VP44 Overflow Valve

[glmoore001]

On top of my other mysteries, recently my Fass is acting up. Normally when I shut down the truck, the lift pressure gauge stays at 15 lbs even without the pump running. When the truck starts, the gauge would go to zero then immediately up to 15. The last couple of days, the pressure drops and takes about 30 seconds to get up to pressure again. After it gets there, it stays there and the pump acts normal.

The truck has no start issues.

What I have read points to the overflow valve on the VP44. I have found a diagnostic check procedure on how to check the overflow valve, but it involves checking at 10 psi air and 16 psi air and I have no regulator that will regulate that finely. Would a small leak also cause this problem? I am not getting any fuel smell.

 

[JR]

If your fuel pressure gauge is electric I would compare it with a manual test gauge first.

 

[GAmes]

Is it an Isspro EV2 gauge? Mine has always stayed at the pressure when I turned off the key, then dropped to zero and climbed to pressure when the engine is started.

 

[DavidC]

Is it an Isspro EV2 gauge? Mine has always stayed at the pressure when I turned off the key, then dropped to zero and climbed to pressure when the engine is started.

Yeah it is a stepper motor gauge. Takes a little getting use to.

 

[glmoore001]

Yes, but it is a new thing. I have had the truck for a year and a half, this is new behavior for the gauge.

 

[glmoore001]

It is an ISS Pro Gauge, new behavior for the gauge though.

 

[KATOOM]

DONT touch the overflow valve... Its nothing more than a checkball/spring inside a banjp fitting with a small bleed orifice, preset to obtain a set pressure parameter within the VP's first pressure chamber.
In the decades I've been part of these forums I dont think I've heard of anyone having to replace theirs.

The issue is either your fuel pressure gauge (which as pointed out, should be confirmed with a test gauge for accuracy), or its the FASS regulator. Since the fuel system is dynamic and doesnt hold pressure, I'm going to say its a faulty gauge or sensor.

 

[glmoore001]

Ok.. I will get a pressure gauge and do a manual check. Not something I was thinking of because the gauge has only been on there a year. Thanks to everyone for the advice... Gary

 

[JeepBuilder]

I just replaced a EV1 isspro gauge that was a little over a month old. The replacement fixed my lack of pressure and odd readings. I have faith in Isspro but as with anything, they can go bad. I almost went after the overflow valve too.
I hope your solution is as simple as mine was.