Fuel Return / Lift Pump

[CareyWeber]

Morepower / Kennedy / John C / GMCTD / Others,

Issue heat soak of FSD/PMD.

Would there be away to cause the lift pump to pump fuel to the DS-4 and cause it to bypass and return the fuel to the tank while the truck is not running which would allow the pump mounted FSD/PMD to be cooled. If the lift pump was powered via a timer at engine shutdown how long would it need to run to cool the FSD/PMD.

On a side note is there away to increase the rate of the fuel to the DS-4 so that more is bypassed back to the tank to keep the DS-4 cool?

Carey

[tom.mcinerney]

Carey--

Ucal Davis posted a while back that there was a restriction pumping thru FIP when stopped. It might be worth doing a test {LP (on/hotwired) Ig (off) Fuel Shuttoff Solenoid (on)} to ascertain if this holds when FShuttoffSolenoid energized.

GMCTD has posted that a downside of using an over spec'd (press or vol) LP is that excess fuel returning to tank will FOAM.
***
Sorry to request a test....if it pumped freely, your idea would negate FSD effects of heatsoak, though might want heat Xchanger in return line.
Another possibility wpuld be to pump ambient air thru In Man to Ex , would cool engine quicker--or an electric rad fan cycle....

[gmctd]

DS-4 transfer pump pressure is regulated from ~20psi at idle to ~125psi at full power.
Lift pump supply at 4-7psi would not overcome housing pressure requirements for bypassing to return line.

Lift pressure is low to prevent pressure variations from altering timing and injection events.
DS4 advance piston is actuated by housing pressure, same as DS2 pump.

Good thinking - would have been useful, but all indications say no.....

No way to increase lp pressure, but installing a second in series would pump from pressure base out of first - 7psi out of #1 gives 14psi out of #2.

One-way valves in #2, when off, would not block base pressure out of #1.