How about running the lift pump post shut down to cool PMD?

[914turboford]

I have been reading quite a few threads about preventing PMD failure. It seems that some think the cooling effect of the fuel for a stock mounting is adequate but that post shut down heat soaking is the main culprit in PMD destruction. I am wondering if anyone has tried running the lift pump after the engine is shut down. This would keep fuel circulating through the IP, thus cooling the PMD. This could be controlled with a simple temperature switch like those used to cycle an electric cooling fan. The switch could be mounted near the IP or wherever. You can buy adjustable fan switches for $40 or so. This would result in excess wear on the lift pump, of course. However, unless you do a lot of short trips it would be a fairly small increase in run time as a percentage of total time. And lift pumps are cheaper and easier to replace than PMD's. Any thoughts?
Brian

[Jim Faire]

... doesn't like that idea.

Not because it won't work; in fact, it's not a bad thought at all for preventing damaging 'heat soak' of the PMD. Wish I would have thought of it.

However, since I didn't, I can join in by shooting it down.

The Lift pump is controlled by the PCM and OPS, and the whole circuit is set up to shut it down in the event of engine stoppage.

Which could be caused by an acci-crash. The purpose of this little modification is to keep from having an overly-conscientious lift pump continue to pump diesel onto a fire for extended periods of time after some schmuck T-bones you and you're too busy being out cold to shut the truck off.

Good thought, though...

[DA BIG ONE]

Look into mounting the FSD in the air flow to radiator because of the cfm flow it will cool quickly w/short switched hi-idle (1,000+ rpms)time before shutdown, I use pyro meter (EGT pre-turbo) gauge for shut down @ around 275 deg (f). I have the cooling fins facing forward and above bumper line on one of my main FSD cooler w/other FSD's as spares.

[914turboford]

it's not a bad thought at all for preventing damaging 'heat soak' of the PMD. Wish I would have thought of it.

However, since I didn't, I can join in by shooting it down.

The Lift pump is controlled by the PCM and OPS, and the whole circuit is set up to shut it down in the event of engine stoppage.

Which could be caused by an acci-crash. The purpose of this little modification is to keep from having an overly-conscientious lift pump continue to pump diesel onto a fire for extended periods of time after some schmuck T-bones you and you're too busy being out cold to shut the truck off.

Good thought, though... Now that was funny. What if I add a little safety wrinkle to the idea? Put an impact triggered switch like those found in 80's/90's Fords (not sure you can use that word on this forum, moderators feel free to remove it) in the circuit.

If this idea is worth further consideration, I wonder how long the pump would have to run to prevent heat soak. One hour or more? I think the batteries could run it for quite some time but if it took too long (hours) it might be impractical.

[DennisG01]

After market keyless entry/starters will alot of the time have a "cool down" feature for turbos. It enables you pull your keys out, lock the truck and walk away. The engine will keep running for a pre-determined amount of time and then shut-off.

[Warren96]

This deserves some consideration. To expand on that idea, How about opening the bypass return line at shutoff,with the pump running, with an adjustable time delay relay to turn it off. Barnet has them for less than $10. I wish I had thought of this!

[914turboford]

This deserves some consideration. To expand on that idea, How about opening the bypass return line at shutoff,with the pump running, with an adjustable time delay relay to turn it off. Barnet has them for less than $10. I wish I had thought of this!
How does the bypass return line open? Is there a valve for it on the IP? The Barnet timer you mention, would you have to manually set it? If you use a thermal switch you wouldn't have to set it when you shut down, it would be automatic.

[AndyL]

The DS4 "return" is a positive type pump, no fluid will run though without it in rotating operation.

[DickWells]

A couple of thoughts come to mind::)
*Shouldn't you already have a relay hooked up to the lift pump to take the electrical load off the OPS?
*Though the post shut-down pump is a good idea in a sense, why would you not just remote mount the PMD/FSD that you'll be buying sooner or later, anyway? No need to remove the old one from the pump.

DW

[914turboford]

I'm thinking that the designed in liquid (fuel) cooling might be superior to air cooling anywhere on the truck, except for right by an AC vent in the summer time. I think the problem with these things is post shut down heat soak, which my idea addresses. But I could be wrong. Wouldn't be the first time.

[Jim Faire]

I'm thinking that the designed in liquid (fuel) cooling might be superior to air cooling anywhere on the truck, except for right by an AC vent in the summer time. I think the problem with these things is post shut down heat soak, which my idea addresses. But I could be wrong. Wouldn't be the first time.

"... be superior to anwhere IN the truck..."

Put the darn thing outside the engine compartment, being very careful and picky about how it's heat-sink'd and weathersealed, like Bill Heath did, and forget about it.

Or try new and funky things to try and make the engine compartment survivable. It's an interesting exercise. Pointless, but interesting.

[914turboford]

Or try new and funky things to try and make the engine compartment survivable. It's an interesting exercise. Pointless, but interesting.
Isn't part of the point of this forum to discuss inovation? Why not discuss the idea on it's merits or lack thereof?

