fuel pumping to back tank while driving

[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

 

[blacksnapon]

Its the tank switching valve on the side of the frame, driver side, about halfway up.

 

[rjrgta]

switching valve

Thanks for the reply.

I see one fuel line manifold in the frame beside the front tank. The lines going into and out are a hard fit, no disconnects. No wires or electrical to this part.
Lines disconnect forward and aft of this manifold. I don't see anywhere else the lines come together. The lines from the front tank come down and join the lines going from the bank tank to the motor.
So is this little 1 in. long line junction the tank switching valve, and if so what controls it ? This looks like it has no parts inside, just a junction.

Is the tank switching valve an electric operated valve ? Only wires I can see disappear to the top of the tanks and are plugged in to the injector manifold connectors.
My Chilton manuals don't even mention it. I can't find this valve.

Randy