Pressurized gas tank - what gives?
 

My car runs fine, but when I fill up the tank hisses and I can see distortion on the grond from the vapor. That's why I think it's pressurized rather than under vacuum. What's up?

okay, so i filled up today and it's definitely pressurized - not a vacuum. any idea what would cause this?

blocked breather,

if get under the car inbetween the diff and fuel tank on the floor pan you will see a valve and a line that wiggles its way around the floor pan, this is the breather, make sure it isnt blocked or crushed, this also goes to the charcol canaster,

Dale

okay, so is it an emissions thing that i can get from autozone, or what?

I thought they all did that: some modern emissions control thing. Shouldn't it hiss? I can't think of a car I've owned in the last 20 years that hasn't done it.

B

Read the manual. It should hold a small amount of positive or negative pressure before venting it to equalize with atmosphere. If the vent valve 10sec mentions fails, or the charcol cannister gets clogged, then itll allow excessive pos and/or neg pressure to build up.