Evaporative Emissions System: Operation

When gasoline and vapor in the fuel tank expand, they force open the 2-way valve. Liquid fuel is separated and returned to the tank, while vapors pass to the canister and are absorbed by the charcoal filter. Excess air is vented to the atmosphere.

When engine is started, the primary main fuel cut-off solenoid valve opens, allowing manifold vacuum to purge control valve and vacuum holding solenoid valve. Vacuum is sent to air vent cut-off diaphragm so it will open and vent the float bowls. When engine is warn, the thermoswitch opens and operates the purge control solenoid; vacuum flows to canister purge diaphragm and air is drawn through to purge the canister. See Figure.