Got a 94 F250. 5.8 gasser
Couple of months back the rear tank wouldnt show fuel level. (I was living with the situation till the spring)

Anyway I was plowing this storm and the front tank started not showing fuel level. truck ran out of gas even though I though I had at least 1/4 tank in rear.

Fill front w/ gas can (less than half gallon) and barely get to station.
At the station, went to fill rear and the nozzle kept clicking so I went to the front. the front tank filled up no problem. Went to fill the rear again and it wouldnt let me. (The nozzle kept clicking off (like when the tank is full). I kept trying to filli the rear thinking maybe theres a check ball in the fill and it was stuck. Barely got a gallon and when I pulled the nozzle out the fuel started coming out of the fill as if it was full. OK I thought, I'll tackle this in the spring too, at least I got one tank.

Kept plowing but now the truck would cut out every now and then, like someone shut the gas off. Most of the time while i was driving it would come right back on. Through the night it got worse and I noticed it more while being in reverse.
At idle, I would have to restart it.
A couple of times I would switch to the rear tank and it would just die.

So I be replacing both fuel pumps?
On the fuel level, I was hoping to get a way with just replacing the float?

 

Sounds like you have at least one fuel pump out and a bad sender in the rear. I would get a pump-sender-float set up for the rear tank ($150ish at RockAuto Auto Parts). Keep in mind the easiest way to replace these is to remove your bed... Get the rear fixed and do a test drive to see if that fixes your problem because you at least have to replace your float and/or sender. if that doesn't seem to quell the problems you might have other problems further up besides the pumps and sending units. Because they are kinda spendy I wouldn't buy both right away until you know the problem is solved after installing the rear unit.

 

Also sounds like you may have the fuel transfer problem where the front tank is pumping fuel into the rear and overflowing it as you drive(if gas milage is really bad that is why). The fix for this is to replace the fuel delivery module(canister that contains the actual fuel pump + check valves) in the rear tank, also be sure to fit new fuel level senders when you change out the FDM.

 

check where the wiring harness for the rear tank goes onto the sending unit. i had a simmilar issue,the plug that goes on the tank had come off and was dangling. when i was trying to run off the rear tank the high pressure pump on the frame was pulling fuel from the front tank due to the rear in tank pump not working and returning the fuel to the rear tank. it would stall when first trying to switch tanks to the rear tank.

 

Does it come as a complete assembly?

Conanski, Fuel mileage was alway bad for the last two years, average of 8mpg.

"also be sure to fit new fuel level senders when you change out the FDM. " Can you explain more.......how do i "fit" it?

fdude64....I'm gonna try and look as soon as the snow makes it possible.
Wouldnt that be great if it was such an easy fix. A man can dream!!

 

Well, I played with the truck alittle. (hard to do on the side of a highway)

The switch to select fuel tanks had 5.8v to it. The headlight switch had 11.9v.
Check all fuses. All good. swapped relays......truck still wont start.
Put a test light to fuel pump terminals and only one termial had 12v.

Truck still wont start.... wants to but doesnt.

Jumped the middle wires on the switch to 12v supply and still wont start?

Bad pumps?????
Did I burn something up jumping the switch?

Towed it home and checked the shrader valve on the fuel rail and no gas.

 

Anybody got a wiring schematic for the fuel pump circuit??

 

I don't recall the setup of a 94 dual tank, it is probably close to my 90 which does not use an electrically operated mechanical switchover like the 87-89's did.

I think the problem you are having is low fuel pressure. On my truck it was the front tank that had the problems, it would run from it, but ran better from the rear, had the crossflow problem when running from rear it would fill the front to the point it was spilling out the vent to the charcoal can under the hood and then to the ground.

I replaced the front pump hoping to fix all problems, new pump check valves work great, I no longer have the crossflow problem, but running on the front tank is not great and it will not start on the front tank with new pump. Rear working well. I put a pressure tester on the fuel rail, I would get the correct 60 or so PSI from the rear pump, but the front would only give me about 18-24 PSI. What I believe the problem is that the rear pump check valves are also failing and not closing on the fuel feed side [unlike the failed front one that was problematic on the return side] so it is not allowing the PSI to build to what it should be to run and start the engine, and is possibly dumping the fuel into the rear tank also.

As for the fuel gauge issue, could be just the float, they are brass cans, mine had a pinhole in it where the steel wire that holds it in place from the sender arm wore through and let it fill with gas and always show empty ... $5 replacement when changing the pump assy if that is it.

 

Check out this thread: https://www.ford-trucks.com/forums/9...4-9l-f150.html in Post#2 Bill has some excellent photos and schematics that should be applicable to your truck.

 

wait, if the rear tank wont take fuel. the filler is a dual tube system. there is a 2 inch hose in the middle and the outer is the vent . my bet is the center fill tube came off. i had this happen on my mid tank on the 96

 

F...in Ford engineers couldnt find better spots for the bed bolts????

anyway, I took the bed off so that I have free and clear access to the tanks, wiring and hoses.

Funny though when I took the bed off, gas came puring out of the rear fill neck. (Dont know if its becasue it was under pressure or what). No issue with the front. about 1/2 gallon or so.

Quick check of the front tank plug and I was not getting 12v at the plug.

Raining this week so I'm gonna troubleshoot more this weekend.

 

i had the same fuel problem on my 96 250, i didnt pull the bed, i dropped both tanks an replaced both FDM's, and it wasnt cheap

 

I figured working from above is easier than from below. Especially with gas.
Plus I have to "tweak" the bed.

When you say FDM's, do you mean the fuel pump/float assembly in each tank?

Is there a check valve in between both tanks?

 

When you say FDM's, do you mean the fuel pump/float assembly in each tank?.

yes



Is there a check valve in between both tanks?[/quote]

not sure, all i know is, i changed everything an never had a problem since

 

theres a check valve in the internal passage of the pump body inside the tank. thus the reason its safer to pony up and buy the oe pumps