Car is 1997 E320. I usually buy my gasoline at the same station which has many sets of pumps. The past two or three fills have presented a problem. The pumps shut off after only a small amount of gas has been pumped. Removal of the nozzle shows that there is a pressure build-up in the tank. I can then start the pump again and the same thing happens. Eventually, I can get the tank mostly filled. Isn't there supposed to be some way for the air in the empty tank to escape as you fill it? I assume it would be some part of a closed system so that gasoline vapors are captured? Could I have a valve/solenoid that is not opening when I turn off the ignition? How does the closed system function differently with engine running and not running? Car is running fine as far as I can tell. Thanks.