89 F150 4x4 Dual Fuel Tank Switch
 

I've developed an interesting fuel supply problem in my '89 F150 4x4: The front/rear fuel tank selector switch appears to be malfunctioning. Although the fuel gauges appear to accurately reflect the status of each tank, flipping the selector switch does not appear to effect which fuel pump is active.

My F150 only pumps fuel out of the front tank regardless of whether the switch is in the front or rear position. Interestingly, the fuel level sending units in each tank appropriately display the correct fuel levels for each tank.

Its a bit frustrating, as when the switch is in the front position, it pumps out of the front tank and accurately displays the fuel level in the front tank. With the switch in the rear position, it pumps fuel out of the *front* tank and accurately displays the fuel level in the rear tank, which never changes.

This ultimately leads to one of two situations, both of which had to happen before I had realized what was going on:

1) With the switch set to the REAR tank (which is full), the gauge shows the full level of the rear tank while running the front tank dry. The net result is that you run out of gas in the front tank as the fuel gauge displays a full rear tank.

2) With the switch set to the FRONT tank, the gauge accurately shows the reduction in fuel level as fuel is consumed from the front tank. Unfortunately, when the front tank runs dry, switching to the rear tank shows a full tank of fuel, but the fuel pump in the front tank continues to pump out of a dry tank -- the rear pump will not activate. You're out of gas while you have a full rear tank that you cannot access.

Am I correct in assuming that the fuel tank selector switch on the dash panel performs two functions (as in a DPDT switch), with one side of the switch selecting which tank's fuel level sending unit is connected to the fuel gauge, and the other side of the switch selecting which fuel pump is active? If that's the case, it seems as if a relay or a solenoid valve that controls the fuel pumps is malfuncitoning somewhere. Maybe its just the dashboard switch.

I understand that the F150 uses a low pressure fuel pump in each tank, and that pairs of supply/return lines from each tank go to a reservoir unit. From the reservoir unit, a single pair of supply/return lines go to the high pressure fuel pump, which goes to the fuel filter and up to the engine compartment.

This has led me to the following questions:

1) Can anyone offer any ideas as to where I should look for the problem? Is it more likely the dashboard switch, the dual function reservoir, or a check valve in one of the fuel pumps?

2) My Chilton's manual refers to a "Dual Function Reservoir, 9B263." Is this the same part that others have referred to as the "selector valve" that was covered by a recall on 1989 models?

3) Can anyone recommend a better manual than the Chilton manual on 1987-1991 full-size Ford trucks? (Part No. 8136). The Chilton manual has left quite a bit to be desired every time that I have used it.

Thanks!

Bob

89 F150 4x4 Dual Fuel Tank Switch
 

it sounds like your fuel tank selector valve is bad.it's located on the frame rail between the tanks and the filter

89 F150 4x4 Dual Fuel Tank Switch
 

[font size="1" color="#FF0000"]LAST EDITED ON 08-Oct-01 AT 11:03 PM (EST)[/font][p]I have a similar problem but I have assumed that the low pressure pump was the problem. So this post has made me think again about what I had assumed. I follow that the valve would likely be the problem with the predaina's 89 because the fuel continues to be pulled from the front tank.

I have an 87 that doesn't run for long on the rear tank. It runs for awhile off the resevoir. My question is how did you determine that the pump inside the tank is actually running?

89 F150 4x4 Dual Fuel Tank Switch
 

Change the dash switch. about $25.00 through ford. I had a similar problem with my '90 f-150. Your right about the switch being a dpdt switch.. 1 side for the fuel pumps and the other side takes the gauge. Hope this simple fix works..Gary

89 F150 4x4 Dual Fuel Tank Switch
 

I crawled under the truck and listened to the fuel pumps as an assistant put the ignition in the running position (in between accessory and start). This activates the fuel pumps to bring the injector manifold up to pressure without cranking the starter. With the truck running, it was very noisy, and difficult to hear whether the front pump was working. I've found that it was alot easier to hear which pump was working by having the ignition turned on but the truck motor not running.

