Fuel pump

Reply Subscribe

Thread Tools

Search this Thread

Feb 7, 2021 | 11:23 AM

#16

FuzzFace2

FTE Legend

Joined: Nov 2015

Posts: 30,917

Likes: 4,123

From: Angier, NC

I do like what Digger is saying of the loops in the system as it does kind of make since.
As to why the other truck runs the way it does might just be pure luck or a HP pump in tank feeding a HP pump on the frame rail?
What would happen if you were to pinch off the return line with the tank pump supplying the HP pump would it stay running?
I would think if the tank pump could not supply the fuel to the HP pump closing off the retune it would / should stay running till it maybe ran too rich.

As a test feed the HP pump from the can and run the tank pump into the can and the return to the tank and see what happens to the level.
If what Digger is saying is true the level should drop with out the return going to the can.
This would also tell you if the tank pump is running as it should when the motor is running.

So if you have this switch fixed why did they say with only 1 tank hooked to a 2 tank switch not work?
I thought the fuel pumps moved the switch and being you only have 1 pump running it would work?
May need to plug off the other ports so they don't leak but they should not I would think?
Dave ----

Feb 7, 2021 | 11:53 AM

#17

diggerrigger

Cargo Master

Joined: Sep 2006

Posts: 2,120

Likes: 390

From: Evansville, Indiana

Quote:

Originally Posted by FuzzFace2

What would happen if you were to pinch off the return line with the tank pump supplying the HP pump would it stay running?

This caught my eye. Seems it would allow the required pressure to build. I doubt that any harm would come to the HP pump if this was done only for a short term. EDIT: maybe it might over pressure and rupture the diaphragm in the flow valve.

Another thought. Instead of tank pump to HP pump and flow valve back to the tank, try teeing in the flow valve return into the bypass where the reservoir was removed thus completing the "loop" so the HP pump has access to this fuel. Also, you should probably tee from the same location the return line to the tank. The reservoir check valves would be missing but that might only affect fuel siphoning back when shut off.

Feb 7, 2021 | 12:03 PM

#18

Gorebs9589

Thread Starter

Mountain Pass

Joined: Sep 2019

Posts: 109

Likes: 8

I will try those ideas and if not I will just have to fix it all. But I am curious I understand it may not be getting enough fuel to run but if I prime the pumps a few times if that is the problem wouldn’t it still be able to start and only run for a few seconds but priming the pumps should at least crack it if the lack of the reservoir is the problem. Right?

Feb 7, 2021 | 12:11 PM

#19

KULTULZ

Cargo Master

Joined: Mar 2002

Posts: 3,132

Likes: 219

From: W (BY GOD) V

Quote:

Originally Posted by Gorebs9589

... how can I just make the HP pump pull from the tank? Because as I said earlier I had the truck running for over 10 min strait with just the HP pump pulling gas from a 5gallon can and returning the gas back to another can. Ran very smoothly like this.

Because an electric fuel pump is designed to push fuel, not suck it. The transfer pump supplies the HP pump by pushing fuel out of the tank(s). This was an early design before FORD put the pump in the tank.

As for the return reservoir instead of a full return to the tank, this is mostly a money saving technique. When the HP pump begins to cavitate (for whatever reason), fuel is released/drawn from the reservoir to maintain needed line pressure. The pump is calibrated to not push too much fuel to trip the pressure regulator (in theory).

To have your present HP work on the rail without the tank transfer pump(s), you would have to fashion a gravity drop design where fuel pressure to the pump is generated by gravity.

Best to get a SHOP MANUAL and a pressure gauge and go through the system (IMO).

Last edited by KULTULZ; Feb 7, 2021 at 12:15 PM. Reason: CRS

Feb 7, 2021 | 04:18 PM

#20

Franklin2

Moderator

Joined: Jan 2001

Posts: 56,984

Likes: 2,738

From: Virginia

One other difference between the later HP pumps in the tank and this early two pump system, the early tank systems have the pump in the tank wide open with no baffle systems or anything like that. The later single HP in tank pumps have that plastic "can" around the pump and if you notice, the return does go back inside the can and not into the tank.

I see a lot of these retro EFI systems they have on the market recommend some sort of "fuel matt" to keep their fuel pumps supplied with fuel when using a old wide open style fuel tank.

Feb 8, 2021 | 04:44 PM

#21

Gorebs9589

Thread Starter

Mountain Pass

Joined: Sep 2019

Posts: 109

Likes: 8

Ok so I finally got a chance to look at it today. Weather cleared up. It is not pumping any fuel out of the tank. The pump in the tank is new and is cutting on. You can hear it running but it’s not pumping anything out of it. Any ideas why? I really don’t want to lower the tank again but I’m afraid that’s coming.

Feb 8, 2021 | 04:52 PM

#22

Franklin2

Moderator

Joined: Jan 2001

Posts: 56,984

Likes: 2,738

From: Virginia

Did you get or did they give you the proper sending unit for that tank? The front and rear sending units are different and mount at different angles. And you do have plenty of fuel in it? If it was empty I would put at least 5 gallons in it. I do hate dropping fuel tanks also.

Feb 8, 2021 | 05:29 PM

#23

Gorebs9589

Thread Starter

Mountain Pass

Joined: Sep 2019

Posts: 109

Likes: 8

Update***. It’s running. When I wasn’t getting fuel out of the tank I started tracing stuff. In my tired wore out state I was in the other day I managed to squeeze the hose between the tank and the frame. Once I got that fixed she fired right up and runs great. Thanks for everyone’s help and I’m sure I will be back soon for more help. Lol