Evaporative Emissions System: Description and Operation

Evaporative Control Canister And Valve:

PURPOSE
The evaporative control system prevents gasoline vapors from escaping into the atmosphere. Vapors from the gas tank are routed to the evaporative control canister. Carbon in the canister stores the gasoline vapors until the engine is started. The intake manifold vacuum of the running engine draws the vapors trough the EVAP valve into the combustion chamber.

LOCATION
The purge control valve is mounted to the top of the EVAP canister. The canister is mounted in the engine compartment, forward of the left front wheel housing.

CONSTRUCTION
The evaporative control system consists of a charcoal canister (which contains activated charcoal), purge valve, roll-over valve and connecting hoses.

OPERATION
The evaporative control system controls pressure variations within the gas tank resulting from changes in fuel volume and temperature. The EVAP purge valve controls the fuel vapors going to the intake manifold. The EVAP valve is controlled by an electronic control unit and the throttle valve upstream vacuum.


When the engine is idling, the EVAP valve is closed. Fuel vapor is absorbed by the activated charcoal in the canister. As engine speed increases, upstream vacuum also increases, opening the EVAP valve. This allows gasoline vapors to be drawn into the combustion chamber. The EVAP valve opens only when engine has reached operating temperature.