I own a 1986 F150 Super Cab XLT with the FI 302 AND C5 Tranny. The truck also has dual tanks.
The problem I have is with the rear (main) tank.
I cant get any fuel from it.
Currently the tank is full but when I place the tank selector switch from front to rear, the fuel gage shows empty but yet the fuel will continue to flow from the front tank. I tested the tanks out by letting the truck run on what I thought was the rear tank until it went dry and when I got it to the gas station instead of the rear tank being empty it was the front. The rear was full.
I checked the wiriing and that was straight and the haynes and chiltons manuals dont mention much about dual tanks.
A sticker in the engine compartment says there is an automatic fuel pump shut off switch that can be reset but I have yet to find it and I dont have an owners manual for the truck.
Any help in this matter would greatly be appriciated. Its getting expensive refilling the front tank every few days.

 

I've a similar problem but my rear tank drains for only a short time then the engine dies until I switch to the front tank. When the engine dies the rear tank fuel guage reads empty. Is there a selonoid the directs which tank will be used? and could it be that it is sticking and in my case closes off the rear but doesn't open the front while in your case it never opens the rear?

 

Ill have to look again in the Haynes manual ,since it is not mentioned in the Chiltons, I briefly looked at it bu the problem in both of our cases seems to be some wiring in the switching unit along the left side of the frame and a problem with a black cannister looking part, I forgot the name just behind it. The fuel pump seems operational as does the sending unit.
Supposedly though even if the fuel has been cut off the fuel gauge is supposed to read the current level in the tank.
I will read a little more then repost, but it seems more of a need to replace old parts I think.

 

Red, it sounds like the problem with your truck is the switching valve itself.
Timmy, can we have a few more details on this? does the front tank overflow when you run off the rear tank?

 

The latest version of the Haynes manual (apparently there was an earlier version that did not have much info on this system) covers the dual tank system in great detail. It has a full diagnostic procedure for both an early and late version of the dual tank arrangement.

Essentially, there are two tanks, two pumps, two fuel level sending units, the dash switch and a selector valve on the frame rail. The selector valve functions from the dash switch and allows gas to flow from either the front or rear tank. This also includes the selection of returning the excess fuel back to the tank that is supplying the fuel. Of course, for the fuel to go through the selector valve the fuel pump has to be working.

I hope that helps,

Mark

 

The front tank does not overflow. Not having seen how the valve works, I can only immagine that if the valve has a center position to which it goes when I get some fuel out of the rear tank and then moves to the front tank when it gets that signal. With two fuel pumps and two sending units, the rear tank signal could go to the guage and read empty when the valve moves from the rear to the center and then correctly again when I select the front tank.

 

NHTSA ID No.: 91V-146
Date of Company Notification: 9-4-91
Make: Ford
Model: Econoline
Model Year: 1989-91
Model: F-150, F-250, F-350
Model Year: 1989
Number of Vehicles: 350,000
Mfg. Campaign No. 91S39. Fuel tank, auxiliary. DOM: 2/89-2/91. Dual function fuel reservoir may malfunction and cause an overfill condition in one of the fuel tanks, resulting in an overflow of fuel past filler cap. Overflow of fuel past filler cap causes a fuel leakage, which can result in fire when exposed to a source of ignition. Correct by replacing dual function fuel reservoirs with new reservoirs containing o-rings of a revised material.

 

Had similar problems E -150 two tanks 3 pump, in the tank pumps are low pressure the third pomp is a high pressure locator on the rail just in front of a black cannister looking selector switch ,which is not Electrical, it works off the pumps in the tanks the pressure from the pumps is what switches the valve, then the high pressured pump picks it up from the black canister that is located on the rail, if the pressure from either one of the tank pumps is not high enough to to switched the valve in the black container your high-pressure pump starts to make a whining noise your fuel injector pressure drops but not enough to stop the engine from running and fuel pump from one tank to the other because the valve isn't completely closed I replaced the black box didn't help so now I'm going to replace the rear fuel pump in that tank...

 

If mine has the three pump system (earlier comment indicated '88 had three and '90 had only two and it was unknown what '89 had) I should be able to trouble shoot with out throwing parts at it. Thank you.

 

Good info, ill have to trouble shoot with mine as well. Most likely a trial and error thing unless you really know what you are doing

 

While at the autoparts store for something else, I asked about the dual tank valve and he had one and showed it to me. Along with having to inlets and outlets, what looks like it could house two small solonoids were apparent. The wide electrical connector also looks like it could be suspect. That is where I am going to start.