When attempting to fill my gas tank, the gas pump fills for only seconds and cuts off as if the tank is full . It repeatedly does this making filling the tank take anenormous amount of time , even when the nozzle is squeezed to a minimal degree. Gas backs up in the fill tube shutting the nozzle off. This doesn't happen all the time but does happen. Just recently I went tried 3 pumps at one gas station and one at another station experiencing the same problem.