Fuel Tank Selector Switch Questions

[dynoh2o]

I have an 83 F250 6.9L that will not switch tanks. It is stuck on the front and will not register on the gauge either. I was messing withe the switch and blew the aux fuel circuit fuse, no big deal. I have driven the truck since then and it still runs, on the front tank I am assuming. I really need a more detailed wiring diagram of the fuel system because I can't see from the ones I have how the heck the front tank fuel pump can be running with the selector circuit un-powered. Any help is appreciated.

 

[IDIoit]

welcome to the forum.
theres 2 fuel pumps on these trucks.
1 a low pressure mechanical lift pump, on the passenger side front of the engine, and a Injection Pump on top.
these tanks do not have separate fuel pumps.

 

[dynoh2o]

Thanks, answers a lot. So all the selector switch does is switch the aux fuel valve? It would be nice to find a diagram of that

 

[IDIoit]

use the search, there are a few on here. the FSV are kinda pricey, but cure alot of issues. including fuel levels.
you can modify it if you want, i myself i have bought the almost 300 dollar direct swap and was done, didnt have to F with it, and on my current truck, i deleted the front tank all together, and ran a 33 gal rear tank
anything can be done.

 

[OLDBULL8]

Rarely does the actual switchgo bad. here is a wiring diagram of the FSV. You could have corroded pins on the connector or a broken wire.

Azone, O'reilies, Advance all carry the Pollack style FSV, it is not a direct fit, if you have the Ford Quick connectors for the fuel lines, and it may mount horizontal verses Verticle, but it is awhole lot less expensive, ~$80. Just ask for the Fuel Selector Valve. If you get one there you need the new connector harness.

Do you have a vacuum on the rear tank when you pull the filler cap off? You either have a venting fill cap or the tank vent hose is plugged.
Sometimes the shower head falls off the pickup in the tank and you can't get fuel if your below a 1/4 tank.
You should hear the FSV switch if it isn't stuck. Tank connecting hose will disintegrate inside and debris will get in the FSV and stick it.

 

[madpogue]

Here's from the 1985 EVTM - http://userpages.chorus.net/elephant/FuelTankSelector1985.pdf .

 

[dynoh2o]

Thanks much

 

[jim_22]

It is a sophisticated switch. When you switch it, it powers the valve into the new state and stays there even if power is removed until it is switched again.

 

[dynoh2o]

Thanks, with the help of a correct wiring diagram, thank you madpogue, I see that the valve is a motor actuated valve that uses reversing the polarity to move between positions. That explains the ground terminal in the switch wire harness. I reconnected the switch and will check the tank valve terminals in the morning. Hopefully they just need cleaning.

 

[madpogue]

I was able to test one using a small 12V SLA battery and a couple jumper wires, connected to the terminals associated with the orange and brown wires. I could connect them to the battery terminals one way, and it would switch once and stop. Reverse the polarity of the battery connections, and it would switch back. Using a piece of hose and blowing into each port, I was able to confirm that it was opening/closing the proper ports with each activation.

 

[IDIoit]

I was able to test one using a small 12V SLA battery and a couple jumper wires, connected to the terminals associated with the orange and brown wires. I could connect them to the battery terminals one way, and it would switch once and stop. Reverse the polarity of the battery connections, and it would switch back. Using a piece of hose and blowing into each port, I was able to confirm that it was opening/closing the proper ports with each activation.

was that the one i sent ya a while back?

 

[madpogue]

No, this is a FSV I bought from a junkyard in Pocatello. Works, but it's marked "GASOLINE", and the port arrangement is like the "generic" Pollak valves, all tank ports pointing down, instead of the rear tank ports pointing aft. Just the thing I wanted to avoid, oh well I got it on the cheap.

 

[dynoh2o]

OK fellow forum users, here is an update on my issues. I crawled under the truck and located the six port valve. It was caked over with thirty plus years of crud. I cleaned enough off to access the wire plug going into the valve, removed it from the valve and found that the female part looked to be contaminated with diesel fuel. The plug on the valve is dry, but it looks like diesel has migrated up the wiring from somewhere. I don't see any obvious leaks, but you know diesel, it can get into anything from even a small seep.

Anyway, I checked the voltage at the female plug and had the correct voltage and polarity for the dash switch position. My next move is to get some decent cleaner/degreaser (kind of hard to do in the peoples republic of California) and clean the entire valve and electrical connections and then check the valve operation again.

Thanks to all of you for your input