Car is a 94 Accord EX. I noticed that after driving the car and letting it sit for a few hours that there is still pressure in the gas tank. I can hear it escape when I open the gas cap. I am thinking that there should be some sort of relief valve in the system, or maybe the gas cap itself. Does such a thing exist, and should it be replaced?

 

Pressure or vacuum?

The EVAP system on your car should relieve any pressure buildup in the tank if it is working properly. If it is disconnected, clogged or not working properly it could cause a pressure build up in the tank.

 

completely normal to have pressure in the tank even after the car is off, it takes some time for it to bleed off