Evaporative Emissions System: Description and Operation

This system is designed to minimize the amount of raw fuel vapors escaping into the atmosphere, and consists of a charcoal canister, a vapor purge control system and a fuel tank vapor control system.
The charcoal canister is used as a temporary storage facility for fuel vapors, until they can be purged from the canister into the engine where the vapors are burned.
The vapor purge control system accomplishes canister purging by drawing fresh air through the canister and into a port on the throttle body. This ported vacuum is controlled by the purge control valve. On Legend models, when coolant temperatures are above 131°F (158°F on automatic transmission vehicles), a thermovalve directs manifold vacuum to the purge control valve. When temperatures are below those specified, the thermovalve cuts vacuum to the control valve. On Integra models, when coolant temperatures are above 149°F, a purge cut-off solenoid valve controlled by the ECU directs manifold vacuum to the purge control valve. At temperatures below those specified, the cut-off solenoid cuts vacuum to the control valve.
The fuel tank vapor control system regulates the flow of fuel vapor to the canister. On Legend models, a fuel cut-off valve located at the top of the fuel tank and a liquid/vapor separator pipe, prevent liquid fuel from entering a two-way valve. On all models, when fuel vapor pressure in the tank is higher than the set value of the two-way valve, the valve opens and regulates the flow of fuel vapor into the canister.