I have a 95 f150 that has twin tanks. Rear tank "hums" at the turn of the key. If I turn the truck off, switch to the front, no "hum" is heard. While running, If I switch from back to front, the gas guage goes to "E" and I have to switch to the rear tank. The front tank is full.

I have been reading the threads and will go back and consult the repair manual again.

Any comments/fixes welcome.

 

Sounds like my Truck 92F150-4x4.back tank u can here ft pump u did not hear .When switch over to ft pump it ran ,but poorly and put return gas in rear tank ,causing it to come out of the cap and spill every were. In staled new ft pump new switch. new press reg. still returns to rear tank. Just got a new rear pump have not had a chance to install as yet, as far as i know we have the same system as trucks did not change Till 97.sound like were in same boat or P.U. Will post my findings when i put rear pump in ,also did all filters and tank switch.nothing left to replace at this point. Also i found odd i had my truck on my lift with ft return line disconnected with a hose attached and in a bucket and no fuel came out with truck running, DO Not suggest any 1 do this !

 

I replaced the rear FDM with a Bosch unit, lifetime guarantee from Advance for $148 plus tax here in SC (the strainer comes with it) and instead of the front tank filling the rear tank, the rear tank started filling the front tank. I replaced the pressure regulator, $46 from Advance tonight and didn't notice any further cross filling, but I'll drive it tomorrow and see and report back. I let the bed back down and put three nuts back on and put the back bumper back on with two bolts for easy access. Taking the bed loose and lifting it on the passenger side is the way to go, especially if you have to go back in to change the other pump or have a leak.

I checked the Haynes manual, and it says the "shuttle valve" in each pump also allows the recirculating fuel back into the correct tank, so that's a further complication.

 

When you say pressure regulator, is that the fuel pressure regulator in the engine bay that you replaced? Curious? I hope that was the fix? Good luck


Mario

 

I took the old rear FDM (pump) apart tonight to try to see how it APPEARS to work. The plastic case has a wafer check valve in the bottom of it to feed the case and the enclosed pump from the tank. The pump when it is on actuates a diaphragm that unseats a plunger sealed by an o-ring to let the recirculating gas from the injectors back into the tank that it came from (which is the pump that is running). The pump itself has a ball check in its inlet and a possible wafer check feeding the pump rotor. If some of the above wears out or goes wrong, the other pump can back feed through it. Even if we rarely used one of the pumps, it could still go bad. So, it's likely that if one pump is bad and the truck has a lot of miles on it, the other pump is headed that way, too. And, if the pressure regulator goes bad and sends too much pressure back to the pumps, it could unseat the unused pump check valve and fill that tank, from the other tank. Crap shoot.

 

So you are basically saying if you replace one pump you might as wheel replace them both... Could you take some pics of this stuff. im curious


Thanks
Mario

 

I'd still try replacing the offending pump first and see what happens, unless you just don't want to deal with it again (hopefully) and go ahead and replace both pumps and the regulator. Especially if you raise the bed on one side like I did and its all there in front of you, except for the regulator, which is an easy swap under the hood.

The offending pump is the one that is in the tank being filled from the other tank.

I don't have picture capability, and its all back together now anyway and the old pumps thrown away.

 

Hi Guys it took me along time to change out rear pump.Just fin. a while ago i put in new rear pump same co. as ft pump .All is well no more pumping gas to rear tank .Truck Runs great on FT.or Rear pump. any body else out there having these same trouble .do your self a faver and buy 2 new pumps and be done .1990 and up that is .Thanks to all who help out with advice .KiloG69

 

My truck does the same thing and I need to do this, but I have an idea for another fix and wonder what everyone thinks. Would it be possible to swap in a physical valve like the older trucks had. Somehow wire it in to the pump harness to actuate it. Sounds like a guaranteed fix, but I don't know if it's feasible.

 

I have a customers 1994 f-150 2wd 6cyl. with the same probs, it pumps the front tank into the rear. I found this *click*Ford E*link*
Was wondering if this item is on anybodies truck?

Also here: https://www.ford-trucks.com/forums/6...tor-valve.html

But this may be specific to 1986-1990.

 

To kentucy red neck, I have spent many hours under my 92 F150, the return line can be made to work with a valve if u what to go thru the pain ,i thought of that right off the bat.when my trouble started .I had a old dodge that had a ball valve with a handel to switch tanks. If u are in a 90 and later PU. U have 2 high press pumps with valves in them..I just fixed mine today ,by putting in new rear pump.TO 87CREW Daully That switch modual is 89, and down. they had 3 pumps one low press in each tank 1 switch modualls. u have in pic. and 1 high pressuse on frame for the injectors.This has been a learning experence for me .I am very thank full For all the feed back from all folks having these same troubles on the diffrent year fords. Hope i was of some help.

 

The problem with a manual valve would be having the return gas go back to the tank it came from. There would have to be two valves, one for the supply and one for the return. You could always block the lines to the tank that's getting filled, and use the other tank by itself, if the return check valve it that tank is still good. Mine wasn't, and the system lost pressure when I turned it off, and had to wind the starter to start it back up. It's fine, now that I replaced both pumps and the regulator - $370 for the parts at Advance. For ktmcgn39: my back pump hums, too, but it has to do with the spare tire up against the tank.