Fuel tank pressure?

[Reason]

I was just thinking the other day how my 97GT would release pressure at the fuel cap whenever I took it off to fill up. But my 98L doesn't seem like its under and pressure. Is there a reason for them being how they are? Should my current car have pressure? Bad gas cap maybe?

[StatGSR]

gas tank pressure is supposed to purge through the charcoal canisiter system and fumes are supposed to be vented to engine during start up.

it is normal for the tank to build up pressure, but it shouldn't vent to anywhere besides the charcoal system. the check valve in that system could be stuck closed.

[winston856]

I wondered about this myself, so the tank is supposed to build pressure?

When I go to fill up my tank's usually run way down, I put at least 13.5 gals in it. When I open the cap there's about 2-5 seconds of air rushing out, like I'm letting air out of a tire.

Is that normal? It seems to vary from time to time in length.

[jey]

If you hear air rushing out when you open the gas cap then there is something wrong with your purge system, it is not supposed to happen. If probably only happens hen you've run the tank way down since that's when the difference in pressure becomes the greatest.

[winston856]

Any ideas what component to troubleshoot first? Are there any known or likely components of the EVAP system that would let this situation happen?

Just looking for some direction here.

[jey]

Start be looking at the condition of the lines in the evap system. I've seen evap solenoids fail too, so you can check that out.