Evaporative Emission Control System (EVAP) Testing

NOTE: This is a non-electrical, vacuum operated system.

OPERATION
The EVAP canister is equipped with a vacuum controlled purge control valve (orifice) that controls canister purge operation. The control valve is open when engine manifold vacuum is applied to it. When the engine is operating, the EVAP canister purge function draws fresh air through the top of the canister. This causes the stored vapors to be drawn out of the canister and into the airstream in the air cleaner housing snorkel.

The air cleaner contains a venturi in the air cleaner cover used as a purge line vacuum source. The venturi effect increases the speed of the intake air flowing by the slots in the venturi wall. This creates a low pressure area around the slots. When the purge control valve is open, vapors from the canister are drawn through slots and into the stream flowing through the venturi.

The fuel vapors then pass through the intake manifold and into the engine combustion chambers. Here they are consumed during engine combustion.