1991 f150 rear tank leaks-losing fuel from front tank.


Asked by Jan 31, 2016 at 10:18 PM about the 1991 Ford F-150 XLT Lariat 4WD LB

Question type: Maintenance & Repair

Bought a 1991 f150 three days ago, only has 70k miles on it. Dreamed about this truck for a long time. Yesterday I topped off both tanks (when I got it front was empty and rear was at half). This morning, I found that the rear tank was leaking a lot of fuel. When I checked the tank selector switch to see how much I lost, the gauge read as the rear tank was full, even though that's where fuel is leaking, and the front tank is almost empty. I have not driven on the front tank at all.

Google search turns up a lot of people who lose gas from rear to front, mine appears to be front to rear. Is this a bad tank selector valve?

I am totally lost on this one. Is it possible for the front tank to fill the rear tank causing it to overfill and spill out? Seems to me like that would mean I have a hole in rear tank, but why am I losing gas from fronttank?I am not good with mechanics, so if you have to dumb it down for me-no problem.

4 Answers


Yes Fords do have a problem with the tank switching valve and it does just what you are describing, it is no longer serviced by Ford but aftermarket might still have it, I know CarQuest had them before they left my area. It looks like advance auto took over all the old CarQuest stores out here. I hope you can still find one. HTH


Maybe FordNut would be all over this- but he is gone- and I am not in a good mood today- so here's my reply to your problem, since you don't want to take it to a mechanic: "This is the truck of your dreams?! Thank god I dream about Italian cars" signed, Jam'n


Yes incase you unaware of how fuel injection works, there are too few lines 1 of the fuel lines is a return line. The gas pump pumps it to the motor. a pressure regulator sits at the start of the return line aligning every thing above the required pressure the flow back to the tank. When the valve goes bad the fuel line return goes to the wrong tank overfilling the one and emptying the other creating a fuel leak. You would probably be OK just running off the back tank since that is where it seams to be stuck on the return


Replacing switching valve would be a place to start

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