While fueling up my freestar the gas spits back out. The ventilation system must be plugged but it looks very complicated. Where do they plug?

Two issues:

Slow filling - the hose that connects to your fuel tank from the fuel fill point is a rubber hose. Sometimes, either at the time of manufacture or when some type of tank work has been completed, the hose is not installed properly and is installed with a "kink" in it. You should be able to go under the vehicle in the area of the fuel fill point and see the hose I am speaking of. If it is pinched, the hose needs to be loosened and repositioned to take the pinch out. Sometimes the hose needs to be shortened.

Hissing - The fuel tank is not vented to the atmosphere. There is actually a vacuum hose that runs from the carbon vacuum canister located in the engine compartment to the fill point that draws fugitive vapor from the tank. This means the tank should always be under slight vacuum and you could expect to hear it pull a little air in when you remove the cap.

Sound like the rolover valve is stuck shut. I work for Chrysler and they recalled all the 05 06 durango fuel tanks for this condition. The valve is built into the gas tank. Check with your dealer to make sure there r no recalls for this concern. This can be a big fire hazard if I were you I would call Ford I will garuntee they will submit this claim under warenty. Good luck hope this info helps.

This is most likely the anti-syphon device in the filler neck. It can get debris build up or the pump nozzle is in too far. There is a small chance the ventilation hose to evap canister may be plugged.
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