Evaporative Emission Control Canister: Description and Operation

EVAP CANISTER





Fuel vapor from the tank passes a bed of activated charcoal in the EVAP Canister (3). The activated charcoal binds the fuel and pure air flows out into the atmosphere through the connector at the top of the canister. 80-140 g fuel can be bound in the canister, depending on the volume of charcoal.

Control

Normally the canister purge (CP) valve is closed and only opens when the engine control module (ECM) is emptying the canister. When the EVAP canister is emptied the valve is first pulsed, this pulsing increases to bring the mixture from the canister up to a value which varies according to engine load and speed. Because of the negative pressure in the inlet manifold, fresh air is sucked into the engine through the EVAP canister opening or through the EVAP canister shut-off valve. As the air passes through the EVAP canister, fuel stored in the activated charcoal is drawn into the engine and burned.