I have an 89 F250 with the 460 and dual tanks. I have been having a problem with the evap canisters filling with gas. The fuel pump in my front tank has been on the fritz so I have only been using the rear tank. When it is hot out the problem is worse. If the tank is full and I open the filler neck gas will pour out. I have emptied the evap canisters and replaced the purge solenoid.

I have read about some other issues where people have a problem with the fuel pumping from one tank to the other but haven't found much on this problem. Does anyone have experience with this and advise on how to fix the problem?

 

You have the fuel transfer problem where fuel is pumped from one tank to the other while you drive. This will continue until the tank is full and the evap system is flooded and then gas will back up the tank filler tube and pour out on the ground. The fix is to replace the FDM in the offending tank or disconnect and plug both lines going to it.

 

I'm guessing FDM is fuel delivery module. I assume the charcoal in the canister is shot at this point too.

 

Yes FDM is fuel delivery module but I don't know about the charcoal.. can that stuff be damaged by raw fuel? And if it was would it really matter?

 

89 trucks have the canister on the frame rail with the valves in it. If the in-tank pump is still working but weak it won't close the valves and create this problem.

 

We're talking about a different canister here for tank vapors only, your '89 has one too it's on the frame just below the rad... or at least it would have been there originally.

 

Yes I understand the vapor canister stuff. But we are trying to figure out how the fuel got in it in the first place, right?