fuel pumping into both tanks problem

[rjrgta]

Hey guys, I'm new to the site, driving nothing but Ford and Mercs for 30 yrs.
My work truck is a 93 F 150 with the straight 6 and 5 spd. man. trans.
For the past 6 months somethings been wrong with some kind of fuel switch somewhere. I fill up the front tank and drive on it, fuel is pumping to the motor and into the back tank at the same time. When I get down to about 1/4 tank in front, I switch to the back tank and it's 1/3 full. I drive on it till it runs out, then back to the front till it gets low, to the back till it's empty, then to the front till fill up time. I found this out using only the front tank for a long time, I got to smelling gas pretty strong when I was at the back of the truck. Getting under to look, I see the back tank is leaking fuel somewhere from the top. Thought maybe I had absentmindedly filled up the back last fuel stop.
No. Fuel was being pumped in the back tank while driving and it was over full and running over.
I've been through my repair manual and through the subjects here and don't see anything that would tell what part is not working right.
Does anybody here know what this is, what part needs fixed/replaced ?
Thanks,
Randy

 

[Marsh N Sons]

Not for sure. as it hasn't happened to me.
But when I bought my truck, the owner at the time said he was having the same problem as you stated. The intank fuel pump wasn't working, so he just cut the line and plugged it.
I still need to replace the pump, but don't know what I'm doing just yet.
I'm no mechanic, but it seems you have the same issue he did.
Marsh

 

[5.0Flareside]

Im not 100% on the fix but I think it has something to do with a check valve..

 

[kiwi f150]

You need one of these http://www.rockauto.com/catalog/moreinfo.php?pk=293230&cc=1122084 - i would say your front Fuel delivery module has gone bad .... more specifically the check valve in it has stuck and while it is still supplying fuel to the engine the return line is still switched to the rear tank causing it to overflow.

 

[Fellro]

It is the fuel selector valve. They commonly do this when they fail. Mine decided to just leak... Since the truck doesn't go all that far, I just bypassed the valve using a piece of 3/8" and 5/16" pipe to make the connection without having to cut the hoses or anything. That way if I want to put it back, I can.

 

[Alvin in AZ]

My '90 and '91 parts trucks had two tanks and have a stainless steel one-
way valve right on the fuet tank "pipe'. They are a bugger to get loose,
Ford got carried away with the "quick connect" fitting on 'em.

Anyway, I'm wondering if 92's and up have those?

It's for sure (on those two trucks) to help (or make?) the running fuel pump
to pump toward the engine and not into the other tank.

Tried a few different types of "quick connect" disconnect-tools and this
type was the first one to actually work...

...the blue one doesn't have a factional inch size, just a number, it's the
most useful one on my two parts trucks and '91 Bronco.

I modified all of 'em tho. Clamped 'em in the vice with whatever size hunk
of steel they needed to hold them round and counter suck 'em a little bit,
that helped 'em work and made it so I didn't have to go buy another type
of tool.

The blue one works great at disconnecting the throttle cable from the
gas pedal too, BTW. LOL

Alvin in AZ
ps-
Now that you know what the tool I used looks like... The one-way valve is
so close the the bend in the steel tubing that I had to take the tool apart
and insert it one half at a time. Anyway, I bet a guy could get a couple of
those things from the wreckin' yard for cheap.

 

[rjrgta]

Guys,
Thanks for the replys. I found an extensive thread on the Ford Truck Enthusiast website about this particular problem. You can check it out at this link; http://www.ford-trucks.com/forums/896513-fuel-pump-or-tank-selector-valve.html

The guy is adamant that the tank that is being filled has the bad FDM (fuel delivery module) or fuel pump. You would think just the opposite but it's clarified there several times.

I'm going with replacing the rear pump. There is no external fuel selector valve in this year range, as I gather from the thread and I sure don't see one on mine.

Thanks all.
Randy

 

[Fellro]

I had forgotten the 92 had the check valves in the lines like Alvin mentioned.

The pump itself has nothing to do with the return, only the supply.