Engine/Transmission (1998.5 - 2002) fuel pressures keep dropping, is it the FASS?

[Silver Bullet Ram]

I installed a FASS couple of weeks ago. First, It was at 16 psi. Then went to 15 psi, then to 14 psi, then to 13 psi and today I'm at 12 psi and its trying to move to 11 psi. WOT I can bring it down under 10psi. Any ideas? or do these pumps do this?



Gary

 

[eric01ctd]

Did you just get the pump or the whole setup? If you have an OEM fuel filter still, I would swap that out. I run the 95 GPH pump only and have a solid 20psi at idle and 15-16psi at WOT.

 

[Silver Bullet Ram]

I guess its the whole setup, it came with a water seperator, fuel filter, brackets, fuel line.

 

[Eric Lee]

I have had my FASS for a couple years now - plumbed in to the input of the stock fuel filter can. My pressure gauge is tapped at the bottom of the stock can to read the pressure after everything but the last fuel line -which has large hole banjos. I ran without the stock filter in it for awhile and for some reason I put a new filter in it the last time I changed the FASS filters. I thought if 2 filters were good 3 would be better. I have been noticing a slight fluctuation of pressure 12-14 psi that use to be a stable 13. 5. I think I'll take out the stock filter from the can and see if it returns to the original pressures.



- Eric

 

[Silver Bullet Ram]

I don't have the filter in my canister, however I am running into the canister.

 

[Eric Lee]

I don't think filter in or out is the culprit. If the filters are fresh and there isn't any obstruction - if there is really a problem and it's not a trait of the system - my guess is that somewhere we're sucking air.



I started researching reasons for erratic pressure (ended up being the gauge) with the FASS. I was told by more than one source it might be the fuel pick up tube in the tank. Fatigue cracks develop I guess and pressure might fluctuate with fuel level.



I actually bought everything to make the pick up tube modification before finding it was the gauge. Basically a bulkhead fitting, a piece of hardpipe and some hose. It's a pain in the *** mod - but as old as our trucks are getting I think it's possible the pickup tube could have fatigue cracks and sucking air. I didn't want to believe it then - I don't want to believe it this time either - in fact I'll look at everything else before I monkey with the assembly in the tank.





- Eric

 

[PBliss]

I had a similar problem with my walbro, at idle 18-20 and at wot as low as 3. After lots of frustration adding filters, adjusting the regulator etc. it turned out that the fuel tank had black sludge in it that plugged up the pick up tube and screen around the pick up. Since it has been cleaned pressure stays 15-16 WOT.

 

[rkressg]

I had a symptom similar to that a few years ago. It turned out that I was sucking parts of a destroyed fuel float into the fuel pickup assembly in the tank.

You can try the 5 gal bucket test just to ensure that the pump is working properly.

Also, if you have the Fass with the filters, I would remove the fuel canister completely and just run the fuel lines directly to the VP44.
-Rich

 

[GCULP]

check your guage, simple things first. I have had the nylon hose fittings from the isolator to the guage loosen up or loose their seal and bleed off pressure. also just check the pressure using a mechanical guage at the VP44.

 

[LowFly]

Sounds like you got a classic isolator bleed-off issue. You got one? If you do, did you rebleed the diesel side after you installed the FASS? BUT, we see most issues on the gauge side with the coolant. If you have one, i would start here.

 

[Silver Bullet Ram]

I have a Westach with the electric sending unit

 

[Silver Bullet Ram]

Here is another strange thing, I stop or turn and the fuel pressure goes up a little bit.



Gary

 

[LowFly]

Here is another strange thing, I stop or turn and the fuel pressure goes up a little bit.



Gary

HUM... that is weird... . BUT being electric... i would double check with a diesel fed mechanical gauge in there to make 100% sure its reading correctly... ...



Its werid that a FASS would show this issue... . BUT normal pressure is about 13-14 PSI if its a 150/95 or 150/150.

 

[jhoughton]

Try disconnecting the fuel hose into the pump then take about 20 psi and blow back into the tank. This will clear the screen temporarily. This will tell you if you are picking up trash at the pickup tube. I did this on mine more than once trying to find my pressure problem. Mine was at the isolator for my pressure gauge. But yours could be in the tank. Also as stated above check pressure with a mechanical gauge. That will rule out your sender. Good luck with this. My FASS is great never below 14 psi and quiet to me.



Jim

 

[Silver Bullet Ram]

HUM... that is weird... . BUT being electric... i would double check with a diesel fed mechanical gauge in there to make 100% sure its reading correctly... ...



Its werid that a FASS would show this issue... . BUT normal pressure is about 13-14 PSI if its a 150/95 or 150/150.

I checked it with a mechanical, same psi so the electric is working.

 

[Silver Bullet Ram]

Try disconnecting the fuel hose into the pump then take about 20 psi and blow back into the tank. This will clear the screen temporarily. This will tell you if you are picking up trash at the pickup tube. I did this on mine more than once trying to find my pressure problem. Mine was at the isolator for my pressure gauge. But yours could be in the tank. Also as stated above check pressure with a mechanical gauge. That will rule out your sender. Good luck with this. My FASS is great never below 14 psi and quiet to me.



Jim

I'm beginning to wonder that too. Before the fass, I she up and quit at a 1/8 tank.

 

[Eric Lee]

I haven't monkeyed with the isolator since I put the mechanical in - 1 or 2 years ago. I hate to say it but don't think I ever bled it. I guess it's easy enough to do, just recharge the antifreeze and crack the fitting? Same with the diesel side?



- I'll check that first and then back flush air into pickup tube. I use the same busy fuel station most of the time and go through it pretty quick. Never any bio-diesel. I don't think that's my problem but the checky check is easy enough. I also have fluctuation tied to trucks attitude.



I'm suprized nobody else has seconded the crack in stand pipe theory. That seemed to be a popular cure idea not so long back - even Piers' guys suggested it.



- Eric

 

[Silver Bullet Ram]

What is a stand pipe? Is that the suction tube?

 

[Eric Lee]

I'm probably using the wrong term - 'pick up tube' is most commonly used. The tube that is inside the 'fuel tank module' that the pump uses to pull the fuel off the bottom of the tank.



- Eric

 

[GCULP]

yup, pick up tube or draw straw. as for the mechanical guage, did you test it while driving to recreate the same symptoms or just at an idle. reading through the other symptoms it's beginning to sound like a pick up issue, or the connection at the top of the take where the supply and return lines connect.