ok i have a 87 ford f150 xlt lariat 4x4 and a 302 . it runs duel 19 gal tanks . i just replaced the rear tank sending unit and pump . also have replaced the high pressure pump on the rail and the fuel valve for the six lines . and i am still having the same problem . my front tank is over flowing out the neck and building pressure . also when i put gas in the rear tank it for some reason is being put in the front tank . i can have a haft tank in rear put the switch to front tank witch gas hand reads for it a day latter flip back to rear tank and my gas hand has moved down . the front tank stop working a long time ago but now since i replaced the rear tank i can have the switch on for that tank and it works. hope someone can help me with this

 

Go through this thread.

fuel-and-fuel-tank-problems-please-help

 

First I would check the lines from each individual tank at the valve. The supply and return lines from one tank at the valve itself should either be horizontal or vertical to one another, not diagonal, If so you would be feeding the valve from one tank and returning to another. Secondly if there are any restrictions in the lines or low pressure pumps in the tank the valve may not operate properly. The restriction holds pressure in the lines on the tank that is not selected and will not allow the valve to completely shift from one tank to the other. ie if the supply line in the tank thats shut down does not bleed off pressure it holds the valve partially open allowing the fuel to return thru the return line to the wrong tank. You should be able to blow air back thru the supply and return lines into the tank on the low pressure side of the fuel system. Third I know you said it was a new selector valve however it wouldn,t hurt to test it. Remove the supply and return lines from one tank on the valve. put two short hoses on the open ports on the valve into a container [for safety reasons]. Select the fuel tank that the lines are still connected and cycle the key several times, initially their may be a small amount of fuel out of the open ports of the valve until it completely seals. There should not be any leakage out of the open ports. Reinstall the lines, remove the lines from the other tank and ck. their open ports. If there is no leakage out of the open ports the valve is functioning properly.

 

Both front and rear in-tank pumps must be working in order for the valve to function properly.
See link in my signature.

 

wow thanks guys for that info . cant say how much that link helped klricks . i was going to just remove the tank on my day off but now i thank i am going to change the pump in the front tank and hope for the best

 

ok went and bought new tank pump and sending unit today i hope it will make all this right . i will give an update when i get it all done . also had to buy a new exhaust manifold . i sorta cracked one with a breaker bar slip .