Rear fuel tank issues

[jmadigan]

New here to the forum heres a little background to the truck. I have a 1983 f250 with the 460 4 speed 4x4 i purchased it a few months ago. I have had a few problems with it that ive been able to figure out but this one is stumping me. I cant for the life of me get the rear tank to pump gas. It has electronic in tank pumps i pulled the rear tank and found that the fuel line on the pump was eaten away and tank was full of debris. I installed a new airtex pump and sending unit went to go test the rear and it still wont work. I put about 4 gallons to test it but my fuel pressure gauge reads 0 and it dies. The fuel level gauge goes up past full so i went to the selector switch. Bought a new switch the pigtail is not the same and i cant seem to find the right one. The one that is in the truck has a 6 prong rectangular pigtail and the switch has 4 terminals. The replacement was a 5 terminal trapezoid pigtail. The fuel pumps and switch seem to be controlled by 2 relays under the hood they are both the same relay and one looks newer is it supposed to be that way? Im kind of at a loss im leaning towords the switch being bad.

[Gary Lewis]

Welcome!  Glad you joined.  

But before we get into the issues on your truck, you probably missed the email I sent you asking you to introduce yourself in the New Members Start Here folder.  And, most importantly, to read the guidelines that are posted there.  That's important as we hold everyone to them.  So, can you assure us that you've read them?

As for your truck, I'm in a crunch and can't take much time right now, but to get started you might look at the info on the page at Documentation/Fuel Systems/460 Fuel Systems, and especially the Electrical tab.  As you'll see, there is only supposed to be one relay, the Fuel Pump Cutoff relay.  So if you have two controlling the fuel system then someone has modified things.

However, there are frequently two or three relays in the same area.  Another would be the Trailer relay.  So we need to figure out what you have.  Can you post some pics?  (How to post pics is in Bullnose Forum/Forum FAQ's in the menu, which also includes how to create a signature, which will help us give better advice since we will know what you have.)

[jmadigan]

I did miss that email. But i have read the rules and have since posted in the New members area. I will get some pictures later today after work. There is alot of places the older gentlemen i bought it from has "modified" ill let you guys take a look at a few questionable areas.

[Gary Lewis]

Thanks, JM.

[ArdWrknTrk]

There were a few changes to the Hot Fuel Handling system.
Some used a pump relay only, and some used a pump and a selector relay.
This explains the 5 pin vs 6 pin socket you have.

Since pump power gets switched at the valve under the driver on the frame rail, I would look there to be sure the motorized valve is indeed switching ports and pump motor power.
You should test by reversing power and ground to the pins that shift the valve.

If the switch valve is dead you can replace it with the six port Pollak valve and pigtail kit which is ~$75 delivered on eBay.

[ArdWrknTrk]

Unfortunately we don't have the '83 or '84 EVTM available on the site.
But looking at the '85 does show that it has a four pin switch, with both a pump relay and a selector relay.

[jmadigan]

Some interesting updates. Yesterday i was fiddling around some more and discovered that the rear pump is indeed running when switched but no fuel pressure so that leads me to believe it actually is the on frame tank selector. Im going to put some pictures in here of a few things i found that were questionable to me. There are a few disconnected wires and some wires that are looped back into the wiring harness. and a shot of the questionable relays.

[jmadigan]

the orange wire wrapped around the harness was my doing there as a quick splice because of the trailer plug in the bed was wired into it which i wont be using.

[ArdWrknTrk]

Well, the good news is that if the rear pump runs the tank selector relay and all associated wiring is good.

One way to see if the valve motor is switching is to see if the senders switch and the gauge reads different on each tank.

You can also unplug it and take some jumpers from a 12V source and reversing polarity to the valve.
This should drive it one way, and then the other.

If you're under there you will definitely hear it move.

[jmadigan]

The gauge tends to read the same as the front tank when i switch it.

[ArdWrknTrk]

Which may mean the valve isn't moving to the rear.

If you look at the diagrams, the tank selector relay chooses which pump gets power, but the valve moves to change senders and ports.

So try unplugging the valve and powering it directly to see if it moves when you reverse polarity on the orange & brown/white wires.
If it does, your problem is the switch (or the wiring between switch and valve)
If it doesn't, the valve is dead.

[jmadigan]

Copy that. I will give that a shot and report back. Thank you!

[85lebaront2]

I believe the valve is available from Pollack.

[ArdWrknTrk]

Yep, that's what I said....
But you have to use their pigtail and clamps instead of the stock nylon click and lock connections.
So get the 'kit' and not just the valve.

Still, $75 is a lot better than $475 for stock (if you can even find one)

[jmadigan]

Okay guys thank you for pointing me in the right direction a new fuel selector valve did the trick both tanks are working now. Thanks again!