Pressure vaccum, if the car is running right don't worry about the pressure. Means your fuel system is tight, imo.
I get pressure sometimes depending on the temperture and both my cars are vented just like the factory vented them.

A vented fuel cap will leak down the side of a challenger. I'm sure lot's of guys here have done it and it's not pretty.

71 factory service manual.

74 FSM.

Last edited by Challenger 1; 05/10/12 06:15 PM.