Well, my ford f150 has once again failed me, despite the money I have put into it. It has dual tanks, and the 16 gallon rear tank has been failing to work for a few months now with a full tank, but the front tank works. I have replaced the fuel filter and the fuel pump relay, but I am not sure if the problem is the pump or not. I believe the pump is in the tank, but I'm not certain. I am not an expert on these trucks obviously, but any input would be greatly appreciated. The truck is a 1989 model with a 4.9L six.


ryan

 

I'd have to say it's the pump itself, do you hear it working when you turn the key "on"?

 

if i remember right my 89 had the high pressure on the frame and the lift pumps in the tanks because my 91 has just 2 high pressure pumps in the tanks. And just by luck if the rear tank is full then ofcourse the pump is probably bad, lol. Just seems thats how it happens.

 

89 was nearly the last year of the 3 pump system. Low pressure pumps in the tanks just get the fuel down to the rail pump.

Could be pump, switch, the fuel filter sock on the in tank pump, or a few other things. ( I know most of this from other forum discussions)

I'd do everything that I could to make sure it was the pump because it's not fun to get to. Some guys here slide back the bed claiming that it's easier to do that than to drop the tank.

You could always live with it. I'm sure it's a PITA, but fixing it might not be easy.

Good Luck!

 

THE ONLY WAY I CAN GET MY REAR TANK TO WORK after switching tanks is to ground the fuelpump relay switch the switch and let the pumps rum for a few min. Then it will run on rear till i switch, when i do have to do it all over again

 

The fuel tank selector valve, located on the driver's side frame rail, is not powered by electricity--rather, it uses fuel pressure to "shunt" a mechanical valve to allow it to draw from one tank or the other.

I'm wondering if your fuel pump selector switch/wiring is bad, and not telling the rear pump to pump?

But the tank selector valves themselves do go bad--I changed mine--$65. with employee discount, from the stealership.

Perhaps someone will post with a diagnostic routine you could run, to confirm/rule this out?

Good luck.

BigSix1

 

Two circuits com into the switch. One for pumps/one for gauges. Switch toggles direction of both circuits to front tank pump & sender or rear tank pump And sender. Testing (w/key on) the 4 circuits connections out to ground should show current at two of those connections w/ switch in one position & current at the other 2 when switch is in the other position. Gauge senders function w/wo pump function. If switched to rear tank & only 1 of the 4 are showing current(and fuel gauge showing tank level) than pump contact in s/witch is bad. If current through switch showed ok for pump connection also, I'de go get a selector valve at a salvage yard for $10. & replace the one on the truck before I embarked on a tank droppin pump replacement adventure.

 

ya i'm aware that there is a pump problem...i can hear it kick on when the key is turned, and when i switch to rear tank, the pump on the frame starts whining pretty loudly. I don't have a fuel pressure gauge so I am going to have alot of fun this weekend...