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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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Discussion Starter #1
A while back I posted some questions about my 1992 Fleetwood. She wasn't running right, and still isn't 100%, but she ran MUCH better today after I worked on her.

In the last few months, I have replaced the air filter, fuel filter, spark plug wires, distributor cap, rotor button, and pcv valve on my car. However, instead of running better, she started developing issues. For the last month or longer, she has had a noticeable misfire when coasting in the 30-50 mph range, with the worst symptoms right around 45 mph.

A friend with considerable mechanic experience (he has rebuilt more motors than I have owned) thought it was the ignition coil, so that was the last thing I replaced. The exact same symptoms persisted. So I felt like my best bet would be to remove the ignition control module and test it, and I did that today after work. I tested it 12 times so it would get ridiculously hot. I'm surprised it wasn't glowing red, because that little booger was HOT!

Passed. Passed. Passed. Passed every damn time. So I reinstalled it, applying a healthy amount of grease to the back of the module, and checked every bolt in the distributor that I could see to make sure they were tight. None of them tightened any, so they were all good.

Crank the car, let it run, drive it, get it hot (that's when the symptoms start - at operating temperature.)

The car runs great all of the sudden!!!

Could it just have been that removing, re-greasing, and reinstalling the ICM straightened out the problem? And will it still run good tomorrow? :suspect:
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
It is possible that it was a less than perfect electrical connection. I think it's safe to say that the ICM is good. Let us know what happens tomorrow.
 

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1985 Sedan DeVille
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1,883 Posts
Stumble at cruise is pretty typical symptom for ICM failure

Might have just needed a fresh dose of heat compound
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #4
When I removed the ICM, it had almost no compound on it. It was barely detectable.
 

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1991 Cadillac Sedan deVille
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591 Posts
Having very little/dried out heat-sink compound/grease will be causing it to overheat and fail prematurely. It might have been the improved heat dissipation or the reseated electrical connections. Hopefully that was it and it runs just as good tomorrow and the next day, and the next… :)
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #6
I would have responded yesterday but my computer monitor died, and I don't have a smartphone or tablet. I'm sort of a technology dinosaur, just waiting for an asteroid to crash into my planet and wipe me out.

The car ran better for a little while, and went back to it's old ways. HOWEVER, I used standard dielectric grease to insulate the ignition module, not the proper stuff, because I couldn't find the proper stuff at the time. I have since then found the proper grease, so I'm going to take it apart for the 3,000th time and do it right. The general opinion is that the standard dielectric grease will work, but I'm not so sure. Putting a substance on there seemed to help at first, but I think the proper stuff would do better. So we'll see, as soon as I can get around to it.
 

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1985 Sedan DeVille
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1,883 Posts
you might try some CPU heatsink compound, very very high thermal conduction on that stuff, and its pretty cheap
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #8
you might try some CPU heatsink compound, very very high thermal conduction on that stuff, and its pretty cheap
That's what I'm going to have to do I think. Turns out the product I bought, even though it specifically says on the package that it is factory spec for using on a GM ignition module's backside prior to installation, it is NOT that product. It is just a big old tube of standard dielectric grease. I'm gonna keep it though - I'll need it for something eventually. Trying to find the heatsink compound locally.
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #9
So I finally got some CPU heat sink compound today! Basically the same thing as Arctic Silver and others like it. I applied the compound, but it didn't help any. So I tried to think of anything I may have missed in the past, rechecked a few things, and realized I had gotten a false positive on doing a "stethoscope" test on the injectors. Cylinder 5 isn't opening and closing like the others. There is a nice, audible "CLICK CLICK CLICK..." coming from the other injectors, and really no sound at all coming from #5. I'm going to get my friend's multimeter, check them all, and then take said multimeter to the pick-n-pull yard and get myself a handful of good ones. I'm going to replace any that fall below spec, and have another couple on hand for next time.

To paraphrase Avril Lavigne:

Why do you have to go and make things so complicated?
I see the way you're
running like you're some other car, gets me frustrated.

*drops mic, walks off stage*
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #11
It's been weeks since I decided to buy my fuel injector, and I just haven't had time to mess with it. I told my good friend Eric, the mechanically experienced person I mentioned in post #1 of this thread, about the problem. He knows how busy I am working two jobs, and decided to surprise me tonight by showing up with all his tools, ready to work. Eric is about 65 and had already worked on his pickup all day, but knew I needed the help.

He got me out the door by saying "Well, it won't hurt to look at it." An hour later we had injector #5 replaced, and were back from the test drive. I think my ISC needs cleaned and adjusted because the idle still isn't ideal, but the bucking and stutter at low RPMs is gone! She runs and feels SOOOOOO much better, shifts feel better, the whole works! It took a few minutes of driving it for it to level out, I suppose because of old crud in the system, crud we loosened and made it's way into the engine, etc. You guys may never meet Eric, but I am very greatful to have friends like him in my life! And friends like you guys, with lots of great suggestions and advice!
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #13
The throttle body is clean-ish. I need a good brush to really go over it with. But it isn't bad dirty, just a little.
 

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1992 DeVille
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2,339 Posts
ratmonster said:
The throttle body is clean-ish. I need a good brush to really go over it with. But it isn't bad dirty, just a little.
That might smooth your idle out a good amount. I thought mine was clean but I went over it a week or so ago and it made a world of a difference =)

You just replaced the one injector?!
 

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1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Discussion Starter #15
Yup. Only cost me $15 dollars. I'm hoping to do them all with the improved units available online. But that'll have to wait until I have the money. It'll cost $100 - $200 for the set, and I just don't have that kind of money right now. Maybe at tax return time.
 
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