92 Cavalier ignition system.

[wtd]

Is anyone here familiar with the ignition system on this car with the 2.2L. I just had to replace the ICM for the third time since early 2018. I also had to replace one coil. I had to replace the ICM one other time years ago and it lasted almost 100,000 miles.

I'm not sure why these keep going out. This last one only lasted about a year and a half and about 11,000 miles. When I replaced it in 02/2019, I also replaced both coils, plug wires, and plugs. I used a Standard ICM and coils with lifetime warranties.

I recently cleaned and tightened all of the grounds on this car. Any ideas on what I should be looking at that may be causing these to go out so soon would be appreciated. Thanks.

 

[slacktide_bitog]

Use OEM parts, not cheap aftermarket.

 

[Chris142]

Any ideas on what I should be looking at that may be causing these to go out so soon would be appreciated.

Short in a harness or sensor.

 

[mk378]

Those 4+2 wire distributor mounted ICM's just don't last. Always carry a spare.

When I had a car that used one I could blow them reliably by flooring the gas pedal to get on a freeway, then suddenly releasing it. So that's a "Doctor, it hurts when I do this" thing and the best plan is don't do that.

I think it results from high resistance in the spark circuit, so make sure your plugs, wires, cap and rotor are in good condition. Especially the wires.

 

[Jethro_Bob]

I read this somewhere online, never had to replace one, so I never tried it. Use thermal grease, the kind for desktop cpu's on the mating surface.

 

[Yah-Tah-Hey]

I read this somewhere online, never had to replace one, so I never tried it. Use thermal grease, the kind for desktop cpu's on the mating surface.

1976 Chevelle 350 owned ten years with 80K+ still had original unit when sold.

 

[wtd]

This car has no distributor and I always use dielectric grease between the ICM and the aluminum mounting bracket. I bought an AC-Delco ICM years ago and it didn't last either so I'm not sure if the OEM replacement parts are any good either.

All of the wiring looks good from what I can tell but who really knows.

Right now I'm running one of the original coils in place of the coil that went out but I did get a new warranty replacement today.

 

[ms21043]

Plain dielectic grease is an electrical insulator. Thermal paste is similar but has fillers that make it conductive and help transfer heat. I would use thermal paste or whatever comes with the ICM if anything.

 

[wtd]

Plain dielectic grease is an electrical insulator. Thermal paste is similar but has fillers that make it conductive and help transfer heat. I would use thermal paste or whatever comes with the ICM if anything.

Nothing came with the ICM and in the instructions on installation it doesn't even mention putting any type of grease between the ICM and mounting bracket. I will have to find some thermal paste for the next time I have the ICM off. Thanks.

 

[clinebarger]

GM DIS modules didn't use Thermal Paste from the factory like the GM "HEI" modules did. But.....It's still a good idea to use a VERY thin layer of it!

Corrosion between the ICM & it's mounting bracket will reduce the modules ability to shed heat.

A shorted coil/plug wire/spark plug can take out a ICM pretty quickly.

A shorted to ground Tach Circuit can make the ICM appear dead, Then a new ICM gets installed & the harness is moved just enough to un-short the Tach Circuit.....Even cars without Tachometers have the circuit in the harness.

 

[wtd]

GM DIS modules didn't use Thermal Paste from the factory like the GM "HEI" modules did. But.....It's still a good idea to use a VERY thin layer of it!

Corrosion between the ICM & it's mounting bracket will reduce the modules ability to shed heat.

A shorted coil/plug wire/spark plug can take out a ICM pretty quickly.

A shorted to ground Tach Circuit can make the ICM appear dead, Then a new ICM gets installed & the harness is moved just enough to un-short the Tach Circuit.....Even cars without Tachometers have the circuit in the harness.

Thanks for this info. Coils, plug wires, and plugs were all new when I installed the one ICM in Feb of 19. I also used a small brush on my dremel tool to totally clean the aluminum mounting bracket. I don't remember for sure if I cleaned the block where the bracket actually mounts but I think I did.

I do remember that right before I removed the ICM/coil assembly from the car after I had tried testing for spark to the plugs, that the cylinders 2&3 coil felt warm compared to the other one which was cool.

The wiring harness going to the ICM is very hard to see because this car has an automatic transmission which gets in the way. All of the wires that I can see look ok but that doesn't always mean they are.

I did replace the short wiring harness that goes from the crank position sensor to the ICM with another one I had because the one on the car was wet with oil from the leaking O-ring on the crank sensor and there was a little bit of oil down in the well on the ICM where the crank shaft harness plugs in. I don't know if the oil could have caused some issues or not. For now, the car is running again. I replaced the plugs again with a set of AC-Delco double platinum replacements for this car instead of the standard copper ones in hopes that the platinum plugs may not be as hard on the ignition system. Hopefully it will stay running longer this time.

 

[wtd]

Well, I went to the store yesterday and the CEL came on and car was running a little rough. On the drive back home the CEL was off and the car seemed to be running fine.