At this point, I positioned myself between the front and rear tanks and had an assistant switch back and forth between the front and rear tanks to confirm that the sound of the low pressure fuel pump moved from tank to tank. Its best to get between the two tanks to hear the sound move from front to back, as the high pressure pump is a bit noisy and can confuse the issue. I felt more confident in my assessment of which pumps were functioning when I got under the truck and put a hand on each tank while the assistant switched back and forth between tanks. I could feel the vibration of the fuel pump in the appropriate tank when the dash panel selector switch was thrown.

Thanks, Gary. I pulled the switch and tested it out of the truck. It looked brand new (no charred terminals) and tested fine. I was really hoping that the $25 solution would be the right one.

At this point, it appears that the problem isn't in the switch. It seems that its either in the dual function reservoir or in one of the pumps.

So this leaves me with a few questions:

1. Can anyone explain what are the two functions of "dual function reservoir"?

2. Is the dual function reservoir the part that everyone here is calling the diverter valve?

3. Does all of the fuel diversion take place in the dual function reservoir? That is to say, does *any* fuel diversion take place in a check valve in the low pressure pumps located in the tank, or does the 100% of the diversion take place in the dual function reservoir? It would help for me to know if the low pressure pumps are a single function device (pump fuel only) or a dual function device (pump fuel and divert fuel when shut off). If they're a dual function device, this would suggest that fuel transference from front to rear could be a fault in the *rear* pump.

Thanks!

Bob

89 F150 4x4 Dual Fuel Tank Switch
 

Any solid answers yet?
 

Hello...new to forum...and I'm having the exact same problem with my 89 F150, it's not 4x4 though. Anyone been able to confirm a repair for this one? I'm in Guam and parts are expensive and the Ford dealership here wants to replace the entire system to fix it :-X15

Just a quick note...right before my tanks stopped switching...when I would switch to the rear tank it would sputter a bit...only did this about 3 or 4 times then just stopped pulling from the rear tank at all

From your description, the rear in tank pump is bad. The dual function reservoir is mechanical. The pressure from the in tank pump switches the mechanical valves.

The dual function reservoir serves two purposes.
1) Mechanical Selector valve for the tanks.
2) Holds extra fuel in the reservoir so if the gas tank is low on fuel and you go around a turn and the low pressure pump can't pump any fuel, the high pressure pump can still draw fuel from the reservoir.

http://i135.photobucket.com/albums/q...elsender-1.jpg

Yes the rear boost pump is bad and the one and only check valve is in the High Pressure pump on the frame.
https://i54.photobucket.com/albums/g...Fuelsystem.gif

I'd completely agree about the rear in tank fuel pump being bad. I had an 88 which had a similar issue about not pumping from the rear tank. One day on my way to work, I was running low on gas in the front tank, so I switched to the back tank. Unfortunately, the pump wasn't working (I didn't know it at the time) and it starved the high pressure pump of fuel.
Well, I learned my lesson that day - the truck stalled on the highway. I flipped the switch back to the front tank and attempted to start her back up. No luck, she was dead in the water. I ended up blowing the high pressure pump when I flipped to the rear tank and it was starved.

I also read post back then, that basically said what was happening and why.
The reason that the truck continues to run is because the high pressure pump is pulling gas from the front tank without help from the low pressure pump. When you flip the switch to a tank with a broken pump, you're basically shutting the low pressure pumps off altogether. Trust me, your frame mounted pump (high pressure) is definitely working a lot harder if you're running like this.
And I agree with F150xlt, the switching action must be mechanical based on which pump is supplying fuel. (For some reason I remember an electrical connector on the selector valve, but I think it's just been awhile since looked at one).

My advice - make sure that you don't change the switch on the road if you know that your pump's not working. You could end up needing a tow.
Good luck!

Does a 1990 ford f150 4x4 with dual tanks have low and high pump? I dont see it anywhere all i hear is what sounds like 2 high flow intank pumps?

No you do not have low and high pumps.
A 1990 f-150 just has one hi-pressure pump in each tank.
Here is a diagram of your 1990 system.

http://i54.photobucket.com/albums/g9...FielSystem.jpg

/

Bill,

Can you put up a diagram for a 93 F150 2WD short bed with the 4.9l I6?

Thanks,
Rich

Can you be more specific, the fuel diagram for a 93 with two tanks is the same as the one in post #13 right above your post.