starting about 2 weeks ago my 5.9 cummins seems to lose prime everytime i go to start the truck, i have a fuel pressure gauge and it reads 0 when i put the key in accessory mode, while the fass 165 is running i go and crack the filter open till it bleeds out fuel then i have the 17 pounds of pressure and it doesnt dip at all, but when its primed it sounds like its sucking air, im assuming its a return line somewhere but not too sure, truck runs and drives without skipping a beat when it has all the pressure it needs, but its literally every time i turn it off i have to re-prime the system, was looking for leaks and cant seem to find any at all, could it be a bad lift pump? fuel filters? ive read it can be the o-rings for the cross over tubes so im gonna start with changing those but no leaks anywhere is really confusing me, any help is appreciated.

 

Where is the check valve to hold pressure on the system when the pump isn't running?

 

i have no idea

 

Neither do I.

 

i imagine its on the fass ill look into it this weekend

 

If the fass is drawing air, you have an issue with a filter seal ring, or water drain, possibly a suction hose.

How is the FASS drawing fuel, sump, draw straw, factory module connection? Does it act worse on an empty tank vs full tank?

 

does not matter how full tank is, the old owner hooked it up to the factory module, at least i beleive so, i ordered a sump because i have the 1/4 tank issue aswell, but i have noticed it doesnt lose prime when the face of the truck is facing up hill, mainly because the only place i park uphill is my driveway and its always primed when i go to start it