Bob20

The fuel return line which returns the excess fuel which is used to cool the VP44 to the fuel tank is connected to the VP44 by a check valve. The check valve opens at 14-16 psi. Consequently, I do not see how an intank fuel pump that has as output of 6-8 psi can supply any cooling to the VP44.

Any comments?

Bart Timothy

Something to think about. Do you think the VP44 is cooler while the engine is running with 6-8 pis fuel pressure, or after the engine is shut down and heat soak gets to it?

Bob20

Bart, anyone with an infrared thermometer and a second generation truck that has been converted to the replacement intank fuel pump can quickly and accurately answer your question.

I can only speculate based on my experience with hydraulic pumps. I believe the operation temperature would be higher than the heat soak temperature. Rarely can equipment be seccessfully operated in a manner more severe than it was designed for. Unless the check valve in the VP44 is replaced with one that will operate in the 4-6 psi range, the pump will not have the cooling fuel flow it was designed to have.

I believe the trucks with the intank pumps will have frequent electronics and mechanical failure of the VP44 due to the excessive temperature it will operate at.

ramtd02

The PRV on the VP44 relieves pressures above 8 psi. This is the info i received from Bosch anyways. And to chime in about operating temps. With my infra red, the VP44 gains 4.7*C after shutdown.

Bob20

Ramtd02, your information that the check valve opens at 8 psi sounds logical based on the threads I have read about the indicated output pressure of the intank pump.

However, I checked my neighbor's official Daimler Chrysler Corporation Service Manual for his 2001 truck.

It indicates that the check valve opens at approximately 14 psi and contains a detailed step by step procedure for checking it. The instructions indicate that if the valve does not open between 14 and 16 psi it should be replaced since it is not adjustable.

I will see if my neighbor is willing to remove the check valve from the VP44 on his truck so we can determine if it opens at 8 or 14 psi.

nitrousn

Most lift pumps dont reach 14. This vp fuel cooling is not the issue. I think its more ambient and soak heat that hurts the vp electronics than lack of pressure. I will agree on failed lift pumps causing injection pump failure, but thats due to little or no fuel supply causing failures.

slim51015

The VP has a vane pump that feeds the main pump. I believe the excess fuel this pump makes opens the overflow valve and returns the fuel to the tank. The 01 manual says about 70% of the fuel is returned to the tank.

nitrousn

That makes more sense. The VP creates the pop off pressure and not the lift pump. Good info.

jaxworks

I have a bud that works for the Dodge dealer here and he says the part about 70% return is right and on a hot day with hot asphalt road conditions and not much fuel in the tank that the fuel can get pretty darn warm...

high country

I can't imagine all that vibration is any good for sensitive electronics, heat is bad, haet and vibration, really bad, heating-cooling-heating-cooling mixed with vibration, really really really bad.

J BODY

I replaced about eight VP's (including mine) last summer in a two week period when we got our first "heat wave". It was 128 ambient. With my Raytec gun the off the road temp was around 164 degrees. Throw in underhood heat and you can see where this is going.....

RowJ

I don't see where you are going...or what your saying. "Off road Temp" ?? What measured 164*...?
Sorry, just want to be clear what your saying.

RJ

BigBlue

The temp coming off the road's surface was 164*. Add that in with the 128* ambient air and the underhood heat and you can imagine how hot everything is getting.

cditrani

Even with a dead lift pump the VP will pump fuel out of it's bypass. As someone mentioned, the internal low pressure vane pump is there to ensure enough internal fuel pressure on the low pressure side for the various hydraulically assisted mechanisms (like the timing mechanism) and to ensure cooling fuel flow.

My personal opinion is that all the VP really wants out of a lift pump is enough pressure on the VP intake to ensure there's never a vacuum condition caused by the internal vane pump (and therefore never any cavitation). Unless you have a huge HP truck and run it up past the redline all the time, I think a few positive PSI would do it.

I think it's very smart to keep your tank topped off when the temp is nearing 3 digits F.

RowJ

Thanks Blue! Just kept putting the comma in the wrong place (in my mind).

For those concerned... it's worth being aware of the serious tests done on temp of fuel being returned to the tank by the injector pump.
Several studies have shown that the temp of the fuel in the tank runs 15* above outside air temp... under most driving conditions and under all loads (incl. towing), with a tank level above 1/4 full.
I myself did a test for another web site.... 6,000', gross wt, full tank with outside air at 85*. I ran 400 miles, non-stop, Interstate at 75 mph ..... pulled over and immediately used heat gun on the fuel tank. It read 99*, 100* & 101* in three different places.

The heat soak, after shutting down, has been found to raise fuel temps 50* (heat gun on VP-44 casing with hood left opened) which may be the cause of electronic failures in VP-44's. But while running down the road... fuel temps passing through the VP-44 don't appear to be a serious problem.

RJ