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1997 Grumman Olson 12 ft step van, NA 6.5 diesel (RPO L57), 4L80E transmission
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That's a pretty specific alloy to be using to make a cosmetic cover, wouldn't you think? Considering the environment where this device is designed to work, in the hot valley of a V-8, I'd bet those thermalloy covers over the power transistors are there to shield them from external heat by shunting that heat around the cases of those transistors to the heat sink to be cooled by incoming fuel. The idea would be to limit the heat the transistors must endure to the heat they generate themselves while operating.

I think.
 

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1997 Grumman Olson 12 ft step van, NA 6.5 diesel (RPO L57), 4L80E transmission
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41 Posts
I remember reading some detailed failure analyses of these drivers, and it isn't thermal runaway that's killing these PMD's. It's the stiff epoxy the manufacturer used when they potted those modules. The epoxy has different thermal expansion properties than the leads of those big power transistors. Every time the unit heat cycles with engine operations, those transistor leads tug a bit on the circuit trace pads to which they are soldered. Enough of that cyclical stress cracks the solder loose at the circuit board, creating a high resistance or intermittent connection, making your injection pump's fuel servo behave erratically.

I'm sure Stanadyne must know this, but there sure seems to be a lot of these modules failing.

I was relieved to learn I had the DB2 pump on my 6.5! But, on the other hand, the solution to a fueling problem I'm having isn't immediately obvious
That's a pretty specific alloy to be using to make a cosmetic cover, wouldn't you think? Considering the environment where this device is designed to work, in the hot valley of a V-8, I'd bet those thermalloy covers over the power transistors are there to shield them from external heat by shunting that heat around the cases of those transistors to the heat sink to be cooled by incoming fuel. The idea would be to limit the heat the transistors must endure to the heat they generate themselves while operating.

I think.
I think I have it backwards. It just dawned on me the photo is of the machined plate that gets the thermal paste and then bolted to the side of the injector pump.

It's hard to tell in the photo. Are the tops of those covers level with the heatsink? Do those thermalloy covers get thermally coupled to the injector pump with thermal paste as well? If so, they would hugely help cool those power transistors by conducting some more of their heat away with those covers instead of those transistors radiating it away.
 
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