I recently replaced the two vapor/check valves on top of the gas tank (and the rubber grommets) because one of the rubber grommets was badly deteriorated, allowing fumes to escape (and gas, when the tank was topped off). After that, the noticeable gas odor I had smelled at the back of the vehicle was absent. However, after about a week, I started to detect the smell of gas fumes again, but not as much as before (and sometimes a little inside the cabin). Then, when at the gas station to gas up (the tank had been filled about 3/4 of the way and was nearly on empty at this point), a long, pronounced exhalation of air escaped from the tank, through the fill hose, when I removed the cap. I've never had that much air come out for that long.

I'm wondering if I might have, while reattaching the gas tank, crimped one of the hoses that goes from the charcoal canister to one of the valves on top of the tank? Would that keep the tank from being vented? However, now that I think about it, if the tank isn't vented, then wouldn't air rush INTO the tank when I remove the cap? (After filling up and then using most of the gas.)

Any ideas of what might be causing this? Thanks in advance for your thoughts and suggestions.

1996 Cherokee Sport, 2 door, 4.0 L HO, 5 speed manual