Evaporative Emissions System: Description and Operation

Evaporative Emission Control System:

PURPOSE:
To prevent the discharge of fuel vapors into the atmosphere under all operating conditions.

OPERATION:
The Evaporative Emission Control System (EECS) uses an activated carbon storage canister. Gasoline vapors from the fuel tank flow into the tube labeled "TANK." Any liquid fuel goes into a reservoir at the bottom of the canister to protect the carbon bed above. The vapors are absorbed into the carbon. When the engine is running above idle speed the canister is purged by intake air flow and consumed in the normal combustion process.

EVAP Canister Control Valve:

The EVAP canister control valve is a spring based vacuum diaphragm valve, normally closed. When the engine is running, vacuum is applied to the valve and the valve is opened. Fuel vapors from the canister are now free to flow to the manifold when the purge port is uncovered by the throttle blade.

When the engine is shut "OFF," no vacuum is applied to the valve, and the vapors are prevented from migrating to the intake manifold.