Hello,
The switch for going between front and rear fuel tanks on my truck is acting up. It seems to not want to switch between tanks. I was wondering if that switch craps out am I dead in the water or will the truck run off of what ever tank the switch position was in before it died? Same with that valve that goes between tanks if that dies am I screwed or will it keep pulling from which ever tank it was pulling from before it died? I found a used switch on ebay, but does anyone know where to find that valve if I am having a problem with that? Cant seem to find on through LMC or anyone. Thanks for your input

 

Looking at the wiring diagrams, if the switch were totally out of the picture (as in removed), the fuel solenoid would default to one of the two tanks, but it's not clear as to which one. If the switch died, it would not necessarily stay on the one that was last selected. It would depend on how the switch failed specifically. The fuel gauge may or may not point to the correct tank in this case. Stated another way, if the switch dies, there will be a tank connected. So long as both tanks have sufficient fuel, you won't be stranded if the switch fails, but there's no guarantee that the gauge reading is pointing to the correct tank.

The switch is simply a DPDT-style switch, so even if you can't find a factory Ford style switch, you could rig up a less-pretty toggle switch. OR, jump the switch to tie it permanently to one tank until you can find a NOS replacement.

 

I had a '77 F250 that I bought new. It had the dual tanks. I used to run the main tank (rear) dry and switch it to the auxiliary (front) tank. There was a problem with the switch that I never did trace down. Twice when I was running on the aux tank the switch switched back to the empty main tank. So I would suspect the default tank is the main tank. If the switch loses power or, for some other reason craps out, the tank will switch back to the main tank.
I learned to never run the main tank dry, I started to switch tanks when the main got down to about ¼ full. (Before cell phones, if you broke down, you walked ).
Also, the fuel gauge still showed plenty of fuel....in the tank that the switch was set on.

 

First off, before everyone puts the cart before the horse, how exactly do you know it's "not switching between tanks" and that it is "acting up".

These questions need to be answered before any meaningful help can be given.

Dennis

 

I agree tell us a little more about what is wrong, is it just the indicator failing or the actual switch or the valve down by the tank?

Explain exactly what it is doing or not and I am sure fmc400 will tell you the exact way to trouble shoot it, before you start just replacing things.

(78/79 duel fuel tanks frame switch-Duralast/Universal 3 port fuel selector valve used with SW48 toggle switch Part Number: FSV4)

Maybe cleaning some connections and doing a little multimeter work can narrow down the possibilities?

 

I will do my best to explain this the best i can here. The truck is new to me. I had the switch on the rear tank. Actually ran the truck out of gas on that tank, didnt mean to. I put some gas in the tank and best I can tell the gauge is reading correctly. Truck fired up and ran happy. I tried switching to the front tank, gauge went to "E" but kept running fine. (At this time I had no idea how much fuel was actually in the front tank) Switched back to the rear tank truck kept running.
Next day the truck would not start, I was not getting any fuel to the engine. Tried switching between both tanks truck would not start. Tried multiple times switching between tanks, Fuel gauge would not always read gas in the rear tank when i know there was gas in it. Added a few gallons of gas to the front tank, truck fired up and ran. Gauge didnt read fuel level in front tank but only put a few gallons in it so may not of been enough to read on the gauge. Tried switching between tanks again, truck kept running again but did not always read fuel level for rear tank.
At this time im thinking i am just running on the front tank no matter where i put the switch. But i swear just a few days ago it was running off the rear, and now wont go back. Thoughts?

 

Quick troubleshooting ck. Turn key to Run without turning engine on, then, standing outside the truck with knees touching the door sill, switch the lever from one tank to the other with about 15 seconds wait between each action. Do you feel or hear the solenoid moving back and forth. If you have someone to help, get on your hands and knees and feel the solenoid under the cab floor

 

Do you have the valve handle sticking up thru the floor right under the dvrs side seat edge? or you yo have the environmental control panel switch?

 

On the day when the truck would not start how do you know you were not getting fuel to the engine?

Dennis

 

I do not have anything on floor next to the drivers seat. My switch is on/by the heater controls. Is that considered an/the environmental control switch?

 

One of the previous owners has installed an aftermarket fuel filter between the pump and carb. It is one of those clear ones where you can see the filter material inside. When there is fuel I can see it in the filter. When the truck would not start there was no fuel in the filter.

 

Agreed, that's a pretty important question.

 

Manual control selector valve 1973/74 only. The 1973/74 switch only switches the fuel gauge from one tank to the other.

1975/79: D5TZ-9189-B (replaced D5TZ-9189-A, D8TZ-9189-A, D9TZ-9189-A) .. Fuel Tank Selector Valve & Solenoid Assy., located on frame rail.

D5TZ-9A050-A .. Selector Switch ~ Switches the tanks and the fuel gauge.

Both the 1973/74 and 1975/79 switches are located in the heater control panel.

 

Also, that day I was able to get the truck to run for just a bit off starting fluid, so I know it was not an issue with spark.

 

The fuel tank selector valve on my truck is located on the front of my rear tank. Was that a possible location or has it be relocated by a previous owner?

Someone earlier said something about a solenoid under the drivers seat floor boards? I am assuming this is tucked in the frame rail also. Does the selector switch control this or what roll does this play in the system? Possibly were they talking about the selector valve?