'02 Mountaineer gas fill issue

Hey guys, thanks for your site!

I have an '02 Merc Mountaineer w/ a gas fill issue. The car has ~75k miles, and it's a V8, 4.6L. For the past year or so, when I go to fill the car with gas, the gas will fill up the filler neck right away and kick off the pump handle. I've checked the filler hose for obstruction all the way to the tank and there is none. I"ve depressed the check valve @ the inlet of the tank, and it depresses well into the tank. I've even disconnected the vent hose from the evap solenoid & canister after checking the vent hose for obstruction. It will still almost immediately shut off.

This problem just "happened" to coincide with an incident where I was putting a bottle of Lucas gas treatment into the tank.I noticed that the small styrofoam cap seal on the lucas 4 oz bottle got washed down the filler neck. I'm really not for sure that this is the problem since it's a relatively small piece, and again, the check valve @ the inlet of the tank moves freely.

I've also felt around (as well as I could w/ tank still installed) at the inlet of the gas tank to see if I could feel the cap seal, but I just feel ridges at the inlet as well as the check valve assembly.

Again, I've checked the filler hose and vent hoses for obstruction, and they are free.

Any ideas?

Thanks,

Rod