Fuel vapors trapped in the sealed fuel tank are vented through the orifice vapor valve assembly in the top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the carbon canister for storage until they are purged to the engine for burning.
Purging the carbon canister removes the fuel vapor stored in the carbon canister. The fuel vapor is purged via a purge port system, where the vapors flow from the carbon canister to the throttle body or via an EEC-IV controlled system, where the flow of vapors from the canister to the engine is controlled by a purge solenoid or vacuum controlled purge valve. Purging occurs when the engine is at operating temperature and, in most systems, off idle.
The evaporative emission control system consists of the carbon canister, fuel tank vapor orifice and rollover valve assembly, purge control valve and/or purge solenoid valve and the pressure/vacuum relief valve.