4th Gen 93 LT1 Camaro ICM Trouble

[Pranav]

http://ls1tech.com/forums/lt1-lt4-mo...need-help.html

[Fbody383]

We replaced the computer and the chip in the computer. Still thinking we should have let it burn...

The ICM triggers the coil - is the primary coil winding bad under heat/load so that it's grounding out the ICM?

Are you comfortable that you know what's killing the ICM? Heat? Current? Other?

[Sook]

Factory wiring harness was replaced with a Howell EFI engine harness.
http://howellefi.com/general-motors/...e-1993-camaro/

Swapped the alternator wiring around to Pranav style, car is charging, DC bus is still a bit noisy, and I'm still getting erratic tach. No idea if it's better or worse. One thing I do notice is that it looks like the alternator is kicking on and off, going between 12 and 14 volts occasionally. Usually always 14, but it dips for seconds at a time. I guess S is a sense line, looping back to the alternator output. Not having to futz with a resistor is nice.

The coil has been swapped twice, the one that was on the car when I initially tried to start it seemed to have a damaged connector. The second on was swapped when trying to diagnose the initial ICM failure. Third one still on the car.

I'm not comfortable saying the sky is blue, much less what's killing the ICM. I'll probably do a cooling mod as well - still no smoking gun on what's killing them.

- Josh

[GlennCMC70]

Make sure you are using thermal paste under the icm and not dielectric grease.

[Pranav]

Is it possible that one of the ICM wires are reversed? I've heard of painless harnesses with a random wire being swapped by mistake...

[Supercharged111]

Factory wiring harness was replaced with a Howell EFI engine harness.
http://howellefi.com/general-motors/...e-1993-camaro/

Swapped the alternator wiring around to Pranav style, car is charging, DC bus is still a bit noisy, and I'm still getting erratic tach. No idea if it's better or worse. One thing I do notice is that it looks like the alternator is kicking on and off, going between 12 and 14 volts occasionally. Usually always 14, but it dips for seconds at a time. I guess S is a sense line, looping back to the alternator output. Not having to futz with a resistor is nice.

The coil has been swapped twice, the one that was on the car when I initially tried to start it seemed to have a damaged connector. The second on was swapped when trying to diagnose the initial ICM failure. Third one still on the car.

I'm not comfortable saying the sky is blue, much less what's killing the ICM. I'll probably do a cooling mod as well - still no smoking gun on what's killing them.

- Josh

Cooling mod schmooling mod. I've been doing this since 2013 and haven't smoked an ICM though I did deal with extensive knock sensor issues. I have smoked an ICM on an older truck so I'm not invincible. Point is, the ICM itself is not such a POS. The factory puts out parts that work, you just need to figure out what's screwing you over and don't rule out those garbage ass Autozone parts.

[Sook]

Running thermal grease, even got some fancy stuff by the time I got to the 3rd ICM.

I checked the ICM wires per shbox's diagrams, but who knows - won't hurt to check them again.

Here's a video of the tach:
https://drive.google.com/open?id=0B_...kpNbTdsTWc3N1k

I let the car idle in the garage for about an hour with a new ICM and alternator. Over that time the tach 'jumpiness' got worse. Alternator voltage dropped from 14.5 to 13.5 on average. Now I'm suspecting the opti/plug wires. Maybe high voltage leakage is escaping to ground some where and polluting the system and damaging solid state electronics. I'll try to get a hold of a set of wires (I'm on a first name basis with all the local car part shops lately...) and see if that makes a difference.

Thanks for all the responses, hopefully I'll get to the bottom of this soon. I'll report back with results!

- Josh

[Fbody383]

Is it possible that one of the ICM wires are reversed? I've heard of painless harnesses with a random wire being swapped by mistake...

Like power/ground on the windshield wiper motor on a 69 Camaro harness... Good news is if you take the entire harness back out they'll warranty the harness.

[Storm Trooper]

Running thermal grease, even got some fancy stuff by the time I got to the 3rd ICM.

I checked the ICM wires per shbox's diagrams, but who knows - won't hurt to check them again.

Here's a video of the tach:
https://drive.google.com/open?id=0B_...kpNbTdsTWc3N1k

I let the car idle in the garage for about an hour with a new ICM and alternator. Over that time the tach 'jumpiness' got worse. Alternator voltage dropped from 14.5 to 13.5 on average. Now I'm suspecting the opti/plug wires. Maybe high voltage leakage is escaping to ground some where and polluting the system and damaging solid state electronics. I'll try to get a hold of a set of wires (I'm on a first name basis with all the local car part shops lately...) and see if that makes a difference.

Thanks for all the responses, hopefully I'll get to the bottom of this soon. I'll report back with results!

- Josh

It looks like a ground issue to me. I bet you're pulling the ground through your ICM. Make sure your batterie to the chassis ground your chassis ground to the block. Also check your harness from Howell, I use the same harness. make sure you have a good ground attached to the back of the aluminum head. Measure the resistance from ground to the ground wire on the ICM. Make sure you have a good ground. Did I say check your ground? :-)

[Storm Trooper]

Factory wiring harness was replaced with a Howell EFI engine harness.
http://howellefi.com/general-motors/...e-1993-camaro/

Swapped the alternator wiring around to Pranav style, car is charging, DC bus is still a bit noisy, and I'm still getting erratic tach. No idea if it's better or worse. One thing I do notice is that it looks like the alternator is kicking on and off, going between 12 and 14 volts occasionally. Usually always 14, but it dips for seconds at a time. I guess S is a sense line, looping back to the alternator output. Not having to futz with a resistor is nice.

The coil has been swapped twice, the one that was on the car when I initially tried to start it seemed to have a damaged connector. The second on was swapped when trying to diagnose the initial ICM failure. Third one still on the car.

I'm not comfortable saying the sky is blue, much less what's killing the ICM. I'll probably do a cooling mod as well - still no smoking gun on what's killing them.

- Josh

With the 470 ohm resister between your sense and your sorce. Your alternator should put out steady it should not fluctuate. Also if you have a bad ground your alternator will not put out correctly. Did I say check your ground? :-)