Fuel evap canister on 01 Nissan Sentra.

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So I been noticing raw fuel over from back side of car where fuel cap is located. I found that the evap canister is in same location behind back quarter panel. Can a bad gas cap cause pressure build up making the canister release fuel vapor? It is the original gas cap. This I know for sure.
 
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I agree with Silverado12, your gas cap is fine and there is something wrong with the purge or vent valve (or both).

Got any codes? 2001 should have fairly standard EVAP diagnostics. The conditions required for the EVAP diagnostic to run can sometimes be tricky depending on your driving cycle, so if you have a scan tool see if there are any pending codes, not just active ones.

Do you notice the raw fuel smell all the time, or only when you are or just recently fueled up?
 
I only ever notice the smell of raw fuel occasionally after I park the car in my garage. I smell it by where the fuel door is under the wheel well. I that the evap mechanism is right there in the same area and someone told me that if the gas cap is old…which it is from 2001, that it may not be venting properly causing the evaporator to burp out the fumes. Is that a possibility? Also, I only notice this occassionaly, and its when it is hot outside.
 
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The vapor canister is part of a closed system and should not vent to the atmosphere. The gas vapors in the canister are supposed to vent into the engines intake system when driving. The problem you describe is frequently caused by people over filling the fuel tank by continual trying to top-off the gasoline tank rather than shutting off at the first or second click. I suspect your canister needs to be replaced and the vent valve checked. Ed
 
I'm not doubting what you say is true. you guys know a lot more about cars than I do. but strangely, this evap canister that is shaped like a big plastic box has a round drain tube or vent of some nature coming out of it and angling down toward the ground. So it has to be there to release something right?
 
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