Hello fellow Fordies;

89 F150 XLT, 4x with dual tanks. The PO told me the front fuel pump was out. I know there are 3 pumps on the truck, 2 lp, 1 hp. Put fuel treatment in both, filled rear tank and run on the front tank, trying to purge the old gunky fuel out. The fuel gauge is beyond "F". Thinking it was the varnish causing the indication, I tried to put fuel in front- FULL. Ok, running the front tank, the level on the gauge isn't dropping, but the rear is. Normal behavior? I wouldn't think so...My service manual dances around the whole operation. TIA!!

 

The switching of the tanks is a mechanical operation caused by pressure from the in-tank fuel pump. If the in tank pump is out like yours, then it will not send enough pressure to switchover the valves in the reservoir. It will just keep pulling the the back tank. The fuel pump on the frame rail is strong enough to pull fuel even if the in tank pump is not running.

Long story short, most likely your front in tank pump is out, and you will not get it to pull fuel until it is replaced.

 

Paint;

THANK YOU! That makes sense!!!! No mechanical valve, it relies solely on the pressure....the switch on the dash is for pumps and gauge only?

High 5!!!!

 

You are spot on. The switch only changes the power to the in-tank pumps and which tank it gets a fuel level reading from. Glad I could help.

I reccomend pulling the bed off to change the pump. Makes it way easier, and you can do fun stuff like clean and paint the frame

 

Awesome Paint...many thanks!!!

 

Fuel Tank Selector Switch applies power to the Front or Back pump and the sender.

(The fuel gauge is beyond "F".)

If the wire from the Fuel Gauge via the Fuel Tank Selector Switch to the Fuel Gauge Sender is not connected, the fuel gauge will read beyond "F" – Repair wire.

If the wire from the Fuel Gauge Sender to ground is not connected, the fuel gauge will read beyond "F". - Repair wire.

Check your wiring and connectors.

If the Coil/Wiper in the Fuel Gauge Sender is faulty/open the fuel gauge will read beyond "F". – Replace sending unit/Pump assembly.

Your Fuel Tank Selector Switch could be faulty.


(The PO told me the front fuel pump was out)

Check wiring (power and Grounds) to front pump. Verify pump is running or not.

If the front pump is out, the Dual Function Reservoir will not switch to the front tank.

Your Dual Function Reservoir could be faulty.

Thanks Subford for the drawing.

 

Thanks Vjsimone/Paintslinga2010/Subford, thought it might be the switch, no luck. Both pump and sending unit bad. Grounded the sending unit wire and the gauge moved down...

So I'm at RockAuto, looking at a Delphi HP10149 which according to RA is a replacement for Ford's E7TZ9H307BA. Anyone have any disputes with Delphi? Not buying cheap and plan on this lasting a while...

 

Yeah, shorting the Gauge to ground will cause the needle to peg to "E".
Not sure how that proves a bad pump and sender.

Did you check the Grounds? Is there power to the pump?

 

With my 88 F150 both tanks read past "F" when full and stay there until about half was used then the needle would come down and be accurate when close to "E". I reset the trip meter and use that to help gauge how much fuel I have. I recently seemed to have experienced a DFR (Dual Function Reservoir) failure as the rear tank started filling the front tank. I stopped using the front tank years ago because it had a small leak. Subford has info on the DFR.