Gas Tank Pressure??

jadcock · May 10th, 2003, 06:30 PM

Okay, this should be an easy one. While I'm getting a few things done on the truck, I thought I'd ask about this as well. When I remove the gas cap on an empty tank, it REALLY has a lot of built-up pressure. It's pressure, not vacuum. It blows out around the cap when I take it off and I can smell heavy gas fumes. Do I need a new gas cap? Is a purge or return line blocked? I figure this is an easy question to answer...I just don't know the answer.

Thanks guys,

CarGuy · May 11th, 2003, 11:38 AM

Jadcock – I know that the gas tank holds pressurized fuel vapors, and probably more are present when there is less gas. I’m not familiar with all systems, but there should be a vapor line running from the fuel tank that transports fuel vapors to a charcoal canister. The vapors are held there by the charcoal in the canister and then pulled into the motor when started. I get a lot of pressurized air with my truck too – more so than my other cars. However, I don’t recall a really heavy smell of fumes. I wonder if you need a new canister or something within that system. You may be able to find something in your Haynes manual in the fuel system chapter. I’ll be doing some things with my truck today – so I’ll check mine too. HTH

jadcock · May 11th, 2003, 05:24 PM

Thanks CarGuy. I get some "pressure" on my other car too, but not like this. The hissing lasts for several seconds and I can actually hear the tank "pop" back into place...like it's ballooned out or something. I think I'm going to start releasing the pressure via the cap a few times each tankful so I don't get SO MUCH pressure built-up, until I can find the problem. I'll surf through my Haynes book to see if I can find the culprit.

aaronford · May 11th, 2003, 09:27 PM

Evap Cannister thread

Check this thread and see if any of it pertains to you. This guy found that the evap return line had fallen from its clip and was immersed in fuel causing all sorts of problems. I would suggest blowing out the evap line and checking your charcoal cannister. If you need a cannister, check with this guy as it sounds like he has an extra. Your fuel cap should hold pressure and release on vacuum, so that should not be a problem here. Let me know what you find. Aaron

jadcock · May 12th, 2003, 10:42 AM

Thanks much Aaron. I'll print this off when I get home and check it out.