1994 ICM Blues
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
1994 ICM Blues
Working on the wifes 94,
The car has had a running rough problem for the last couple of months
OptiSpark was replaced with a Petris unit, waterpump, coil, plugs and wires were all replaced. The car ran perfectly smooth for a month then got rough again. Decided I would replace the ICM, Well so far I've put in 3 different brand ICM's from different places and each time I put a new one in the service engine light comes on. Pull the code and its a shorted ICM. I put the old one back in and the code goes away.
Is it that the ICM's are actually bad or something else? I can't believe that all 3 that are different brands would all be bad.
The car has had a running rough problem for the last couple of months
OptiSpark was replaced with a Petris unit, waterpump, coil, plugs and wires were all replaced. The car ran perfectly smooth for a month then got rough again. Decided I would replace the ICM, Well so far I've put in 3 different brand ICM's from different places and each time I put a new one in the service engine light comes on. Pull the code and its a shorted ICM. I put the old one back in and the code goes away.
Is it that the ICM's are actually bad or something else? I can't believe that all 3 that are different brands would all be bad.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
are ANY of these the OEM brand?
I'm not familiar with the misc Opti pieces and who makes them, but I KNOW that the HEI likes delco and will often malfunction with the "store brand" or the cheaper option. I had that happen with the ICM in the HEI dist...random misfire, poor advance, overall poor performance. Someone suggested the ICM and I got the GM delco version and solved all the problems.
I was told that its got to do with the calibration of the ICM. Some are generic to fit other applications reducing production cost, while the GM/Chev part is made specifically for the yr, make and model. The proof is in the price !
I'm not familiar with the misc Opti pieces and who makes them, but I KNOW that the HEI likes delco and will often malfunction with the "store brand" or the cheaper option. I had that happen with the ICM in the HEI dist...random misfire, poor advance, overall poor performance. Someone suggested the ICM and I got the GM delco version and solved all the problems.
I was told that its got to do with the calibration of the ICM. Some are generic to fit other applications reducing production cost, while the GM/Chev part is made specifically for the yr, make and model. The proof is in the price !
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
are ANY of these the OEM brand?
I'm not familiar with the misc Opti pieces and who makes them, but I KNOW that the HEI likes delco and will often malfunction with the "store brand" or the cheaper option. I had that happen with the ICM in the HEI dist...random misfire, poor advance, overall poor performance. Someone suggested the ICM and I got the GM delco version and solved all the problems.
I was told that its got to do with the calibration of the ICM. Some are generic to fit other applications reducing production cost, while the GM/Chev part is made specifically for the yr, make and model. The proof is in the price !
I'm not familiar with the misc Opti pieces and who makes them, but I KNOW that the HEI likes delco and will often malfunction with the "store brand" or the cheaper option. I had that happen with the ICM in the HEI dist...random misfire, poor advance, overall poor performance. Someone suggested the ICM and I got the GM delco version and solved all the problems.
I was told that its got to do with the calibration of the ICM. Some are generic to fit other applications reducing production cost, while the GM/Chev part is made specifically for the yr, make and model. The proof is in the price !
My assumption is this is a ignition issue since all injectors OHM out at 12, FPR is 43 static and 38 when at idle. Took a vac reading and thats 18hg at idle.
Drifting
Joined: Mar 2012
Posts: 1,492
Likes: 61
From: New Jersey
Did you clean off the old heat sink paste (also called heat sink compound) on the original icm and put new paste on? You should put heat sink paste on the back of the new icm(s) when you installed them? Also heat sink paste should go between the coil bracket and the head; between the heat sink and the coil bracket; and between the heat sink and the icm. If you haven't done this, try it before replacing the icm as they are quick to overheat (and later burn out) when the paste gets old. I recently did mine and found the old paste had dried out and there wasn't much left on the coil bracket, heat sink and icm.
Good luck!
Good luck!
