Archived Replaced fuel filters and now pressure problem

[Turboman]

I have a FASS 150 pushing through the factory fuel filter. I changed the FASS filters and the factory filter and now my fuel pressure fluctuates at idle and drops to zero when you rev it up. I tried different filters, checked everything, even installed a rebuilt FASS system, same thing. With the engine off and pump running pressure stays constant at 18-20, with engine running it jumps all over and drops like a rock when you floor it. I even changed the fuel return check valve on the VP44 next to the fuel inlet. Same results. Any help would be great appreciated, I have sold this truck and need to deliver it wed or thurs.

 

[BIGNASTY]

I have a cp3 pump so I dont know if it would be the same as your VP44 but do you fill your filters with fuel before you put them on. It mite be air trapped until it gets it out of its system. My son has the sister to my truck and he didnt pre fill filters and he said it ran funny for a while. He has no gauges so he could tell the pressures just a thought

 

[Turboman]

I might add I changed filters the same way I always have and never had this problem, it usually smooths out after a few minutes. And when I open the water drain on the engine mounted filter with the FASS running it pumps fuel out like crazy. I'm going to check pressure with a mech guage tomorrow and check the sender connections.

 

[JLandry]

Turboman,

I've experienced this same thing and I suspect it is caused by trapped air pockets in the fuel system. A few suggestions that have worked for me...

1. First, get a second opinion on the fuel pressure by using a test gauge connected to the fuel inlet of the VP44. I can't tell ou how many times the fuel pressure gauge in my truck has given me inaccurate readings for one reason or another. You'd sure hate to find out the fuel pressure is fine while you've been wasting time and money chasing down a nonexistent problem. You can buy an inexpensive fuel pressure test set at any auto parts store.

2. Remove the fuel line from the inlet of the VP44 completely and stick it in a coffee can (or other suitable container) and then bump the starter to activate the lift pump. This will help aggressively purge air out of the fuel system if there is any. You may want to do this several times just to be extra sure you get all the air out.

3. If you're using an isolator with your fuel pressure gauge, you may need to bleed the air out from between the pressure source and the isolator.

4. Are you sure there's an adequate fuel level in the tank? Try adding 5 or more gallons of fuel and see if that changes the pressure behavior.

Please keep us posted on how things turn out.

John L.

 

[Turboman]

fixed it, bad connection at pressure sender, Thanks for your input

 

[JLandry]

Good to hear!