Camaro Z28 1991 with 350 TPI engine. I’m having some problem here with the spark advance. As stated in the title, I’m loosing the spark advance after running the car for a few minutes. So, I’m stuck then on the base 6-degree BTDC. Just like if I would pull apart the EST connector. To get the spark advance to work again I need to disconnect the battery for a minute or two. Then everything is fine again for a while.

 

A few days ago, I went and got a guy to read the fault codes since the “Service engine soon” light is on.

14 Coolant temperature signal low or shorted

45 Rich exhaust

42 Electronic spark timing (EST) problem.

I have changed the temp sensor and even measured the cables all the way to the ECU. Still have the same problems, engine runs fine for maybe three minutes, and then goes in to what I believe is “limp home mode”. No spark advance, and electric fan goes on even though engine is far from hot. I would think code 45 and 42 is caused by running in “limp home mode”.

Anyone have an idea what this could be?

 

Code 14 is cts reading high or shorted, what does the cts ohm at the cts and at ecm ?
does a scanner match cts ohm to temperature reading at E16 of the ecm ?

 

Now I'am down to only one code.
42 Electronic spark timing (EST) problem.
Engine runs fine for a few minutes and then service light comes on. I will try to go through the flowchart for code 42.

 

I got the ICM pointed out in the flowchart, had an old one. Put that one in and code 42 is gone, I will need to drive around some more to be sure though.
This is my third ICM that breaks in three yeras, this can't be right? The last one was a GM original. What brand is best, I like to have one I can trust.

 

If some thermal paste helps dissipate the heat that kills it...maybe more is better??? Or time to get creative and employ some sort of heat sink to make it live a happy life...
https://www.thirdgen.org/forums/v6/1...ml#post1143351

 

After driving around for a while the bottom of the distributor (opposite the ICU) is so hot that you burn your fingers on it. So That ICU sure have to stand a lot of heat. I don't think a small heat-sink will make much difference. But maybe a liquid processor cooler like this one can do the job if it will stand the heat.

Processor cooler

 

A couple of thoughts here, in no particular order;

First off, forget the "more is better" ethos, actually more is worse, the thicker the layer of thermal paste, the further apart are the ICM and the distributor body.

Thing brings us to the "better is better" ethos, , , the stuff that comes with a replacement ICM is garbage, I use this product instead;

https://www.arcticsilver.com/as5.htm

Another thought, I know of no other car in this forum that requires a liquid cooled heatsink to keep the ICM from frying. If your ICM frying don't stop by using a proper amount of decent quality thermal paste like I linked above, my next question would be what kind of ignition coil are you running? A stock style one or one of those aftermarket "blaster" type?

 

I'm using what supposed to be a good paste for computers. Arctic MX-4 thermal compound.
Yes about the coil, its a MSD 8226, could that be the problem?

 

In my opinion, yes.

With your new ICM, try a stock type coil and see how long the ICM lasts

 

Thanks, I will go all stock as next step and see how that works.

 

I have read at least a few threads here where people had problems with aftermarket coils frying ICMs, and I have also read that the stock ignition system is not the "weak link" in making power till your looking for over around 500HP .

 

I think I have finally solved the problem. It was the ECU all the time. Intermittent problem that sometimes showed up several times a day, and then went away for a week. Was making me crazy before I changed the unit a month ago.