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
Did you clean off the old heat sink paste (also called heat sink compound) on the original icm and put new paste on? You should put heat sink paste on the back of the new icm(s) when you installed them? Also heat sink paste should go between the coil bracket and the head; between the heat sink and the coil bracket; and between the heat sink and the icm. If you haven't done this, try it before replacing the icm as they are quick to overheat (and later burn out) when the paste gets old. I recently did mine and found the old paste had dried out and there wasn't much left on the coil bracket, heat sink and icm.
Good luck!
Good luck!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
are ANY of these the OEM brand?
I'm not familiar with the misc Opti pieces and who makes them, but I KNOW that the HEI likes delco and will often malfunction with the "store brand" or the cheaper option. I had that happen with the ICM in the HEI dist...random misfire, poor advance, overall poor performance. Someone suggested the ICM and I got the GM delco version and solved all the problems.
I was told that its got to do with the calibration of the ICM. Some are generic to fit other applications reducing production cost, while the GM/Chev part is made specifically for the yr, make and model. The proof is in the price !
I'm not familiar with the misc Opti pieces and who makes them, but I KNOW that the HEI likes delco and will often malfunction with the "store brand" or the cheaper option. I had that happen with the ICM in the HEI dist...random misfire, poor advance, overall poor performance. Someone suggested the ICM and I got the GM delco version and solved all the problems.
I was told that its got to do with the calibration of the ICM. Some are generic to fit other applications reducing production cost, while the GM/Chev part is made specifically for the yr, make and model. The proof is in the price !
Get an OEM ICM as a first step. Mostly likely you're be fixed but if it is not, at least the troubleshooting will be done with the correct parts in it.
Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
Working on the wifes 94,
The car has had a running rough problem for the last couple of months
OptiSpark was replaced with a Petris unit, waterpump, coil, plugs and wires were all replaced. The car ran perfectly smooth for a month then got rough again. Decided I would replace the ICM, Well so far I've put in 3 different brand ICM's from different places and each time I put a new one in the service engine light comes on. Pull the code and its a shorted ICM. I put the old one back in and the code goes away.
Is it that the ICM's are actually bad or something else? I can't believe that all 3 that are different brands would all be bad.
The car has had a running rough problem for the last couple of months
OptiSpark was replaced with a Petris unit, waterpump, coil, plugs and wires were all replaced. The car ran perfectly smooth for a month then got rough again. Decided I would replace the ICM, Well so far I've put in 3 different brand ICM's from different places and each time I put a new one in the service engine light comes on. Pull the code and its a shorted ICM. I put the old one back in and the code goes away.
Is it that the ICM's are actually bad or something else? I can't believe that all 3 that are different brands would all be bad.
I'm chasing a no-start situation on my 94 LT1 which looks like it is my ICM, so was reading your issue and would offer the following thoughts:
1. Is the 'code' you pulled a DTC 42 (IC circuit shorted or grounded? Oddly, per FSM, that code will NOT turn on the MIL (service engine light), so are you also receiving other DTCs? If so, advise, it might help me and me help you...
2. Per FSM, The DTC 42 sets when "the PCM detects 84 crankshaft revolutions without any IC activity" -- interpreting this with it being 'shorted or grounded' -- implies that the normal 0.5-4.5 vAC on the 'B' Ignition Control Module connector (per molded in letters on connector not scematic) is staying at zero --- which would imply either the aftermarket ICs are really bad, or more likely their connections are in a different position than the OEM unit and possibly incorrectly connecting 'B' to the aftermarket ICM's ground connection.
3. Presuming you have the FSM, might want to analyze the AC power feed on the 'B' connector feed to the ICM to see if it is the correct 0.5 -> 4.5 vAC -- warning -- following the diagnosis chart C4 in book 2 section 6E3-C4-5 -- note on the protection procedure to disconnect the 'tach' feed by removing the coil gray connector and jumpering the 'b' ppwer feed.
