I have a 85 Ford F-250 460 4X4, and when I bought the truck used, the rear tank didnt work. I want to fix it and be able to run both tanks, but Im not really sure where to start trouble shooting. Also, does anyone have a wiring digram of the 85? Im going to buy a haynes manual tomorrow. Where should I start troubeshooting, and how can I penpoint the problem. Also, I may need a whole new rear tank because when I bought the truck, the rear tank cap was missing, and I dont know how long the owner ran it like that, so Im not sure if the tank is actually damaged.

 

Sounds like the pump in the rear tank is bad. I would check for voltage at the pump when you turn the key on when switched to the rear tank.

 

Cool, so I should be getting voltage up until the pump with the key on and the rear tank selected, right?

 

No you will only get voltage at selected tank with the key in the start position or with the engine running with oil pressure up.

I have two diagrams, one is for a 1983 and one is for a 1986. I do not know if the 85 is like the 83 or 86.
Her are two the diagrams. You are not going to find them in the manual that you are going to buy.

1986
http://i54.photobucket.com/albums/g91/subford/Fuel/1986460ElFuel.jpg

1983
http://i54.photobucket.com/albums/g91/subford/Fuel/1983FuelElCT-1.gif

 

OK, I'll check it this weekend, does the haynes manual help any with this problem, Im picking one up tomorrow.

 

No it will not, see my post above.

 

Wow! Good info, Thanks!

 

You should get voltage for a couple of seconds each time you turn the key on. This primes the system before cranking. Almost all Fords do this.

 

His system does not work this way and fuel pumps will not come on when you turn on the key. He also does not have a computer (PCM, EEC, and ECM) and that is what turns on the voltage for a couple of seconds on a fuel injected truck. His is not a fuel injected truck.

 

Thats right, I dont have any computer stuff on my truck. With that in mind, whats the best way to start troubleshooting it??? This is my next repair and I want to get started on it by this, or next weekend coming.

 

It could be the valve, I think its under the cab on the frame rail on this truck, or could be wiring, switch or both, you should hear a faint click when switching tanks if the valve is working

 

With this fuel system and the age of your truck it has more than likely been worked on by a lot of people that did not understand this fuel system.

As a result they may have bypassed some of the safety items in it like the oil pressure switch and may have removed some wiring like the wire from the Starter solenoid to the system. The wiring to the rear fuel tank may have also been removed.
So it hard to tell you what is what with out knowing what has been done to the truck.

So if the oil pressure switch is bypassed then you would have power to the system as soon as you turn on the key if the Inertia Fuel Cutoff switch is OK.

So this is a good place to start, take the wires off the oil pressure switch and short them together and I would also take the + wire off the Ignition coil and unplug the Ignition Module.

Now turn on the key and start tracing power back to the tanks and see if the fuel selector valves motor runs by having someone change tanks while you feel the fuel selector valve motor or check it with the test light.

Always use a test light to trace power back to the tanks and not a meter as the meter will sometimes give false readings and you will think you have power when you do not. The meter will not load the circuit and the test light will.

And of course if you have any questions at all just PM, email me or post them.

 

Cool, I'll try some of this this weekend, Keep your PM on!!!...lol