konlin

ok, I am brand new here and have searched for the last few hours and haven't seen this exact problem listed so I figured I had better ask the experts. sorry about the long post, just trying to answer the questions right off the bat.

I have a 1987 F150 4x4 that I just purchased (recently painted so no decals or emblems on the sides so cant tell you exact model) it is a standard cab, 6 1/2' bed, dual tanks
#1 - no matter what position I put the tank selector switch in, the truck is running off of the front tank.
#2 - no matter what position the tank selector switch is in, the fuel gauge reads empty ... not below empty, just empty

If i turn the switch to on and have my son under the truck listening he says he only hears the front tank fuel pump no matter what position the switch is in.

I have taken the tank selector switch off and tested it with a multimeter and it seems to test fine

I have not been able to find a good wiring diagram for a '87 f150 fuel system but I found one for a '86, I checked voltages and I got 10.7v (not 12+ ??) to ground through the switch at all the right places and I get about 1.7-1.8v back from tank going to gauge.

I do NOT have fuel pumping from one tank to the other (thank goodness)

If I disconnect the fuel tank selector switch completely and then turn the key my fuel gauge reads above full (this indicates gauge itself is good .. right?)

I realy hope someone has an answer for this one, it is driving me nuts.

I am going to the parts store this evening on the way to work and am hoping someone will have some ideas so I know what to start buying.

Good old Bill

Am asking what type of valve you have? In that era or before Ford used a valve with 6 lines to it. Upon failure only one tank would feed. Two lines from each tank with feed and return from engine.

konlin

yes, I have the fuel transfer valve mounted on the frame below the drivers seat that has 6(?) lines to it.
So, if this valve fails, that can cause the lack of switching tanks.?.
If that is the case, when I am switched to the other (rear) tank, will the engine still run?
I ran the vehicle 1 day on rear tank switch position and then fueled up at the end of the day and my rear tank was still full but the side tank took my normal amount of fuel for one days travel.
Would this problem also explain the lack of fuel gauge working for either tank?

Just call me Sean

iTrader: (1)

'89 and before doesn't have the crossfilling problem because of the different switching system. I don't believe the dual function reservoir (what was called the valve) has any electrical plugs to it, so there shouldn't be any electrical switching problem with it. Not exactly sure how it works, probably some kind of flapper that is pushed to one side when a tank pump is pumping. Sounds more like a switch problem, or someone has messed with the wiring to the pumps because of a bad pump. If you just bought the truck they might have wired the switch to run one pump so you thought both were working. At the switch the power wires to the pumps are red for one and brown with a white stripe for the other, not sure which is which. Depending on where the wires were messed with you can try testing there but if wires were spliced elsewhere then that won't help. Remember you have 3 fuel pumps, one on the frame that is on for either tank and one in each tank. Fuel gauge is a common problem with these trucks and is most likely the fuel level sending unit. Good news is the sending unit is cheaper for our year trucks.

Good old Bill

Check the valve out for an electrical connection as Sean said, my memory has been off before. If it has the connector check for voltage as your son is switching the selector.

konlin

I will check that today when I get home if I can, if not I have tomorrow off. (I have been working nights this week)

I will check the selector valve for wires and see if there is voltage there ...
I will also see if I can find any spliced wires, I didn't see any directly behind the dash mounted selector switch.

If that looks ok, then I guess my next step is to try to check voltage on the tank fuel pump(s) wiring while my son turns the key ... definitely time for blocks and E-brake hehe.

I stopped at Napa auto parts on my way to work today and they had no clue what parts I was talking about.
Is there another name for the fuel tank selector switch and the fuel tank selector valve? or does anyone know the part numbers?

Sounds like I may be looking at level sending units for both tanks also, yikes, this could get expensive.

Let me know if you have any other ideas that I should check, thanks for all the help so far.

Just call me Sean

iTrader: (1)

As I said earlier, the fuel tank selector valve is called the dual function reservoir. For single tank trucks it's called the single function reservoir. I doubt there's a problem with it. I don't know what else the switch would be called but it is easily tested, plus you said you already tested it. If it has power out of one wire and when you switch it then it has power out of a different wire then it is okay. Check for power out of the switch at the color wires I posted above.