I need some HELPPPPPPPPPPPPP! I just bought an 85 f350 4 door dually. it has a 460, 4 barrell, c-6 automatic, it has dual tanks,& electric fual pumps in the tanks, it's a non catalyst vehicle. Today i was driving it home with my 24foot car trailer in tow, it was about 70 degrees outside. After a while i had to get gas, when i pulled into the gas station i released the gas cap & it released a whole bunch of air, so much in fact that you could here the tank pop! i then went on down the road after putting about 4 gallons of gas in it, from that point on every time i got to a hill it started running rough, finally it got so bad that it started cutting off. when it cut off the first time i went back to the tank i was using & released the gas cap again, when i did it once again released a hole bunch of air, this time also spewing gas on me. i also had to get it jump started because it was hard turning over, this time though i released the fuel filler cap for good just like you would a radiator cap when the cooling system is leaking. it continued to start running rough & then cutting off every time i got to a hill, then having to be jump started every time i came to a hill. the tank i was using was the back tank.is it vapor locking or what? what can i do to fix this?if you need any more info from me let me know & i'll give you whatever you need!

 

There is a Vaccum Canister that is in the engine compartment that has a air line for the gas tank, either the canister is full of fuel or you have a hose line that runs to the tank pinched......The canister is usually black, round and shaped like a coffee can. It has the lines that run from there to the gas tank. It is used to let air into the tank to keep it from creating a vapor lock condition.

 

What I found today is that there is no vacuum canister on my truck. Due to it being a non catalyst truck it had little vent plugs on the end of a short hose hooked to the end of the vent valve on top of the gas tank. I called the local Ford dealer where I used to be the body shop manager & talked to the parts manager he told me that the f350 with the 460 in them & the ambulances of the same year had this problem, the solution was to replace the vapor separator valve, come to find out they were defective & would cause this problem. I told him to order me one & I would try it!