Fuel Line for Auxuliary Tank in 86 F250

I have the big block 7.5 liter engine, and I’m tired of having to fill up everyday. (I have an hour commute each way). On this car, the tanks both run off the same pump, so if it gets gas, it has to be working for both.

Where should I look for problems? There is no obvious break in the hose coming from the aux. tank.


You never actually say what your problem is. Is it that if you flip the switch over to the Aux tank then the truck will sputter out and stop running?

Did you check the selector valve? Those seem to go bad fairly regularly, especially if they don’t get used very much.

I have an '86 E350 and use the same pump for both tanks. I put a BIG filter just before the pump and tank selector switch. You ARE NOT going to get better mpg ratings if you don’t :

  1. keep that big pig in tip top mechanical condition,
  2. a clogged air cleaner can rob you of a quarter tank of gas EACH fill up.
  3. change spark plug wires every 2 years or so…BTDT…
  4. big ford engines ( mine’s a 460) don’t like copper tip spark plugs.
    hope this helps

Ah… sorry. When I switch the selector, the truck sputters and stops- The solenoid is doing something- I can feel it shift with my thumb when the switch is thrown, but it doesn’t draw gas from the aux tank.

Let the phun begin !!!

  1. take off the gas cap to the aux. tank.
  2. carefully undo the gas line leading to it and blow the gas line out with air.
  3. have someone do the selector switch back and forth.
  4. re-hook up the gas line ( after putting a see thru filter) in line and try to run off the aux tank.
  5. replace the switch if that doesn’t work.
  6. you may have to put gas filters between both tanks and the pump.

with a vehicle this age , you will be amazed on just how much the filter collects.
also try octaine booster each tank. I get mine at the Dollar tree for a $1.- a bottle. gets an evtra mile or so per gal.

Good suggestions. I would suggest that the valve is not actually moving all the way to the aux tank, but getting stuck half way. You can buy replacement valves for not very much $, Ford seems to have used the same one for a lot of years.

Theres a low pressure pump in each tank that feeds the high pressure pump on the frame rail.

Looks like the tank pump isnt running.

Give the tank a good whack with your hand & see if that gets the pump going temporarily.