I could with a multimeter and test light. I couldn't pinpoint it and I thought maybe one of the signals looked weird and caused it not to work. I put a known good ICM on and it didn't do anything. I then ordered a Hantek 1008C from Amazon and hooked it up to the car. Its a great tool and showed me that the ECM is sending a square wave to the ICM at 5.05 volts. Looked exactly like the video. All the power looked good and didn't drop too bad. I then looked at the signal going from the ICM to the Coil. This is what I am stuck on. The groundside circuit looks like a wave, and I attached a picture. In the video it looks sharp and a really big drop. Its been 3 months of working on this. I dont think it is the opti or ECM. I also put a new Coil on it today and put another known good ICM from another car on it. I'm stumped!
Codes!!!
CCM Codes - C41, H41, H72
ECM Codes pulled from CCM - ERR
ASR/ABS - H72
From the codes, I think I have a problem in the serial communications, but I would that I would have a no crank issue and not a no spark since what I said up top earlier.
Any help would be appreciated!
Codes!!!
CCM Codes - C41, H41, H72
ECM Codes pulled from CCM - ERR
ASR/ABS - H72
From the codes, I think I have a problem in the serial communications, but I would that I would have a no crank issue and not a no spark since what I said up top earlier.
Any help would be appreciated!
Last edit: 7 months 6 days ago by jackson.lanich.
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- ScannerDanner
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7 months 6 days ago #65162
by ScannerDanner
Don't be a parts changer!
Replied by ScannerDanner on topic 1992 Corvette No Spark Diagnosis
Your picture is coil negative voltage?
That's not right.
What is your voltage scale set at?
Take a capture of coil positive voltage too please.
That's not right.
What is your voltage scale set at?
Take a capture of coil positive voltage too please.
Don't be a parts changer!
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7 months 5 days ago #65173
by jackson.lanich
Replied by jackson.lanich on topic 1992 Corvette No Spark Diagnosis
I checked all the wires coming in and out of the ICM and coil with the oscilloscope. ICM wires A (power in) and D (coil driver) both have the same signal. Wire B (ECM signal in) has the 5 volt square wave (image below). C is ground and has no signal. All 4 wires on the coil have the same signal in the image below. I attached a diagram of the ICM and Coil wiring. For all readings except ICM wire B I used 20v with the x10 setting with a time of 500ms. Thanks!
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7 months 5 days ago - 7 months 5 days ago #65174
by ScannerDanner
Don't be a parts changer!
Replied by ScannerDanner on topic 1992 Corvette No Spark Diagnosis
There is no coil negative control going on there but it should be. That icm is not doing its job. Make sure the icm body itself has a good ground.
Scratch that the icm has an external ground, make sure that pin is not spread apart.
If that is good, get another ICM, BUT make sure your ignition coil primary winding isn't shorted (which would kill a new module)
Scratch that the icm has an external ground, make sure that pin is not spread apart.
If that is good, get another ICM, BUT make sure your ignition coil primary winding isn't shorted (which would kill a new module)
Don't be a parts changer!
Last edit: 7 months 5 days ago by ScannerDanner.
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6 months 3 weeks ago #65360
by jackson.lanich
Replied by jackson.lanich on topic 1992 Corvette No Spark Diagnosis
Ground appears to be ok. I picked up a new ICM and it didn't change a thing. I tried closing the contacts on the connection and that also didn't do anything. After that I checked for continuity on all 4 wires between the connector and where I was pulling the signals on the oscilloscope and everything was good there. As an effort to see what was wrong I put a ICM on a Impala and used a spare optispark to send the signals since it doesn't have a starter. Every single signal looked perfect and it was even getting spark. I am completely lost and can't find any info on what to try. I would like to fix it myself but it has been a year and a half and starting to think about taking it somewhere.
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6 months 1 week ago #65482
by jackson.lanich
Replied by jackson.lanich on topic 1992 Corvette No Spark Diagnosis
Here is an update for the thread. We decided to contact Corvette Care in Columbus, Ohio. They said it sounded like a bad optispark and ALL of them are junk except the MSD Pro Billet and they wouldn't work on the car unless it had one in it. I got one and need to finish the install. I will keep the thread updated with what happens!
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5 months 4 weeks ago #65584
by jackson.lanich
Replied by jackson.lanich on topic 1992 Corvette No Spark Diagnosis
Another Update. MSD Pro Billet Opti install. It requires a new optispark wiring harness. One was available from Summit. Installed it and gave it a quick crank after a shot of starting fluid. The engine "caught" and sounded like it wanted to go. I put everything back together and went to start it. No spark. Interesting thing is that we originally had no tach signal and when it was installed, we had signal, and the needle was jumping around. Then it stopped after a few more cranks and nothing. Back to the same problem. Program on PC says we are getting 125 RPM when cranking. Don't know if it is right but we had more on the tach gauge than that when it worked. Looking into tach signal diagnosis but everything says to do what we already did and hang even more parts on it.
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5 months 3 weeks ago #65588
by Lupe
Replied by Lupe on topic 1992 Corvette No Spark Diagnosis
how about your distributor and your rotor to match your opti and to be on time. good luck
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