This vAC feed is the PCM's response to the Distributor's 'pulse' on the low and high resolution circuits -- if it is not bouncing around within the specificed range, it could imply the distributor is the problem and not the ICM.
Last edited by theadmiral94; Oct 15, 2012 at 11:08 PM.
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5th Gear
Joined: Oct 2012
Posts: 5
Likes: 0
I have had ICM issues for years pulling the code 42 . I got a couple ICM's in the back capartment incase one gets wacky and now forget which brand I have in there now. I do not get the check engine code anymore or the no start issues. BUT I have a back up plan for anyone with ICM issues till someone finds a fix for us.
Take a can of keyboard cleaner and keep it in the car for the no start issues. When the car wont start, take the can and turn it upside down and spray it on the ICM. It cools it off super quick, then go start the car ! I used this method till I found a decent ICM. I am too lazy to trace a ground or bad terminal.
Take a can of keyboard cleaner and keep it in the car for the no start issues. When the car wont start, take the can and turn it upside down and spray it on the ICM. It cools it off super quick, then go start the car ! I used this method till I found a decent ICM. I am too lazy to trace a ground or bad terminal.
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
I'm chasing more of a "rough running condition". Prior to replacing the ICM, it had two codes, H65,H83.. these had never turned on the ses light. The ses light would only turn on when I tried a new ICM. Everytime I would go back to the orginal ICM the ses light would turn off. Unfortunetly I don't have a FSM.
Now, I did contact Chris at Petris today to discuss my problem. He made the following suggestions. Before replacing the O2 sensors, to clean out the EGR since its common to have them carbon up and to clean all the electrical connectors for MAF,TPS,etc. I then cleared the codes. Right now I'm back to the orginal ICM until the AC Delco one arrives. My wife will drive it tomorrow and when she gets home I will read it to see if any codes have come back.
Interesting enough he had told me a story where he had a 94 with a no start problem that they were chasing for a long time. He told me that he eventually learned that that were two ICM used and only one of them was the correct one. Once he used the correct ICM it fired up. Unfortunetly with all the information he was giving me I had forgotten to ask about how to know which is the correct one. So you may want to keep that in mind while troubleshooting yours.
Now, I did contact Chris at Petris today to discuss my problem. He made the following suggestions. Before replacing the O2 sensors, to clean out the EGR since its common to have them carbon up and to clean all the electrical connectors for MAF,TPS,etc. I then cleared the codes. Right now I'm back to the orginal ICM until the AC Delco one arrives. My wife will drive it tomorrow and when she gets home I will read it to see if any codes have come back.
Interesting enough he had told me a story where he had a 94 with a no start problem that they were chasing for a long time. He told me that he eventually learned that that were two ICM used and only one of them was the correct one. Once he used the correct ICM it fired up. Unfortunetly with all the information he was giving me I had forgotten to ask about how to know which is the correct one. So you may want to keep that in mind while troubleshooting yours.
Drifting
Joined: Mar 2012
Posts: 1,492
Likes: 61
From: New Jersey
It's probably just a typo on your part but you don't use dialectric grease between the icm, heat sink, and coil bracket. You use heat sink paste made specifically to draw heat away from the icm into the heat sink.
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
you are correct, I got typing to fast. It was the paste that comes with the ICM..
Thread Starter
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
UPDATE
Got in the new AC Delco ICM today from Rock Auto ($78), installed it an this time no SES light. Car seems to be running better. Tomorrow I'll get the 2 exhaust leaks fixed on the eliminators and then I should notice a big differance in performance.
Of course in the process of doing the exhaust repair the wife wants me to make it louder for her!..
Got in the new AC Delco ICM today from Rock Auto ($78), installed it an this time no SES light. Car seems to be running better. Tomorrow I'll get the 2 exhaust leaks fixed on the eliminators and then I should notice a big differance in performance.
Of course in the process of doing the exhaust repair the wife wants me to make it louder for her!..