Unfortunately the idea seems to be dead if the fuel will not cycle past the IP without the engine running.

[Robyn]

Just to reinforce what has already been said.
The Lift pump MUST be off when the key is off. The issue of a continued supply of fuel in the case of an accidient must be addressed.

Also as has been mentioned, there will be no fuel running through the IP once the engine is shut off.

Move the PMD out front into the clear air behind the grill on a heat sink with fins. This is simple, it works and its cheap and it does not compromise the rigs safety.

The cooling effect of the IP and the "COOL" fuel is pretty lame considering the fact that the temp down in the hole is high anyway.
Trot out sometime after a good long run on a hot day and while the engine is still running and before the heat soak takes effect and touch the IP.

You wont hang on long I gaurantee it.

The PMD issue has been thrashed out so many times that its pretty much a science now.

Move it to a cool spot with lots of air flowing and get on with life.
New ideas are great but I cant really see compromising the fuel shutoff safety especially when no fuel will circulate anyway.

Not to toss cold water on the campfire but sometimes things just wont work.

best

Robyn

[Robyn]

Just to add some interesting items.

Back in the day when the DS4 was hatched the IP and its components were and are a property of Stanadyne as is all the engineering.

There was I am told a pissing match between GM and Stanadyne on how some of the controls were to be done and the interface you see is how they did it.
IIRC GM wanted the driver in the ecm or at least some other place.
Stanadyne did not want GM having access to their engineering so they ended up with the PMD on the pump so that is kept the IP and its tech seperate from GM except for the little plugin to hook it up

Had GM prevailed then the issues we see may never have happened.

The idea of having transistors mounted in such a hot environment is obsurd anyway.

Just turn off the CPU fan in your Puter and see how long until it takes a poop. "NOT LONG"

This is just one of those things that really gripes me. The DS4 should never have been released untill all the bugs were out and the pissing matches had been resolved.

Many of the issues with the IP itself were fixed over the course of the first couple years of production. The PMD did see some updates but the basic design remained until the end and we the end users are now left to struggle on with a POS that will never be fully reliable.

Granted many of these little boxs operate for years and thousands of miles without so much as a whimper. MOST DONT though and they never fail at an oportune time.

The relationship between GM and Stanadyne I am told was strained to say the least.

This sort of operating condition is not a good thing when you are trying to build a quality product.

This has proven out in the end result.

I doubt that the new stuff being produced for the military will use this system as it is not a setup that can safely go into harms way.

I dont know for sure but will assume that AMG is still using the DB2 or something very similar for the HMMWV

Just a little tid bit

Robyn

[Warren96]

UH oh, Robin just threw water on our campfire. The timer I spoke of is adjusable, but how could you get the fuel back to the tank?

[JohnC]

Many have said
Also as has been mentioned, there will be no fuel running through the IP once the engine is shut off.

The issues surrounding having the pump running with the engine off not withstanding, I don't believe this is true. I base my statement on 2 things. First, I have an old article on the DS4 pump that seems to show a path for the fuel around the transfer pump, through the housing and out through the pressure regulator, then back to the tank. Secondly, if there was nowhere for the fuel to go, the lift pump would not run on after the key is off, at all. If you don't believe that, dead head the pump and see what happens.

Easy enough to test. Pull the return line off and run the pump. If fuel comes out, 'nuf said!

All that said, we ran a survey here a few years back on FSD longevity, and the only report of life after 200K was for a driver mounted in the stock position.

[AndyL]

I have a pressure gauge post lift pump, it holds pressure for several minutes after I shut it down.

[JohnC]

Yes, there is a housing pressure relief valve. Any time the lift pump pressure exceeds the relief valve setting, fuel will flow and the pump will keep pumping. When the pump stops the pressure drops to the valve setting, the valve closes, and the fuel stops flowing. If the pump is powered and the pressure downstream of the pump exceeds the pump's minimum setting, due to a restriction or the like, the pump wil not "click" until the pressure bleeds down to the pump setting. This is why the pump rattles rapid fire when filling a new filter but assumes a slower more regular cadence once the air is forced out.

[TurboDiverArt]

I have been reading quite a few threads about preventing PMD failure. It seems that some think the cooling effect of the fuel for a stock mounting is adequate but that post shut down heat soaking is the main culprit in PMD destruction. I am wondering if anyone has tried running the lift pump after the engine is shut down. This would keep fuel circulating through the IP, thus cooling the PMD. This could be controlled with a simple temperature switch like those used to cycle an electric cooling fan. The switch could be mounted near the IP or wherever. You can buy adjustable fan switches for $40 or so. This would result in excess wear on the lift pump, of course. However, unless you do a lot of short trips it would be a fairly small increase in run time as a percentage of total time. And lift pumps are cheaper and easier to replace than PMD's. Any thoughts?
Brian

Just mount the PMD and heat sync outside of the engine compartment and it'll cool down much faster than the already heated fuel ever could. I have mine mounted behind my bumper on the driver side. I can drive it for an hour and when I pull in and turn the truck off both the heat sync and the backside of the PMD are ambient temperature.

Art.