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Black plastic caps on PMD

I don't think the stanadine bean counters put these caps there to make it look pretty or to spend money.
There must be a reason for them to be there me thinks
 
The OEM PMD I took off the IP had the plastic caps on it. So I mounted the new one with plastic caps in the bumper. So far so good 14 mos. later.
 
IIRC there was a GM or a stanadyne memo to remove them, you know the same 2 entities that decided the on IP FSD location was okay, I removed mine before going with the Heath setup which seems/d to assist in keeping them cooler.
 
Hi Gunar,

Here's what I posted on the other Place:

"Hi XXXXXXXX,

I did some research a while back on the Stanadyne PMD/FSD, the circuitry design is guarded better than our nuclear weapons technology.

The module dissipates heat proportional to the solenoid drive signal pulse width. In other words the more fuel commanded from the IP, the hotter that little module gets.

For it to operate in a normal thermal range (outside of the engine bay) it needs adequate heatsink capacity and a low thermal junction to said heatsink. The Stanadyne included film/sheet type thermal pad looks to be a composite or poly-plastic substrate with a sprayed on thermally conductive dark gray powder.

Looking at the back of the PMD module you’ll probably see two recessed black plastic caps. These are electrical insulators for the module’s output stage metal canned Bipolar Transistors. The Transistors case is electrically charged positive, and if allowed to short out to chassis ground via the heatsink, bad things happen!

Arctic Silver5, per the MFG it contains “With its unique high-density filling of micronized silver and enhanced thermally conductive ceramic particles”.

Yep that’s right it’s electrically conductive, and care should be used even when using it on computer CPU’s. Now if that stuff contacts the Transistors metal cans (Base) and a chassis grounded heatsink ~ well I think you can guess the out come! All kinds of weird IP/ECM/PCM behavior, not to mention premature failure of the module!

I used a different compound from the same MFG, it’s called Céramique and is actually now Céramique version 2. It’s NON-electrically conductive and safe for the PMD, plus it coefficient of thermal transfer is almost as good as the AS5, and is much better than the common grades of silicone based thermal compounds.

Anyway, food for thought?"
---------

Come to think of it, I never tested the Stanadyne (Dtech, Flight) included film thermal pad for surface resistance. If it’s even semi conductive and it touches the Transistors metal can (Base) and a chassis grounded heatsink, because the owner removed the black plastic caps before mounting the module?

WOW, might I have just stumbled upon an ever-elusive cause of IP error codes, bad drivability, prematurely failing PMD/FSD?:eek:

And I’d keep those caps also, to reinstall upon module failure. Most companies don’t appreciate (honor warranties) if they think the customer has adulterated their product.


Note: I don’t officially endorse or recommend the following to anyone!
I personally removed my black caps, and placed them in the round-file ~ after thought ~ I should of kept those:mad2:. But I also stuck the wrinkled up included thermal film pad in the round-file. I mounted mine with non-conductive thermal compound, and actually filled the Transistor cavities with it. Those TO3 metal canned Transistors can only transfer so much heat from their mounting interface. By encapsulating them they’ll be able xfer a bit more heat to the heatsink.

Chris
 
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