Fass HD Runs but low pressure

stibuilder

New member
Oct 17, 2016
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Snoqualmie, WA
About 3 months ago the my fuel pressure gauge that usually reads 10/9 psi jumped up to 21 and then started doing weird stuff bouncing all over the place. I chocked it up as a bad sending unit (Autometer) the other day I changed both the filter and water separator, along with the sending unit and no change. Gauge reads max 6psi and then after driving it goes to 0 if I get on the throttle.
I added a mechanical gauge today and when my digital reads 6 they both read 6 but when the digital reads 0 the mechanical reads 2/3 roughly. Both are in the FASS filter replacement bowl.

Its a pretty old unit SN 27305, should I buy a new pump or just a motor or a whole new unit?
 

snowman22

Member
Jan 30, 2018
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SoCal
Sounds like a good time as any to see how FASS stands behind their product. I know they have a warranty card that says it must be turned in for warranty in the future, but you never know until you try.
 

stibuilder

New member
Oct 17, 2016
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Snoqualmie, WA
Talked to tech support they think its the return spring, advised I pull the fitting and stretch the spring out 1/4" and see If that helps any.
 

stibuilder

New member
Oct 17, 2016
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Snoqualmie, WA
Got a new spring and ball from FASS, and the new spring is 1/4" shorter than the spring I stretched, and it made the fuel pressure worse. Now it never shows positive pressure, on the stretched spring it showed 5-7 at times and then would go to 0. Should I try and rebuild the pump or just buy a new setup?
 

stibuilder

New member
Oct 17, 2016
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Snoqualmie, WA
Well its not the Pump, we replaced the pump motor today and same thing no pressure :(
We went on to build a new feel line to make sure the old line wasnt sucking air. Still no pressure. Wondering if there is some issue in the oem filter housing? My hunch now after we took one of the return springs in the FASS system and i stretched it out pretty far and it made 5psi for a bit then went to 0. Truck wont make any fuel pressure with just the pump running an the engine off. To make sure we put a physical gauge on and the same results.

Is it possible the factory filter head is just returning the fuel? Pressure is being measured from the FASS filter delete bowl things.
 

nmband13

Member
Jan 17, 2011
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Sioux Falls SD
I recently worked on a customers truck which had a poor GROUND for the pump. Power was good but the ground was bad and was causing issues.
 

2004LB7

Well-known member
Dec 15, 2010
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Is that to the pump? Because I think the posts are referring to the "from the pump" wiring. If you have voltage om the negative wire then you have a bad ground connection
 

stibuilder

New member
Oct 17, 2016
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Snoqualmie, WA
Pump is running great, after replacing the filter head with a new one and running pressure sensor off the bleed screw we got the same thing no pressure unless I pumped the priming plunger. Now today we just so happened to crack the fuel tank fill cap and noticed a seriously high amount of fuel being returned to the tank. Is there something we are missing?
 

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
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At Da Beach
They have 2 piece soft lines so the inner line can collapse and it look visually fine. The lines on my LMM did this, I ran all new fuel lines and truck was much happier...
 

JoshH

Daggum farm truck
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Feb 14, 2007
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When you installed the FASS filter delete bowl, did you remove the check ball?
 

stibuilder

New member
Oct 17, 2016
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Snoqualmie, WA
When you installed the FASS filter delete bowl, did you remove the check ball?

Yes, and when i put the new filter head in with the oem filter I didn't change anything. I installed it as is, and just put in an adapter at the air bleed screw to go to the sending unit.