I’ve been reading up on general evap system operation and apparently the canister vent balance is normally open to the atmosphere and closes during leak testing and when vapors are being pulled into the engine for burning.

So my question is, if it’s normally open to the atmosphere and fuel vapors are stored inside within the charcoal... do the fuel vapors not escape out to the atmosphere at all?


1 Answer 1


The canister is filled with activated charcoal, which is very effective at storing fuel vapors. Effective enough, in fact, that no fuel smell is detectable before the canister is purged by fresh air into the engine.

Well, that's the standard reason why. There are some that may argue that no fuel vapors escape because EVAP systems are totally useless... But, that's another can of worms.

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