1994 F150 fuel transfers from aft tank to front tank when aft tank is selected. what causes this.

 

There was a recall way back when for those trucks. Two check valves were installed on the fuel pumps to stop that problem. Safty recalls are good for ever check with a Ford dealer they should be able to resolve the problem.

 

There was no recall to my knowledge. The cause was a bad switching valve. Common failure item and available at most auto parts stores for a nominal fee.

-Joe