I am currently running with the front tank and have no problems. But my new front tank is not here yet and as the old one leaks about a gallon a day I need to be able to use the back one in the mean time. I have never owned a truck with dual tanks before and am not sure where to start looking for the problem.

 

After I read some other posts I went outside and checked the fuel level. The tank is FULL and not just by the gage.

 

Pre-Power Stroke Diesel (7.3L IDI & 6.9L) - Ford Truck Enthusiasts Forums Here is a link to the page for your engine, probably better if you post the problem there for the experts.
However when you use the tank change-over switch on the dash it should operate a tank selector valve to cvonnect the fuel lift pump from one tank to the other. My guess would be that the selector valve is not working. Maybe bad switch, maybe bad valve, maybe bad wiring, maybe bad fuse.
Anyway ask the guys on that other page.
Good luck.

 

Thank You soo much this is all new to me and I'm still trying to figure it out. Thenk you

 

Ford Truck Enthusiasts Forums - Cruickie's Album: Service and repair images - Picture Here is a link to a wiring diagram. Yours should be similar.
You could check that you have power to the switch and valve and that the fuse is good.

 

Get the next grade up of Diesel.....

 

Thanks Guys

 

Today is the first day I have gotten to get outside. It's been raining for a week-10". But I'm begining to think this is gonna be a stupid simple fix. I just went out an put a couple gal of fuel in her and she fired right up So I drove her to my buddy's and on monday we're gonna start replacing everything from the selector valve back. now that I'm home I'm begining to wonder... What would cause her to just fire up like that? mabye a sediment issue somewhere? is there a safty switch that wont run the pumps if the tank is empty? or is this operator error?(smart a$$ answers will be acceptable) BUT if you can't take it..don't dish it out C-ya

 

The fuel pump is mechanical, driven by the engine, so it has no way of knowing if the tank is empty or full.
A common problem with these trucks is that the fuel pickup tube in the tank can crack/break, usually at around the quarter full point causing the pump to suck air when the fuel level reaches that point. That could well be the problem. Although not with a full tank.

 

I just ordered two new complete sending unit assemblies for my tanks. I'm gonna replace thoses while I'm in there just to rule out any and all fuel pickup problems. I am in agreeance with you on the pickup, its just too wierd. this is driving me crazy. I am not gonna have any confidence hauling with this truck unless I restore the fuel system. And I did check,and the fuel delivery components on the motor plus the glow plugs were just replaced last year. So I just need to replace everything behind the fuel pump. If I'm forgetting somthing or somebody has somthing I need to check please let me know. right now the list is as follows: fuel lines,selector valve,tanks,fuel sending unit/pickup assembly.

 

I am really impressed by the way. Not one person has asked or suggested that I might have flooded it. I can take it guys. Did I just flood the darn thing?