Gas Pressure?

I usually leave my car running when I fill it up with gas. I noticed that when I take the gas cap off, a bunch of air shoots out. If I wasn't holding the gas cap, the air would probably blow it off. Is this supposed to happen?
Thanks
Tim

[Litton]

yep, mine does the same thing. You really notice it if you pull a fuel line without properly removing gas pressure.

I think it has to do with the vapor emission requirements.

[Tomguy]

Originally posted by Tim's__Benz
I usually leave my car running when I fill it up with gas.

Isn't that illegal? Besides, if you think the cap blows off with pressure in that case, imagine what would happen if a spark went in there

[Litton]

Sparks are not a good thing in the gas tank. I don't have my book in front of me, but I think there is a vent line that goes under the car someplace and the gas cap is like a radiator cap with a pressure release built in. Come to think of it, when I have my smog check done, one of the items they check is the gas cap pressure release.

[psfred]

Some pressure is normal. Should vent through the small plastic tank somewhere in the trunk (don't remember where at the moment) and the charcoal canister under the passenger side near the rear door. Check for a plugged vent here -- I wouldn't be surprised to find it blocked with ice. Mud daubers like them, too, so do spiders.

Peter

[Tomguy]

Peter: The tank is in the pass side of the trunk, behind the "cardboard" (whatever that paper stuff is called). The spare tire has to be removed to access it.