Evaporative Emissions System: Description and Operation

Evaporative Emission Control System Schematic:

PURPOSE
The evaporative emission control system is used to prevent emission of hydrocarbons into the atmosphere.

OPERATION
The vapors generated in the fuel tank while driving or when the engine is at a stop enter the charcoal canister where the charcoal absorbs and stores the fuel vapor.

When the throttle valve opens off idle the canister is purged by manifold vacuum opening the purge control valve which in turn draws air through the filter at the bottom of the canister. The vapors then pass through the purge control valve and into the intake manifold to be consumed in the combustion process.

While the engine is running (under all throttle conditions) a small amount of the vapors are drawn into the manifold through the constant purge orifice.