Put the scanner on it when I got home and it had a code 42 which is an Electronic Spark Timing code. This code can be caused by open or shorted wires, bad ECM, or bad ICM. I did the tests in the flow chart out of the factory service manual and ruled out the ECM but not any of the other things.

Even though the CEL is still not currently on, the code is still stored in the computer even though the scanner says the code was successfully cleared. I'm not sure if I have to unhook the battery to fully clear the code or that the code is still setting somehow without turning on the CEL.

I guess it's possible that the ICM is again messing up. Not sure what to do at this point. The car has been driven several hundred miles since the ICM and coil replacement with no issues until yesterday.

 

[clinebarger]

You need to unhook the connectors & drag the harness up-top for close inspection of the ICM wiring, I realize this is a PITA! Oil will literally eat the insulation right off the wiring causing intermittent shorts.

Intermittent loss of the Crank Position Signal to the ICM will cause a DTC 42, The ECM just knows that it lost the Reference Pulse from the ICM. You'd really need a 2 channel scope for this to see if the CKP signal dropped out at the same time as the Reference Pulse or not.



The EST system is basically the same EST to ECM circuit used on the distributor type ignition systems with EST. This system includes the following circuits:

• DIS Reference (CKT 430) - The crankshaft sensor generates a signal to the ignition module, which results in a reference pulse being sent to the ECM. The ECM uses this signal to calculate crankshaft position and engine speed for injector pulse width.
• Reference Ground (CKT 453) - This wire is grounded through the module and insures that the ground circuit has no voltage drop between the ignition module and the ECM, which can affect performance.
• Bypass signal (CKT 424) - At approximately 400 rpm, the ECM applies 5 volts to this circuit to switch spark timing control from the DIS module to the ECM. An open or grounded by pass circuit will set a code 42 and result in the engine operating in a back-up ignition timing mode (module timing) at a calculated timing value. This may cause poor performance and reduced fuel economy.
• EST circuit (CKT 423) - The DIS module sends a reference signal to the ECM when the engine is cranking. While the engine is under 400 rpm, the DIS module controls the ignition timing. When the engine speed exceeds 400 rpm, the ECM applies 5 volts to the bypass line to switch the timing to the ECM control (EST). An open or ground in the EST circuit will result in the engine continuing to run, but in a back-up ignition timing mode (module timing mode) at a calculated timing value and the SERVICE ENGINE SOON light will not be on. If the EST fault is still present, the next time the engine is restarted, a code 42 will be set and the engine will operate in the module timing mode. This may cause poor performance and reduced fuel economy.

 

[wtd]

You need to unhook the connectors & drag the harness up-top for close inspection of the ICM wiring, I realize this is a PITA! Oil will literally eat the insulation right off the wiring causing intermittent shorts.

Intermittent loss of the Crank Position Signal to the ICM will cause a DTC 42, The ECM just knows that it lost the Reference Pulse from the ICM. You'd really need a 2 channel scope for this to see if the CKP signal dropped out at the same time as the Reference Pulse or not.



The EST system is basically the same EST to ECM circuit used on the distributor type ignition systems with EST. This system includes the following circuits:

• DIS Reference (CKT 430) - The crankshaft sensor generates a signal to the ignition module, which results in a reference pulse being sent to the ECM. The ECM uses this signal to calculate crankshaft position and engine speed for injector pulse width.
• Reference Ground (CKT 453) - This wire is grounded through the module and insures that the ground circuit has no voltage drop between the ignition module and the ECM, which can affect performance.
• Bypass signal (CKT 424) - At approximately 400 rpm, the ECM applies 5 volts to this circuit to switch spark timing control from the DIS module to the ECM. An open or grounded by pass circuit will set a code 42 and result in the engine operating in a back-up ignition timing mode (module timing) at a calculated timing value. This may cause poor performance and reduced fuel economy.
• EST circuit (CKT 423) - The DIS module sends a reference signal to the ECM when the engine is cranking. While the engine is under 400 rpm, the DIS module controls the ignition timing. When the engine speed exceeds 400 rpm, the ECM applies 5 volts to the bypass line to switch the timing to the ECM control (EST). An open or ground in the EST circuit will result in the engine continuing to run, but in a back-up ignition timing mode (module timing mode) at a calculated timing value and the SERVICE ENGINE SOON light will not be on. If the EST fault is still present, the next time the engine is restarted, a code 42 will be set and the engine will operate in the module timing mode. This may cause poor performance and reduced fuel economy.

Thanks Clinebarger for this info. I guess I will have to bring the harness up to where I can inspect it closer. You can't really see most of it from underneath.

I do not have a scope or really the know how to use one correctly.

Is there any way to test the DIS module and coils on this system with a multimeter? In the past I have taken the DIS to the parts store and they had a machine that would test it but they no longer have one so I can't do that anymore.

Given that the last Standard brand DIS and one Coil did not last more than 11,000 miles, I don't have much confidence in this brand.

Once the weather gets better, I will dig into this some more to see if I can determine if there is a wiring issue. Thanks again.