so i have a 99 chevy blazer 2 door and when i take the cap off to put gas in it a lot of air comes out. it only started doing it this week. can any one help me on this

 

Air comes out or goes in?? The cap is supposed to vent excess pressure, but the tank is typically kept in a vacuum state by the EVAP system.

 

well i put a new pump in this week but i put in in the same way i took the other out. what is that air valve thing that is next to the tank. it has to wires going to it but it is always open. i was thanking maybe for a rollover it don't let gas out.

 

it is coming out of the tank

 

If these newer tanks and gas caps are anything like the old tanks, you just need a new gas cap. The cap SHOULD be designed to allow the tank to breath. I'm sure someone familiar with current technology will be able to come in and either confirm or deny this.

 

ok you said you replaced the fuel pump right? did you hook EVERY line back up? did you change the tank O-ring when you replaced the pump? if you did then your gas cap would definatly be the culprit.. I would go get a replacement and see if that fixes it its a cheap fix i think $10-12.

 

check the vent hoses on the tank there one all the way in front its a pain to get to and then theres one in the back corner of the tank then of course there the big one by the fill but id check that before anything

 

Ok guys, I have a question about these vent hoses-what keeps fuel from coming out of those hoses if you go over two railroad tracks side by side or even go off-roading?

 

thanks guys i put a hole in the cap i have lol so far so good if it works all day i will go out and buy a new cap...

 

ok so it did not work so now there is a code tank pressure sensor and the other is purge vent. so my ? is is there a fuse going to them.