Yo guys, what the heck is going on with my motor. If it's a hot 100+ degree day, and after I've been out driving for a while and everything under the hood is hot as hell, if I stop at a light, the engine will start idling rough, then die. And it won't restart until it cools down. What is causing this? Am I loosing spark? The HEI module in the dizzy can't take the heat? Or is it the ECM keeling over? Help!

 

Whats the motor temp when it dies?

 

I'd say check your ignition module. I've had symptoms exactly like you described, with that being the culprit. "heat soak" of the module tends to be an issue with these cars.

 

About 220 or maybe a little higher. Maybe I need the fans to turn on at lower temps??

 

That's exactly my thinking. I'm thinking that as soon as I stop moving at the traffic light, the underhood temps go through the roof. Particularly if I just pulled off the freeway, and had been driving 70 mph for a good 20 minutes or so. Fans hadn't turned on yet. And there's the module, closed up inside the dizzy, up near the top of the engine bay. Heat soak. A month or so ago, I had a Pertronix hei module crap on me while I was going 65, on a bloody hot day, going uphill. It died permanently, after it cooled, engine still was dead. Swapped in a replacement module and the engine fired right up.

What's with these damn modules? Who makes one that can take California summers? I assume the most reliable is the AC Delco. It better be, at $82 bux.

 

you should be able to get a Delco module for less than $82.00. seems like people have said they are around $40.00 at gm parts direct. be certain you thoroughly clean the dizzy where the module mounts & pick up some good heat sink grease (not dielectric grease, but the white or sliver stuff) & use enough to get a good coat on the bottom of the module.
also, replace your ignition coil when you replace the module, a bad coil will take the module out & its not worth the worry trying to get by with the old coil, use a Delco for it too.

 

Well, that $82 price did come from GM Parts Direct. Maybe the old 4 pin modules go for $40, but the 8 pin versions for the external coil computer controlled dizzys seem to cost a lot more. The local Kragen will also sell them for $82, according to their website. I know a guy back east who is a wrench for a GM dealer. Maybe he can get one cheaper at employee discount and mail it to me.

Cleaning off the bottom of the module and the mounting surface on the dizzy goes without saying. I do have the silver thermal grease, and used it.

The coil is a brand new MSD 8226.

Regardless of all that, the module failed. Again. I am willing to pay the friggin 82 bux if I can get a module that can take the heat and continue to work. Being stuck on the side of the road on a 105 degree day SUX!!! My original module lasted years in there, on hottern'hell days, until it finally failed several months back. And it was not hot when that happened. I only see the problem on the hottest of days, when I get slowed down or stopped, and there is no airflow under the hood.

Jeez, I wish our cars had cowl flaps on the hood like on the old piston airliner engines, and they would open when you were moving at less than 20 mph and the engine temp went over 220. That would let all that trapped hot air escape.

 

Vapor lock?

 

Can TPI vapor lock? I would think that 40+ pounds of fuel pressure in the rails would prevent that.

 

i have never heard of any fuel injected car vapor locking. i don't think its possible with TPI.

if you had an aftermarket module that could well be the reason it didn't last.
i will not sell aftermarket modules or ignition coils, a lot of customers complain about the price but i refuse to have the headaches that go with using those parts.

im not sure any of the aftermarket ignition coils will fire hotter than what a good Delco coil will. the way i test the external HEI coils is by pulling the coil wire off of it & then crank it over. if its good i can hear it fire down the tower to the laminations. they fire that hot.

 

Well, just to make sure, I pulled the module and cleaned the hell out of it, made sure there was no dirt or anything on the baseplate, and noticed that there was a thin film of what looked like oxidation or light corrosion on the baseplate. I cleaned that off to shiny metal. I also cleaned the electrical connectors. Also cleaned the mounting surface in the dizzy. When everything was totally clean, I put on a fresh layer of the silver thermal compound and re-mounted the module, and snugged it down nice and tight.

Let's see if it happens again.

I see I can get a genuine AC Delco module from Rockauto for 50 bux plus shipping. That's the cheapest I've seen them, even cheaper than GM Parts Direct.

Interesting way to test a coil! the only concern I would have with your method is if it might cause a carbon track down the tower to the lams. That would be bad news. I understand your reluctance to sell anything other than genuine Delco parts, but OTOH, I think MSD makes a good solid product.

 

if the coil wire doesn't have a good seal around the tower & you have a bad plug wire you can get carbon tracking over time, but when i find a open plug wire i always replace the coil anyway because in those cases the coil has been stressed hard & i have no ideal for how long so i don't trust them at that point.

doing this to test the coil does put a lot of stress on it which is what i want, but it should be able to handle it just fine, if the coil can't take a few seconds of it then the coil needed to be replaced anyway.

if i didn't replace a coil that is weak or may fail soon, i feel like i would have let my customers down.

 

My friend who is a wrench for a GM dealer says these thick film circuit modules have known problems when they get really hot. High heat will kill them and failures from overheat is not uncommon. In fact, he said Ford used a similar unit and it was so unreliable, they had a class action lawsuit brought against them.

So, given that they are sensitive to heat, it is important to make damn sure it is mounted properly, and that means the mounting surface on both the module and dizzy must be totally clean, no dirt or grit or anything whatsoever. Then, a film of proper heatsink grease is applied to the bottom of the module, and it is then snugged down firmly. It also means, that if you have to replace yours, do NOT buy a cheapie lo buck house-brand replacement. Buy genuine Delco. RockAuto has them cheaper than anywhere else. You can get a discount code from the Ford forums and get a few bux more off the price.