Evaporative Emissions System: Testing and Inspection

Fig. 1 Evaporative emissions control system:

Fig. 2 Vapor canister:

The evaporative emission control system, Fig. 1, transfers vapors from the fuel tank to a charcoal storage tank and holds vapors when the vehicle is not operating. When the motor is idling, the fuel vapor is removes from the carbon element by the intake air flow and consumed in the combustion process.
The purge valve Fig. 2 is an integral part of the canister. When the engine is operating, carburetor ported vacuum is applied to the diaphragm which opens the valve. The lower tube on the purge valve is connected to a timed port above the throttle body injection valve. The fuel vapor purge is controlled through this port by throttle position.