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ICM issue?

4K views 30 replies 5 participants last post by  youjest88 
#1 ·
Hello, I have an 88 I6 4.2 with MC 2100 and HEI.

I'm having an intermittent problem with my jeep stalling without warning while driving and then it'll crank but won't start again until it cools down a bit. I have had the ignition coil replaced, but that didn't fix it. The fuel pump has been replaced within the last year, so that shouldn't be the problem either.

My mechanic is recommending swapping out the ICM, but he says there is a chance that it might not be the problem. They've been driving it around and it hasn't stalled on them, so they can't seem to diagnose the exact issue.

I don't want to just throw parts at it, especially since I am paying for labor. He says it's going to cost me around $300 all said. Anyone have any other ideas?

I hate to be that guy, reporting back to my mechanic what I read on the internet, but I've already emptied every pocket, if you know what I mean.
 
#2 ·
#4 ·
I believe it is mounted on the passenger side inner fender well so it should be easy to get to and a small socket set will unbolt it from the fender well and the plugs have little clips you need to disengage to unplug it. Reverse the procedure to install.
That is the same basic module Ford used in the 80s , my wife had a Ranger that would eat them so I bolted 2 of them on the fender so when one would quit she could plug the other in.
 
#5 ·
Mowrangler is almost correct. It's under the overflow tank on the driver side fender well.You'll have to crawl under to see it.

Easy swap, 4 screws and 2 connectors. I think a module is about $45. Most parts stores can test yours if you take it in, but an intermittent problem may not show up. $300 for that job is robbery.

Another possibility is the pickup in the distributor. They do go bad, and if it's not sending a signal to the ICM it won't fire. Just something to keep in mind.

Edit: I didn't read very well. When you say HEI you mean GM style HEI or Team Rush? If it's a GM type the ICM is in the distributor.
 
#10 ·


12v to power the distributor, yes, but there is an ICM inside.

It is the GM style HEI.

I'll try the ICM swap myself since they're pretty inexpensive. Even if that isn't it, it's one less thing that can fail in the future, right?
It's an easy swap, but one word of advice. Use a quality thermal paste (think computer CPU heat sink) instead of the dielectric grease that comes with the module. It'll last much longer.
 
#12 ·
Crap, looks like I just went and bought the wrong ICM. I was fairly ok with the idea of replacing the "stock" ICM located on the fender wall, but less inclined to take apart the distributor. It looks easy in the video but I know I'll **** it up. Also, if I just got this distributor installed less than a year ago, how is the ICM already messed up? If I replace it, will it fail again in less than a year because some other issue is causing them to die?
 
#13 ·
Firstly, if you can operate a screwdriver you can change the ICM. It is as easy as she made it look.

Since GM has quit producing the modules the quality has gone down. Heat can kill one quickly - as in a bad application of thermal grease. Semiconductors don't like heat.

Could be you have another issue, too. I tend to agree that the ICM is a likely culprit, but check the 12v feed to the dist and make sure those connections are good.
 
#25 ·
Or try this:

Team Rush, which used the stock ICM ...


GM HEI, which uses the 4 pin GM module ...
This is not my jeep, but it looks like this... gray cap:

http://www.jeepz.com/images/howto/tfi/tfi6.jpg

It looks like the module I need is this one:

http://www.summitracing.com/parts/ACC-35368/

I watched a video on youtube of a guy replacing one on an old Ford truck and it looks simple enough, although I didn't entirely understand the part about making sure the distributor is advanced/rotated the correct way or else it would have to have the timing redone.

https://www.youtube.com/watch?v=dAsEiEzKsHE
 
#29 ·
Reporting back. The swap was easier than expected! Unfortunately, it didn't solve the problem. Took it back to the shop and they decided it was the fuel pump after all. Apparently the pump I had installed 18 months ago was a "universal" type and not model/year specific and it crapped out.

So, I guess I'm back on the road for now. Thanks everyone for your help.
 
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