Hi all, could ya help me out? My husband hates computers so please bear with me while I ask for advice. I have a 1981 Ford F250, 6cyl, gasoline not diesel, granny 4 speed, dual tanks. anywho.... The Fuel Switch isnt switching to the bottom tank. Up on the dash it will read how much is in each tank when you switch it, but bottom tank wont work. Top selonoid has fire, but the bottom tank has no fire. That's the only thing my husband can figure out what is wrong. Can anyone here help us with this? I am tired of being stranded on the side of the road. Thanks

 

In a 1981 truck, I can't imagine you'd have electric fuel pumps in the tanks unless some
other owner added 'em; instead, you should have a mechanical fuel pump. However, I've
heard of some six-bangers that *did* have that, yours might be one of them.

Assuming non-electric fuel pumps, I see three possibilities:

1) The tank-switching switch is bad (doubtful but possible).

2) The tank selector valve is bad - the thing mounted on the frame that chooses from which
tank the gasoline is pulled (they go bad but I've never experienced that).

3) The fuel tank sending unit has gone bad, and it's lying to you about the quantity of
gasoline in the tank (VERY common). Try adding a gallon or two of gas to the tank and see
if things are better for your husband; if so, replace the sender (rockauto.com, y2kfordparts).

 

what i would do is crawl under the truck,drivers side under the cab infront of the front tank.check to see if it is rusty(maybe a bad ground).use a test light find a good clean ground and see if you have power to the wire,if yes the valve could be bad or have rust on the frame causing a bad ground.this was the problem on mine.a new valve is under $50.00 if the valve is bad.i just cleaned the frame and the mounting tab,use lots of die electric grease and tightened it up and no problems.let us know what happens.BTW welcome to the site.

 

Thanks guys for your comments, below are some more info might help.

mechanical fuel pump on side of motor
When my husband chect the switch for the tanks on the dash. The Front tank is real bright, but the back tank flickers.
No rust
Okay lets see if I can communicate these instructions. This is for the wires on the fuel tank switch on the dash. Testing with test light.

Red wire stays bright light at all times
Brown wire Nothing on top tank, flickers on back tank.
Two yellow wires nothing on top tank, flickers on back tank.
other wire (couldnt remember color) Bright light on front, back tank nothing.
__________________________________________________ ___________
Imangine this is box with wires please disregard the !!!. I couldnt get the positions of the wires right, without using the !!!

! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *Brown Wire (ground????)


! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *Red Wire
*Yellow Wire


*Yellow wire !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *other wire (front tank???)

 

Quote:

Originally Posted by 1981FordF250 Granny

When my husband chect the switch for the tanks on the dash. The Front tank is real bright, but the back tank flickers.
No rust
Okay lets see if I can communicate these instructions. This is for the wires on the fuel tank switch on the dash. Testing with test light.

Red wire stays bright light at all times
Brown wire Nothing on top tank, flickers on back tank.
Two yellow wires nothing on top tank, flickers on back tank.
other wire (couldnt remember color) Bright light on front, back tank nothing.
__________________________________________________ ___________
Imangine this is box with wires please disregard the !!!. I couldnt get the positions of the wires right, without using the !!!

! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *Brown Wire (ground????)


! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *Red Wire
*Yellow Wire


*Yellow wire !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *other wire (front tank???)

My 1981 wiring diagram shows 5 wires going to the switch...

The red wire goes to the fuse panel and provides power to the switch, it makes
sense that it's always hot.

Yellow/white stripe leads to the dash gauge.

Dark blue/yellow stripe goes to the side-mounted tank's sending unit.

Yellow/light blue hash goes to the rear tank's sending unit.

Brown/white stripe goes to the tank selector solenoid mounted on the frame
underneath (near the side tank).

Here's a test... with the key in ON or ACC,

1) remove the wire from the side tank's sender and ground it out; the dash
needle should swing all the way in one direction (I forget if it'll be full or
empty).

2) Replace that wire, do the same test on the rear tank.

If those tests pass, the wiring from the tanks to the dash gauge is good (as is
the gauge). I know you don't have questions about that but it's a way to
confirm or deny things.

The fact that the brown wire doesn't get any power on the top tank sounds OK
to me. But, the fact that it's flickering when trying to send power to the other
tank is most likely your problem. I can think of two or three possible reasons....

- The switch is bad.
- The solenoid in the valve itself (underneath, on the frame) has a bad ground
or is bad in itself.
- Bad/corroded/broken brown/white stripe wiring between the switch &
solenoid.

I will ask a really good 1981 guy to offer his diagnosis & opinion....

 

Here is a link to a scan of the wiring diagram with the fuel selector switch, the area your
husband is concerned with is around B-9.

http://img15.imageshack.us/img15/6562/pg3halfsize.gif

It's pretty big, make sure your browser doesn't shrink images to fit your screen.

 

Being that it has a mechanical fuel pump, and the gauge "is" switching, id have to guess that there is a clog someplace either in the switching valve or the line to the rear tank or the rear sending unit strainer. If the switching valve is clogged you maybe able to clean it out instead of replacing it. In my 85 with the 6 port valve the fuel gauges will not switch unless the valve successfully switches, however that only means the switch is getting power and the the mechanism inside is sliding back and forth not necessarily that the valve is functioning. As for the flickering test light, the wires that run to the tank sending units are suppose to blink those are the fuel gauge wires. If you have erratic flickering of any of the wires then you have wires rubbing someplace and are about to shortout.

 

The 1981 only has a 3 port selector valve on the frame.

The Brown wire powers the 3 port selector valve on the frame.

If you notice in the diagram that Ctubutis posted, the fuel selector valve in the diagram is switched to the aft tank.

Denergized the selector valve passes fuel from the Aft tank to engine.

Energized, the selector valve passes fuel from the mid tank to engine.

It sounds like the fuel lines on your selector valve is hooked up backwards from the tanks, or at least it seems that way according to the diagram. Make sure that when you have the switch on the front tank, that it's actually drawing fuel from the front tank.

-------------------------

The flickering on the brown wire is your problem.

Take your test light under the truck to the Fuel tank selector valve, and unplug the brown wire from it. Plug in your test light to it, and ground the other end. Have someone flip the switch on the inside.The test lamp should glow bright on the front tank, and be off on the rear tank, according to the diagram. If it works backwards, this is fine, just make sure the fuel lines to the valve is hooked up correctly.

If you get a bright test light in one of the tank modes, but not the other, with the test light hooked up, your selector valve is suspect. The selector valve grounds to the frame, make sure that ground is clean. Remove the selector valve and sand the mount, and the frame, so clean metal can touch each other. Dielectric grease will prevent rust. If it still doesn't function, replace the valve.

If the test light flickers as before, then the dash switch is bad, or the brown wire leading to the switch has a short. Unplug the fuel selector switch in the cab, and take a piece of jumper wire, and jump the Red and brown wires together at the connector. Then with the test lamp hooked up under the truck at the selector valve's brown wire as before, the lamp should be brightly lit now. If it is, then replace the dash switch. If it still flickers, repair the short in the brown wire between the selector switch and selector valve.

Hope this helps.