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looking for used dead 6.5 PMD's

dbrannon79

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Hey Guys, I'm looking around for a couple used and or dead PMD's from a 6.5 gm diesel. I've been wanting to try my hand at dissecting and repairing. if anyone has one that they are wanting to toss, I'd be happy to take it. I've been very interested in doing this and the local junk yards in my area doesn't have much at all for diesels.
 

dbrannon79

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@MrMarty51 message me! We can arrange shipping n all. Id like to setup a little project in the future trying to resurrect one and maybe remote mounting the transistors. Possibly finding some components that don’t need as much cooling to operate. A few years ago I replaced some mosfets in a power supply that were overkill for the application which worked perfectly and eliminated 80% of the heat it used to make. I know there’s other places that people have posted about trying to invent the perfect PMD but to me it’s a challenge and a hobby lol
 

jrsavoie

Recruit
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@MrMarty51 message me! We can arrange shipping n all. Id like to setup a little project in the future trying to resurrect one and maybe remote mounting the transistors. Possibly finding some components that don’t need as much cooling to operate. A few years ago I replaced some mosfets in a power supply that were overkill for the application which worked perfectly and eliminated 80% of the heat it used to make. I know there’s other places that people have posted about trying to invent the perfect PMD but to me it’s a challenge and a hobby lol
I've always said, since they are remote mounted, there is no reason to worry about size or bolt pattern. I never understood why somebody didn't come out with a bigger heavier duty unit.
 

dbrannon79

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I did finally find my old stanadyne oe PMD hidden under my back seat. It works but intermittently kills the engine. With a couple PMD’s to work with, I’ll try to source a large aluminum heat sink or plate and a spare long PMD cable to start with. Then start a thread with photos as I dissect them and research the components and their load capacity limits. We can all work together finding heavier duty parts

maybe others out there might have access to a schematic for the PMD itself!
 

Husker6.5

135' diagonal 16:9HD, 25KW sound!
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I used the aluminum heat sink, cut in half perpendicular to the cooling fins, from a fried 2HP 3Phase motor speed controller unit. A half is more than enough plate thickness, fin density and radiating surface area compared to the several styles of FSD coolers sold commercially by various vendors to handle the heat output of the two driver transistors of the PMD.

Sounds like you're trying to reinvent the wheel there, @dbrannon79 . Flight Services did pretty much what you propose to do with their upgraded PMD/FSD design (the licensed "new style" stepped unit they, Dorman and others also use and Stanadyne "borrowed" with a modified plug design) that basically used higher quality Mil-Spec driver components inside the circuitry that could literally take the heat and vibration of the stock PMD/FSD location. Remote located on a heat sink they are virtually indestructible.
 

dbrannon79

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I probably am reinventing the wheel. it's more of a hobby of mine loving to tinker around with failed electronics, especially when there is a known issue or failure rate. a hopeful goal would be finding components that virtually produce little to no heat and be able to mount in an enclosure inside the cab away from vibrations and the outdoor elements.
 

Husker6.5

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Heat will always be a factor when you are using power amplifying transistors - just look at the heatsinks and ducting fans inside any commercial PA audio amplifier like a Peavey, QSC or Crown for TO4 case transistors.

Now, the transistors in the PMD are indeed, 500 Watt transistors, in a push-pull arrangement. Now, that being said, despite comments on here elsewhere and in advertisements for certain PMD cooler vendors, they are not putting out 500 Watts of power/heat each! Not even close to it, by far! If they were, not only would they literally melt the circuit boards inside the PMD, they'd boil the diesel fuel inside the IP before it would make it through the pump. That's a 1,000 Watts total, the power of one of your burners on an electric stove!

They are switched on/off and are rated at 500W so that it is a clean power signal that does not clip. Look at the gauge of the wires in/out of the PMD plug. The continuous amperage draw and send from those two transistors couldn't be handled by those wires. The actual continual draw is about 30 Watts of the PMD, the total heat output of the two transistors is the same.

The two biggest problems with the OEM Stanadyne PMD are a result of GM's pencil pushers. Stanadyne designed their driver (the PMD) to be remotely mounted away from the IP and with a sink/radiator assembly (sound familiar?) The pencil pushers, accountants and engineers, the former balked at the additional costs associated with the parts required, the latter came up with the "solution" - over the protests of Stanadyne's engineers - of mounting the PMD to the side of the Stanadyne IP with the idea of satisfying the bean-counters by eliminating wiring and a heat sink while using the mass of the IP and the "cool" fuel flowing through it as a heat sink and dissipation method for the heat produced by the two power transistors. Only two problems with that. The IP is located in arguably one of the hottest locations in the engine compartment, in the valley with heat sources all around it (coolant crossover, intake manifold, heads) and then already poor airflow to cool it made even worse by that stupid plastic 6.5 Turbo engine cover.

Stanadyne's pencil pushers were also at work as far as the PMD was concerned, using standard tolerance components and only a basic design in the first series of "cigarette pack" black ones. Later versions of that one made by Stanadyne came out in the early 2000's added things like a limp mode that didn't shut the injection signal off completely and kill the engine when the PMD overheated, but that was mainly because GM/Stanadyne was tired of replacing IPs under warranty from DTCs for "failed" IPs when the PMD fried and vehicles were dying in to middle of nowhere or the middle of a traffic jam.

Late 2000's/early 2010's Flight Services, upon the expiration of Stanadyne's Patent, began addressing the problems of the OEM unit's failures, including its very high price. They did things like going to MilSpec circuitrt components that could handle higher temps and vibration, tighter tolerances and higher wattages on resistors and a thicker circuit board, all of which was plug and play compatible with the existing GM platform and mounting location. Around the same time Stanadyne came out with their "improved" PMD - the gray beast that uses a slight modification of the plug, necessitating either modifying the harness plug slightly or buying an adapter from - Stanadyne/GM.

The other benefit is that the Flight Services design is not only better than the OEM design, but cheaper in price than either of the Stanadyne designs, too. It wasn't very long after that that FS licensed the product and aftermarkets like Dorman was selling the FS unit under their label name.

Yeah, go ahead and tear one apart for curiosity's sake to see what makes one tick, but don't think you can build the better mousetrap and retire to Disneyworld for the rest of your life, that ain't gonna happen with this engine platform.
 
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