I've got the dual gas tanks no my truck and my front gas tank has a bad fuel pump (I think, there's no power in the upper rpm's so that's fuel pump) and I've noticed that it's never ending. I've been going on it for about 2 weeks now. Off and on, like around the city I'll use it cause I want to burn the gas out of it to fix it. But it seems like whenever I use it, the guage barely moves. It moves but slower than the rear tank. I've put $10 in it a long time ago and I just started using it like 2 weeks ago. And I use it alot, only around the city like I said.

When I use my gas tank in the rear $15 CAN get's me like 2 days!
So somthing is up with the fuel system. I can't drive for very long on the rear tank but the front tank is neverending....what does this mean?!?!

 

I don't know what it means, but I wish I had your problem.

 

My '96 did the same thing. Each tank has its' own return line. In theory, the unused fuel is supposed to return to that tank. But mine always returned to the side tank when I burned off the rear. That could be what you're seeing. You may just have to run the side tank down with the pump or drain it. If you can get it down to at least a 1/4 of the tank, you can just loosen the straps and get to the pump without pulling the tank.

 

It sounds like you have a bad check valve on the pump in your front tank. I have this same situation, but I noticed mine after I had both tanks full and was running off the rear tank first. The unused fuel is supposed to flow back into the rear tank, but instead it was allowed into the front tank by the faulty check valve and ended up overflowing out the filler tube.

There was a recall from Ford, but it had expired on my '90 F350. Until I get around to replacing the front fuel pump, I simply run the front tank first then switch over to the rear tank.

There has been a lot of discussion on the topic if you want to search the archives. Good luck.

Pat

 

yea the back tank goes faster because it dumps fuel into the front one. i go about 250 miles on the front tank, 100 on the rear, and then another 100 on the front. thats with hitting the switch at 1/4 tank. always use the front tank first so it doesn't overflow.

 

Well that sounds like a bad problem, but I thought that was only for the late 80's and ealy 90's trucks. Guess not. whatever it is I think I'm getting some sweet fuel milage. It's pretty sweet being able to go all around town and not have the gauge even move a bit. So what should I do? If I replace the pump then what will happen? Will I go back to burnin' fuel really bad? Cause it's brutal $15 is like 20 litres and that get's my like nothing. No where! Maybe to town and back twice and that's like 30 KM tops.

So your saying that when I switch tanks from the back to the front that my fuel is sloshing back and forth between tanks? Cause I thought they were on seperate lines? I'm confused?!?!?!

 

Changing the pump is not going to correct your problem. The fuel is returned to the tank by the DFR(DualFuntionReservoir) relative to switch position. This is where all the valves that control the flow is. It's mechanical not electric. It also has an internal filter.
Vehicles with dual tanks have three electric fuel pumps. Two low pressure in-tank fuel pumps, located in both the front and rear tanks, pump fuel into a reservoir. A high pressure in-line fuel pump then takes the fuel from the reservoir to the fuel injectors. This system can draw fuel from either the front or rear fuel tank unit. With the ignition switch in START or RUN, current flows through a fuse link to the fuel pump relay. The dual function reservoir replaces the six port selector valve on fuel injected dual tank vehicles. The dual function reservoir switches the tank from which the engine draws fuel mechanically, instead of electrically.
The dual function reservoir operates as follows:
Fuel pressure created by the selected in-tank fuel pump exerts force on a 3 inch fluorosilicon diaphragm which is in turn connected to a T-bar and two shafts. This force moves the valve shaft, simultaneously opening and closing supply and return ports. When the alternate fuel tank is selected, pressure is exerted on the opposite side of the diaphragm, moving the valve shafts to open the alternate fuel tank ports.

 

I checked at the local parts stores to try and find a filter for this thing. I was going to tear it apart and clean it up and replace the filter. They weren't able to find a P/N for it. From what I can tell, this thing is unservicable and you have to replace it. $70 from Ford.

 

So your saying that when I switch tanks from the back to the front that my fuel is sloshing back and forth between tanks? Cause I thought they were on seperate lines? I'm confused?!?!?!

From my diagrams, there is a diaphram on the top of the resovoir. The only way I can see fuel getting to the front tank is if there is a hole or a tear in it to allow fuel to flow to the side tank. The tanks are not directly connected to each other, so there is no flow from one tank to the other.

 

This is interesting. So I have 3 fuel pumps? The resevior things sounds really dumb. Why not just pump the fuel from one tank to the injectors? And if you use the rear tank just pump the gas from the rear tank to the injectors?!?!? That would be the logical explanation. Well I'm fixing this then. I'll put in a new fuel pump and that's about it. This is beyond me and it's design is really stupid almost as stupid as trying to replace the corner light bulbs on the headlights. I want a new truck anywho. Maybe another ford or maybe something else.

Is the resevior called a pressure resevior? There wouldn't be much pressure in the tank now would there? So it would go to another resevior where it would buildup some pressure and then get fed thru the lines? Well what is the fuel rail for then? I guess it's beyond me and I can't understand this. Sorry guys.

I just think I'm getting better gas milage than I really am. Oh well. I'm gonna put in $5 and see how far that gets me. Any more help would be appriciated. Thanks.

 

If you're not having any problem with the system other than high fuel level in side tank, I would'nt even change the pump. Just run on the front and when it gets low, just switch to the rear. I never changed mine. I would change the high pressure pump on the frame first. Check your fuel pressure at the rail.

 

The pumps in the tank are low pressure, which feed the reservoir. The reservoir provides a constant fuel supply to the frame mounted high pressure pump, mosty for any unusual attitudes the truck may encounter. The high pressure fuel then goes to the regulator on the back of the rail which supplies fuel to the injectors as the engine requires it. It is at this point unused fuel returns to the tank via the DFR.

 

So from your description, Loos, it sounds like Moose has a bad DFR and it is sending returned fuel back to the side tank whenever it wants instead of sending it to the tank being used? So simply replacing the DFR should solve Moose's problem and his truck's fuel return system will be returning his fuel back to the correct tank at the correct time and his 'observed' fuel usage from each tank will return to normal?

 

From the diagram of the DFR, correct. Ford had a recall on these. It's the only way I see fuel being able to return to the side tank. I wish I was able to post a picture of this thing.

 

exactly. i think alot of us have this problem and thats the easiest solution. i dont understand how somebody can find it complicated. fuel in rear tank dumps into front tank, refilling it. thats why it is never ending. its not a difficult concept. use front tank, then rear tank, then front tank again.