My gas tank cap used to release a small amount of air/pressure that would build up in the fuel tank. The gas cap had a button that you could press to release the pressure before unscrewing it. A few months back I noticed that the pressure was non-existant so I bought a new gas cap thinking it would fix the issue. With the new gas cap installed I still do not have the pressure build up

1. What are the side effects of not having a pressurized fuel tank?
2. Would the vapor canistor have anything to do with the lack of pressure?( I noticed the vaccum/rubber hoses on the vapor canistor are getting hard and I will be replacing them soon.

 

It's always better not to have any pressure build-up in the fuel tank, as it is the result of the acumulation of fuel vapors, wich are highly flamable.

 

Excess pressure in the tank is a result of expansion typically due to heat or a greater amount of air than fuel in the tank. Air expands more readily than the fuel. The truck doesn't produce any real pressure into the tank at any time. In fact, the more evenly matched the pressure in the tank and the air outside, the better the system will perform. The most likely reason for the change is the aging of the components and portions of the system that seal the fuel system.