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LT1-LT4 Modifications
1993-97 Gen II Small Block V8

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Old 11-20-2009, 07:06 PM   #1
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Default What are the symptoms of a bad Ignition Control Module?

What does it usually do when it goes bad? Does it just die and the car will not fire, period? Does it sometimes give an intermittent signal and the car will run sometimes fine, weak other times, and not at all when it is being extra ornery? Any chance of it spitting and farting running like pooh until it decides to run right and then its fine until it does it again...usually hot? Or is all this more likely opti?

Basically, the car has had this issue more off than on for a few months now, but the last week it has been more often than not and tonight I barely made it home. When it misbehaved, it spit and fart would barely idle, if at all, and then when it sat for a bit or after some more tries and about 5-10 minutes it would fire again and seem to run alright for a while until it did it again...got hot again. When it does it you can smell unburnt fuel as well which is why I condemn something in the ignition...plus I replaced the fuel pump with a Walbro very recently and while it is not impossible to be fuel pump, it just doesn't act like a fuel issue.

Any help would be appreciated ASAP as I am trying to get this running by Monday again and buy my parts this weekend...unless of course it's an opti, then I may have to order online and wait as I really don't want to waste my time with anything but a Delco unit. Thanks everyone.
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Old 11-20-2009, 09:43 PM   #2
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When mine failed, I was driving down the road and the engine quit. No miss, no stumble,, nothing, engine just QUIT.

Pulled over and cranking didn't re-start it. I sat for several minutes planning my next move then decided to try it again and the engine fired like nothing had happened.

I then drove a couple of more miles and the engine quit again. Same thing, wouldn't re-start until car sat for several minutes, then it would.

I suspect it was heat related. After going through that five or six times I finally made it home. New ICM next day and I never had that problem again.

When checking the bad one during the swap I saw that there was still a good amount of silicone grease on the mounting side of the ICM. So absence of grease wasn't the cause.

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Old 11-21-2009, 06:43 AM   #3
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I was initially thinking ICM, but then the spitting and farting thing and running like crap in between the no run and running fine threw me off. I think I will do the ICM and see what that does...it's easier for one and cheaper. I did the cooling mod, but it already had 116K on the clock, so the damage could already have been done. Thanks for the reply.
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Old 11-21-2009, 08:11 PM   #4
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Alright, well I may have fixed this problem...we'll see as I drive the car over the next few days, but it fired right up and seems ok for now tonight. Turns out I am a dumb ***. I replaced the fuel pump and the relay was working ok then and up until this last week I could hear it priming every time I went to start and just took it for granted. Well, after messing with it a few times I noticed the pump didn't seem to be priming and at first thought maybe it was because the car had been running that night and had rail pressure or something...but after a while when going to crank it again I noticed it still didn't prime. Fiddled with the relay and jumpered it...fired right off. Replaced the relay and all seems ok for now. Might have been an intermittent issue for a while and never really noticed with the pump having been replaced recently and usually hearing the pump prime. Anyway, just thought I would share.

This is just proof to everyone in doubt or just starting off in turning wrenches that it pays to 1) have a fuel pressure gauge handy...which I didn't because it lives at my shop, and 2) always test/check for the first/basic things or symptoms no matter what you have replaced recently or assume is ok...it could be an easy fix.
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Old 11-23-2009, 01:07 PM   #5
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Quote:
Originally Posted by creepingdeath94 View Post
I was initially thinking ICM, but then the spitting and farting thing and running like crap in between the no run and running fine threw me off. I think I will do the ICM and see what that does...it's easier for one and cheaper. I did the cooling mod, but it already had 116K on the clock, so the damage could already have been done. Thanks for the reply.
cooling mod? what damage are you talkng about? this could also be caused by the throttle position sensor which is what happened to me
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Old 11-23-2009, 02:02 PM   #6
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Usally just quits. Sometimes the will misfire, and/or backfire through the TB or Carb. I had one on an 86 Model Chevrolet truck back in the spring that would fire good with a plug out, Modual checked good, 3 times, but would not hit for ****. Turned out it was a bad igntion Modual
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Old 11-23-2009, 02:34 PM   #7
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cooling mod?
Some people put some washers, or some other type of spacer, behind the ICM to move it away from the head.
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Old 11-23-2009, 03:37 PM   #8
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So far so good. Drove it to temp. last night again and into work, out for lunch, and hopefully home here in a couple hours and so far no issues. I think it was just a failing fuel pump relay that finally got bad enough it was inoperable more often than operable. Anyway, I will consider this "problem solved" unless it happens again here in the next week or so. Thanks again for all the replies.
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Old 11-23-2009, 03:37 PM
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