Hello,
I'm having trouble figuring out how the fuel selector works on my 1990 ford w/a 351 EFI engine. It will not switch over to the forward fuel tank (and that tank reads empty) but it will not normally die on me (I believe it is still pumping from the rear tank?). It works well off the rear. I know I have a switch inside that has 6 conductors (I have check all conductors functionality with a ohm meter w/switch in both positions). The switch works, but I believe I have a faulty selector valve? I cannot figure out how it works, though. I can find no electrical leads going to the valve itself. I only see 4 fuel lines going into it (2 from each tank) and 2 fuel lines leaving toward the front of the vehicle (one goes to a pump then to a filter, don't know where the other one goes or what its purpose is). The 2nd line doesn't make sense to me. Was I looking at the selection valve? Or is the fuel selection made by disable and enabling the booster pump (I think I have these) inside the tank and this is serving as a merging point (with no selection made at this point)? If so, I know that I may have a bad fuel pump. I know I am long winded, but I want anyone who knows to understand my problem. I appreciate any help!

I don't know if you have solved your delima but I've been working on the same situation. I have learned that the switching is done with the pumps in the tanks. The diverter valve underneath the cab is not electrically switched. According to Ford, that used to be a filter which they say no longer does that as they have changed up the part but it does act as a diverter. My understanding is that changing the switch to another tank changes the fuel flow. If you can't get fuel out of another tank then check the pump in the tank as it may not be working. You can test this also by removing the fuel line from the diverter valve and powering the pump and see if fuel comes out of the line from the tank. Hope this helps.

Very good advice! I'll try undoing the line from the front tank and see what happens. The pump is very difficult to reach and the tank is full of gas so removal will be hard. Every tube I try to stick down in the tank will not go past the bend in the fuel filler pipe. Thanks for the helpful advice!

I've had many problems with those diverter valves. The most common problem I've seen is being able to pump out of both tanks, but one tank overflows. This is because even though you've selected another tank, the unused fuel returning from the engine keeps going into the same tank beacause the diverter valve isn't switching also. I haven't nailed down it's operation completely, but I do know it uses the fuel pressure from one tank to close off the return of the other tank using a diaphragm. Don't worry about tryin to fix it, it ain't gonna happen. The part isn't even available at the dealership.. I've fixed a few by disabling a tank, and using fuel filters in place of the valve. The filters have the same quick connect fitting as the valve.. As goose said, you need to check the in-tank low pressure pumps, as well as the high pressure pump mounted on the frame rail, in between the valve and the engine. These can be tested by having someone turn the igntion on, engine off and listening to the tanks. Just switch the tanks and turn the igntion back on to test the other one. If you start taking off fuel lines though, be prepared for a MESS! Most of the time one tank is full, and when you pull off the line, gravity will drain quite a bit out. As for the lines, the big ones are the pressure lines, the small one's are the returns from the engine..

I just recently talked to a technician at a dealership and he pointed out that Ford had come out with a service bulletin regarding the overfilling of one of the tanks because of the other tank. The solution they were conducting was installing check valves on the tanks. He said it was easy but that's anyone's guess in my opinion.

I'm going to try disableing one of the tanks and see if I get any better milage, but I'd like to have the two tanks to get better range. Thanks for the help!!

Hi,
I conquered my fears and decided to take out the forward tank and found that the pump is indeed bad. I fiddled with the float and got it to give me a gas reading, but the pump itself doesn't work. Tested the voltage and there is 12 volts going to the pump (connection is good all the way to the terminals inside the tank), but the pump must be either fried or there is too much corrosion for the electricity to flow through it. Will replace and hopefully have a reserve tank!

One question, though. The lines that go to the pump are not coming off. I removed the metal retainers, but it seems there is some tabs inside that I can't get to let go of the pump lines. How do I remove these? Thanks!!

Oh, when I disconnected the forward tank, nothing came out of any gas lines. I assume that means that the gas will not flow b/w the tanks, right? Not that it matters if I fix the pump in the front tank.

The removal of the couplings on the lines requires a special tool to spread the spring clip inside that locks it in place. Its very similar to the little plastic tools used for the spring lok couplings on ac lines. In fact they will work if youre careful. Or u can fabricate some by cutting strips from a 5 gallon bucket, heating them and forming a small circle, and cutting them the right length for your line. The plastic on the bucket is the right thickness, and works good. When you slide the tool in the coupling, gently try to pull the line apart, dont force it or youll bend the ears on the clip, then u got a problem, not only getting it apart, but finding the clips. When u get the clip spread properly, itll come apart easy. And u are correct, gas will not siphon through the pumps, and the lines have check valves in them. Good luck.
Later
Ed

Thanks for help. Ended up not removing the lines. I just replaced the pump itself along with the filter basket in the tank. This didn't require I remove this line. Thanks for your help again!
Regards,
Micah