Fuel Evaporation System: Operation
As fuel expands in tank, fuel laden vapors are forced out of tank through an upper vent port. Vapors flow up from fuel tank vent lines into a left and a right expansion tank.
Fuel vapors then flow from an upper vent port on expansion tank (from gravity vent valves) through a control valve, and into the charcoal canister where they are absorbed until manifold vacuum pulls them out of canister for burning.
When the engine is running above idle, a vacuum signal opens control valve and canister vapors are drawn from canister through control valve and into intake manifold for burning.