Fuel Evaporation System: Notes

NOTE: For fuel evaporation system component identification, refer to illustration. See Figure.

The Evaporative (EVAP) emission control system limits fuel vapor emissions to the atmosphere. The EVAP system transfers the fuel vapor from a sealed fuel tank to an activated carbon (charcoal) storage device (EVAP canister). The EVAP canister will store the fuel vapors until the engine is able to use them. When the engine is able to use the extra fuel vapor, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process. The enhanced Evaporative (EVAP) emission system is required to detect evaporative fuel system leaks as small as 0.040" (1 mm) between the fuel filler cap and the purge valve. The system can test the evaporative emission system integrity by applying a vacuum signal, ported or manifold, to the fuel tank. This will create a small vacuum that can be monitored for leaks.