Evaporative Emissions System: Description and Operation

Fig. 16 Operation Of The Evaporative Emission Control System:

CARBON CANISTER

While the engine is not running fuel vapors generated inside the fuel system are absorbed and stored in the carbon canister. When the engine is started once again the ECU will purge the fuel vapors from the carbon canister to the engine intake.

PURGE CONTROL VALVE

The purge control valve is a vacuum operated valve controlled by the thermo valve that permits purging of the carbon canister.

THERMO VALVE

The thermo valve is used to prevent purge system operation until the engine has warmed up (coolant temperature greater than 45 degrees C or 113 degrees F). This prevents driveability problems and excessive hydrocarbon emissions during engine warm up.

OVERFILL LIMITER VALVE

The overfill limiter consists of a pressure valve and a vacuum valve. The pressure valve is designed to open when the fuel tank internal pressure has increased over normal pressure and the vacuum valve opens when a vacuum has been produced in the tank.

BOWL VENT VALVE

The bowl vent valve is used to isolate the float bowl and the fuel vapors inside it from atmosphere when the engine is off. When the engine is operating intake manifold vacuum opens the bowl vent valve to the purge system.