FASS fuel pressure issues!

Teelo

Teelo

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Jun 10, 2007
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143
My FASS was running really low fuel pressure... like I would turn the truck on and it would start at about 2psi and then slowly (and I mean slowly, like over 20 minutes) gradually build up to about 10psi or so. I replaced both the filters and I have the same issue! Filled both filters with fuel before I installed them so it shouldnt be air locked or anything like that. I can turn the truck on and loosen the bleed valve in the Water seperator filter and it will gradually establish a little pressure-I can hear and see it bleeding air out of it. When I loosen the front filter it overflows it like hell so its getting pressure to it, but the water seperator doesnt seem to be getting any pressure? Any help would be greatly appreciated! dont want the truck to shut off going down the road in gear :doh:
 
What gauge are you using? mechanical or electrical? Checking readings with a non-isolated mechanical gauge is always a good idea.

The W/S is on the suction side of the pump so it shouldn't be under pressure. Opening it while running would allow the pump to suck air in. I would bleed the system really well to eliminate the possibility of a vapor lock problem.

Is there a lot of flow to the IP?
 
I have a mechanical gauge. Tried bleeing it with the motor off and no change. Air comes OUT the bleed valve on the WS when the motor is on.
 
Could be an issue with your pick-up tube(drawstraw etc..)How much fuel is getting pushed back through the return line?Just a couple things to consider.
 
Do you have an isolator inline to the FP gauge?
Do you know what happened to cause this?


Out of curiosity I did a little test. With the pump running I loosened the WS- pressure drops instantly. Tighten the WS- and the pump won't prime and fails to build more than 2psi with very little return to the tank. So I took off the line to the IP, stuck the end in the filler neck and let the pump run for a few- the pump primed instantly and ran/flowed great with no restriction. Connected everything back up, bled the last bit and the pump pushes a steady 32psi again. Same thing happened when I loosened the drain w/ the pump running: first it sucked air in, the pump lost prime, then for me fuel gushed out, pump wouldn't prime with it tightened. Bled it again and its working fine.

Disconnect or at least loosen the line from the IP and let the FASS run for awhile. It should gush fuel out and prime itself. If it doesn't then work your way back down the system tell you find whats wrong. Pumping into or out of a fuel jug would isolate the pump.


Suction side air leaks are really hard to find because they are not visible. If you could pressurize the entire fuel system that would really be nice, but not everyone is able to do that. Make sure all suction side fittings are tight.

Let us know what you find with the return flow, and drawstraw
 
id def check your gauge. id check your fittings and run silicone spray in the line(yes silicone spray). i had the same prob and i thought it was my FASS. ended up being the gauge.
 
i think its the gauge... i can turn the truck on and with the gauge reading 0psi its all i can do to squeeze the fuel line going to the cp3 together. and i can feel fuel going through it too
 
Don't the later years like yours have the in tank pump? If so, I believe you need a draw straw. Just an idea.
 
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