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 the engine is started, the primary main fuel cut-off solenoid valve opens, allowing manifold vacuum to the purge control valve and the vacuum holding solenoid valve. Vacuum is sent to the air vent cut-off diaphragm so it will open and vent the float bowls. When the engine is warm, the thermo switch opens and operates the purge control solenoid, vacuum flows to the canister purge diaphragm, and air is drawn through to purge the canister. On Accord and Prelude models, the by-pass solenoid valve opens when the engine is warm, so tank vapors bypass the 2-way valve and move directly to the canister. See Figure.