Lift pump Mystery - Competition Diesel.Com

anwkid · 06-27-2019, 05:15 PM

Ive got a 97 12v that Ive extended the frame on to fit a 12' Douglas service body. Everything from behind the cab is new including the axle and frame. I ended up using a fuel tank out of a 2010 Ford that is mounted just behind the axle. Ive redone the entire low pressure fuel system and return with ptfe AN hoses and steel hard lines. I have a 50micron water separator and a 2 micron baldwin filter in the pressure side before the p pump. The air dog Raptor 150 is mounted at the tank and has a 1/2" feed into a draw straw into the tank. its about 3' of suction hose from the end of the draw straw to the Raptor. I used the original ford tank return line.

The truck makes 30psi when i click on the pump and humms away quietly like it should, but when i start the truck the pressure drops to 15-20 psi and the Raptor gets really loud like its cavitating. The pressure steadily drops throughout the day for a couple hours untill there is no pressure.

This is the third pump that ive tried (pretty sure its not the problem) and its been similar with all of them. Ive tried opening the tank fill cap to see if its vapor loc but no change. Any ideas??

jasonc · 06-27-2019, 07:14 PM

Has to be a restriction in the inlet. I'd pull the tank and the sending unit and look at the pickup tube good.

anwkid · 07-01-2019, 11:50 AM

I was using the ford pickup assembly which is 3/8”, and I thought the same as you, so I just put in a 1/2 draw straw and 1/2” hose to the pump inlet, it’s cut at an angle on the bottom so it can’t suck to the bottom of the tank, and same thing???

BigPapa · 07-01-2019, 12:02 PM

What about your return line?

06-27-2019, 05:15 PM	#1
anwkid Name: anwkid Title: Diesel Enthusiast Status: Not Here Join Date: Dec 2010 Location: Visalia, Ca Member`s Gallery Posts: 122	Lift pump Mystery Ive got a 97 12v that Ive extended the frame on to fit a 12' Douglas service body. Everything from behind the cab is new including the axle and frame. I ended up using a fuel tank out of a 2010 Ford that is mounted just behind the axle. Ive redone the entire low pressure fuel system and return with ptfe AN hoses and steel hard lines. I have a 50micron water separator and a 2 micron baldwin filter in the pressure side before the p pump. The air dog Raptor 150 is mounted at the tank and has a 1/2" feed into a draw straw into the tank. its about 3' of suction hose from the end of the draw straw to the Raptor. I used the original ford tank return line. The truck makes 30psi when i click on the pump and humms away quietly like it should, but when i start the truck the pressure drops to 15-20 psi and the Raptor gets really loud like its cavitating. The pressure steadily drops throughout the day for a couple hours untill there is no pressure. This is the third pump that ive tried (pretty sure its not the problem) and its been similar with all of them. Ive tried opening the tank fill cap to see if its vapor loc but no change. Any ideas?? __________________ 2003 QCSB 2wd, lowered, super special 64, arson III, II 100 horse injectors, Smarty SSR, TnT PowerMax, light port work, somewhat built tranny. Best of 12.71 @111.92 on street tires

07-01-2019, 11:50 AM	#3
anwkid Name: anwkid Title: Diesel Enthusiast Status: Not Here Join Date: Dec 2010 Location: Visalia, Ca Member`s Gallery Posts: 122	I was using the ford pickup assembly which is 3/8”, and I thought the same as you, so I just put in a 1/2 draw straw and 1/2” hose to the pump inlet, it’s cut at an angle on the bottom so it can’t suck to the bottom of the tank, and same thing??? __________________ 2003 QCSB 2wd, lowered, super special 64, arson III, II 100 horse injectors, Smarty SSR, TnT PowerMax, light port work, somewhat built tranny. Best of 12.71 @111.92 on street tires

07-01-2019, 12:02 PM	#4
BigPapa Name: BigPapa Title: Truckless Status: Not Here Join Date: Jan 2008 Location: Springfield, TN Member`s Gallery Posts: 5,034	What about your return line? __________________ Scott 2003 Avalanche Z71 Common sense is like deodorant. The people that need it most never use it.

06-27-2019, 07:14 PM	#2
jasonc Name: jasonc Title: Too Much Time Status: Not Here Join Date: Nov 2009 Member`s Gallery Posts: 4,412	Has to be a restriction in the inlet. I'd pull the tank and the sending unit and look at the pickup tube good.