Evaporative Emissions System: Description and Operation

Evaporative Emission Control System:

Vapor Canister Except Altitude:

Fuel Pressure Control Valve:

PURPOSE
The Evaporative Emission (EVAP) control system limits fuel vapors from escaping into the atmosphere by storing the vapors in an activated carbon (charcoal) storage device (vapor canister) until the engine is able to use the extra fuel vapor.

OPERATION
The EVAP control system on uses a sealed fuel tank, a basic two tube canister, a pressure control valve and fuel/vapor hoses. The fuel tank is sealed with a fuel cap that is NOT normally vented to the atmosphere. The fuel tank cap has a safety valve which allows for both pressure and vacuum relief. Gasoline vapors from the fuel tank flow into the tube labeled "Fuel Tank". Any liquid fuel goes into a reservoir in the bottom of the canister to protect the carbon bed above. These vapors are absorbed into the carbon. The canister is purged when the engine is running above idle speed. A vacuum source is applied to the tube labeled "Canister Purge" to draw in fresh air through the bottom of the canister (open bottom). The air mixes with the vapor and is drawn into the intake manifold to be burned.