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post #2 of (permalink) Old 06-09-2010, 10:44 PM Thread Starter
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I initially thought the cavity under the computer/heat sink held the supply and return ports. Only the fuel inlet is connected to the cavity. The fuel enters this cavity makes direct contact with the computer heat sink and is forced thru the orifice ( http://www.turbodieselregister.com/u...&albumid=17275 ) to the vane pump and to....take a look at the diagram. ( http://forum.mopar1973man.com/showth...sure-suggested...
) BlueChip has said that the majority of failed VP44s is due to failed computers (at least with the later versions). The computers fail because they get too hot and/or because of heat cycling, in particular the lead-free solder connections are weakened by this. Chip noticed (I don’t know how) that the temperature gets the hottest right after shutdown….makes sense, because no more fuel is flowing thru the pump for cooling….when the IP is not turning no fuel will pass thru it. Chip is currently working on two things to remedy this; one modification will allow fuel to flow thru the pump (just the heat sink cavity) even when the IP is not turning, the other will allow the lift pump (LP) to continue pumping (and circulate fuel thru the cavity) after the engine is shutdown until the pump is “cool enough”.

Chip has tested different solutions to this problem in the past. He’s spent over $10k trying to move the computer, but electrical interference put that solution to rest. He machined and bolted another heatsink to the top of the computer, actually I think he machined a whole new cover with integral heat sink….said the temps underhood are too high to do any good. I''m not clear on how or where he measures pump temps to test his solutions.

I asked Chip if the current solutions he’s working on include adding another outlet port to the cavity, but he stopped me there with proprietary. I believe that is a good solution, especially if you can add the port to the opposite side of the cavity….if it is feasible given the layout of the IP. I’m thinking you would attach a regulator on this added outlet port and maintain the cavity to say 17psi and use a higher flowing LP. I have an AirDog LP/filter assembly, I believe rated at 95 gph with big feed line, stock return line, not sure if I got a different pick-up. As it runs now, most of the LP flow is returned to the tank right from the pump exit, the fuel returned from the IP and injectors shouldn’t have change much, if at all, with the addition of the AirDog. Adding an outlet port with regulator to the cavity would allow much more of the LP flow to actually go to and cool the IP computer.

I've got great pics, diagrams, and cut aways of the VP44, but I have them all in a word file that is too large to upload, and I can't get the pics out of the word doc!
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