Where is the fuel vapor charcoal canister located?

I was told this was most likely the problem. When I run the engine it develops a negative pressure within the tank and also it keeps shutting the fuel nozzle off at the pump. When I remove the gas cap it is suctioned on to the filler neck. I have tried replacing the gas cap with no luck. Does it sound like this is the problem? If so, where is it and how do I replace it? Thank you.