There are times when the pump will shut off just seconds after starting to pump and times when it will overfill and spill gas. It has something to do with the fuel vent hose and it is very common. I have this problem at some stations, but not all. This may sound crazy, but when I start to pump the gas if I can hear a gurgling sound, I know that this will happen. If the gas flows quietly, I can lock it on and it will shut off when full without any problems. It has to have something to do with the way that the vapor recovery collar on the pump is made. The small collars that fit easily into the area around the filler work fine, the larger ones give me problems every time.