when my gas tank is near empty and i open the gas cap, there is a fair amount of air that seems to be sucked into the gas tank. is this due to a bad gas cap?
thanks

 

That's due to a good gas-cap. Means you're not letting any vapors out.

 

Lol... There should be a vacuum on a fuel tank with properly functioning evaporate system. The vapors are sucked into the engine while running to reduce atmospheric pollution from evaporating gas.

 

ha. sweet. i guess i just haven't heard or noticed that suction sound from other cars and gas tanks.
thanks!

 

It's not an always thing... some cars will pop a check engine light if you open the gas cap while the car is on.

 

It was nearly impossible to remove the gas cap off of our car. I twisted it, but I had a difficult time actually pulling it off, and when it did come off, it made a whoosh (suction?) sound. Is it possible that there was enough vacuum in the system to make removing the gas cap difficult? What would cause this vacuum? We have never experienced this before.

 

I had some vacuum hoses changed at the mechanic. Now the vacuum suction coming from the gas tank has disappeared. ie when I open the gas tank, there is no longer the suction sound. I'm assumed this was directly related and so I brought it back to the mechanic. He said he "smoke tested" the system and there were no leaks. Any suggestions? I would imagine there's a vacuum hose that's still disconnected somewhere or has a leak.
Thanks a lot!

 

After following some of the vacuum lines I saw that one wasn't even connected to the canister in front of the driver's tire. I replaced some of the connections with simple tubing from the local auto parts store and got that suction sound back at the gas cap indicating a good seal on the vacuum system. One of the connectors that was crumbling away was just behind the fuel filter (towards the back of the car on the passenger side).
To remove the canister in front of the drivers tire you remove the bolt and push the canister up about an inch to release it from a hook it is sitting on. Makes the tube replacement possible.

The first picture is the connection just behind the fuel filter. You can see the schrader valve at the top of the photo.
The second picture is the canister that is just in front of the drivers sided front tire. I taped one of the tubes blue to make sure it went to the right spot though I'm not sure it makes a difference.