It seems like every time I open my gas tank to fill up there is a lot of extra pressure inside escaping. It happens whether I've been driving for a minute or an hour. Is this normal or is something not working correctly to let out the pressure?

Also, what is the charcoal chamber that I've heard about? and does it have to do with this?

 

Pressure in the fuel tank is normal. It is regulated by the tank pressure control valve - part of the EVAP canister purge control. There is also a secondary pressure relief valve in teh fuel filler cap to relieve pressure in case of failure of the tank pressure control valve. I have not been able to determine what the actual pressure limits of these vales might be, but it isn't very high (lower than 4-5 PSIG).

The EVAP (evaporative emissions control) canister is the charcoal canister you are asking about. It allows air and fuel vapors from the tank to ventilate through the charcoal medium. Fuel is trapped in the porous carbon (charcoal) medium and air is allowed to vent to atmosphere. When the engine is running at part throttle and light loads, the purge valve on the canister is opened and fuel vapors are admitted to the intake to be burned normally, rather than allowed to escape and pollute the air. It's also a good way to maintain better fuel economy, since part of the fuel you pay for doesn't just evaporate.

Anything else we can help you with today?

 

Awesome answer! I think the owner before me lost his filler cap because all i ahve now is a plastic on, no valve that i have noticed. Would it be better to pick up a different one?

Also, is the charcoal canister the plastic ball under the driver side turn signal? If not, what is that? I just got a digital camera today s i'll take a picture of it tonight if no one knows what i'm talking about already.