Engine/Transmission (1998.5 - 2002) Strange fuel pressure problem

[therobzilla]

This is on a friends truck. Installed an airtex pump with 3/8 line on the frame rail with a new VP44. This pumps pressure could be pulled down all the way to 2 or 3psi so a walbro pump was instaled with adjustable bypass regulator inline. Everything was great for a day or two and it held a steady 16psi. GREAT right? Within the next week it had slowly gone down to a steady 10psi. Reset the regulator and nothing happened. We thought the pump might be bad so we pinched off the return line and the fuse popped for the pump. Put a new one in it and it was at 45psi! The truck was immediately shut down and the regulator adjusted to 21psi. This could be pulled down to about 16psi WOT which was fine so we left it. In the next 3 days it had come down gradually to 8-10psi again! Now the FASS95 goes on. This should fix the problem, thats what everyone says. . It is run through the same draw staw5 [through the dealer installed "in-tank pump module"] with the same 3/8 lines all the way to the factory fuel filter can which is being utilized and has a clean new filter.



8 PSI!



Can somebody please help? Ive heard about a check valve that runs in line i n the VP44s return line. Could this be leaking down? Heres a link to the truck owners cumminsforum thread. Thanks guys!



HERE

 

[Joe Mc]

Checked out your buddy's post on CDF and replied



"it's possible that one of the hoses to, or from, your feed pump has failed internally and created a restriction/flap that is reducing the volume/pressure = making a check valve of sorts. I've had this happen on brake hoses, but it's a possibility that I haven't heard mentioned yet = worth checking out".



Since this is my first home (TDR) figured I'd place it here as well - you never know . . .

 

[DFerverda]

When you put on the fass did you eliminate the walbro pump?
Did you eliminate the bypass?


When i put in my raptor 100, i left the bypass for the walbro pump in place. After a few days i started having pressure all over the place, sometimes low then back up.
I took out the bypass (from the walbro) and removed the small screen at the inlet of the raptor,(i have a strainer before the pump anyway) and that cured my problem. The raptor did not play well with the bypass, it has it's own bypass built in, as i think the fass does.

Have you checked your fp gauge against a known good one.
Hope this helps.
Dirk

 

[therobzilla]

When you put on the fass did you eliminate the walbro pump?

Did you eliminate the bypass?





When i put in my raptor 100, i left the bypass for the walbro pump in place. After a few days i started having pressure all over the place, sometimes low then back up.

I took out the bypass (from the walbro) and removed the small screen at the inlet of the raptor,(i have a strainer before the pump anyway) and that cured my problem. The raptor did not play well with the bypass, it has it's own bypass built in, as i think the fass does.



Have you checked your fp gauge against a known good one.

Hope this helps.

Dirk

Yes, the walbro is gone as is the bypass for it. The gauge in the A pillar has been tested over and over against a known good pressure test gauge.

 

[DFerverda]

The valve for the return is on the vp44 beside the inlet. I have heard of a couple of them that caused trouble, but not many. Depending on where they bought the new vp, some supply a new valve some don't. They can be bought at the cummins shop.

What hose did you run from the draw straw out? Did you cut an angle on the bottom of the straw? How far did you gut the module in the tank?
I had a restriction in a piece of vulcan hose, the plastic liner was wadded up where i pushed in a fitting.
A way to test would be to unhook the line to the vp at the fass, install a T with a gauge and route the other end of the T back to the tank fill and put 12 v steady to the fass and let it circulate fuel and watch your gauge. You could crimp the hose to the tank Slightly to see what the gauge/fass does. That would eliminate a restriction in that section.
Dirk

Edit// I just caught the fact of the draw straw 5, so the straw would not need to be angle cut.