Fuel Evaporation System: Operation
When engine is not running, fuel vapor from tank vents through check and relief valve, evaporator valve, or tank pressure control valve, depending on model, into charcoal canister. On carbureted models, the vent switching valve opens to allow carburetor vapor to vent to charcoal canister. Purge control valve is closed when engine is not running.
When engine is running, vent switching valve closes by solenoid action (if equipped). Any vacuum in fuel tank exceeding .2-.6 in. Hg will open relief side of check and relief valve (if equipped) to atmosphere. Purge control valve opens on vacuum signal from distributor advance mechanism and allows canister vapor to be drawn into intake manifold.
On Impulse, purge control valve opens when vacuum acting on purge control valve is 7.1-8.7 in. Hg on 2.3L engine, or 2.8-4.4 in. Hg on 2.0L turbo engine. When valve is opened, vapor is drawn into intake manifold.