Dual Fuel Tank Weirdness

[HomeThtrLA]

Since I bought a used van, I have found that it is basically an E150, so I am writing this here, even though there is a mostly unpopulated forum for Club Wagons.

I bought a 1988 Club Wagon in January of 2003. It has two fuel tanks and a switch for changing from tank to tank. The switch looks like it is factory-installed.

The Haynes manual implies that there is one mechanical fuel pump on this van, and the electrical diagrams have a wire labeled "to fuel switch," but there is no diagram of how the switch is wired. I do audio/video installations, so a diagram like that would help me a lot.

The weird thing is, the second time I filled up and kept track of miles to figure out what the mpg was, I never switched to the second tank; after going LOTS of miles, I finally switched and the other tank was almost empty. It was as though both tanks were supplying fuel the whole time without moving the switch.

It never happened again. For almost two years, I have switched from tank to tank, as I figure I should.

Then about a month ago, it stalled while using the front tank. I switched to the rear, and it kicked back into full force.

Since then I have found that it will eventually stall if using the front tank, then almost immediately return to full power after I switch to the back. So I only use the back one now. But this left me with about a half tank of gas in the front. I kept trying to use the front to empty it but the gauge hardly went down.

Then one day after I filled up the rear tank to be sure I had gas to switch to, I noticed that the front gauge had increased from about 3/8 to about 5/8.

huh?

Are these tanks interconnected? Do they both pump at the same time, regardless of the switch? Is the switch NOt switching and making both pumps work?

Anybody?

[ModMech]

Actually, your van has THREE fuel pumps, all are electric. One low-pressure pump in each tank, and a single high pressure pump mounted on the left inner frame rail, below the driver's seat.

The switch on the dash controls which in tank pump is activated, and which fuel sender sends signal to the dash gauge.

The front tank may not supply fuel because the dash switch is bad, the in-tank pump (or wiring to it) are bad, or because the pick-up filter is clogged.

There is also a switch-over solenoid that directs the return fuel to the selected tank, and not the unselected tank (as the return line "T"s). If this solenoid does not seal perfectely, you could get some return leakage to the front tank. More likely, there is a bad ground connection on the front tank, which is causing both the gauge and pump problems.

[HomeThtrLA]

That's a great answer, especially the bad ground part. Bad grounds are so hard to imagine and can cause all sorts of interesting problems.

I have one problem with the explanation, but I don't have a better one. I just filled up the rear tank, and when I turned on the ignition, right away, the front tank showed more gas than it had before.

Could there be some interconnection between the level sensors that is causing this?

[ModMech]

The switch on the dash selects which sender along with the tank selection. You could be getting a cross voltage due to a bad switch.

[HomeThtrLA]

I went out to a Ford dealer, Vista Ford, in Woodland Hills, CA today to order a new switch. I asked the parts guy if they had a sketch of the schematic for the system and he referred me to the Service Department.

Man, the reputation that they push in their local radio ads is completely true! Not only did the service manager go two places looking for the book (only to find 1987 and 1989, not 1988), but he sent me out to the older mechanic whom he said was most knowledgeable about the older vehicles. The manager, this mechanic and I stood around for about ten minutes talking about how the circuit and piping worked, and what could go wrong, and all this for a guy who might or might not just buy parts from them! They push that they are a family business and they take care of their clients, and wow, they sure do!