Evaporative Emissions System: Description and Operation

EVAP Component Locations:

PURPOSE
The evaporative emission control system prevents the escape of fuel tank vapors into the environment. The EVAP system consists of:

^ Liquid-vapor separator (expansion tank)
^ Charcoal cannister
^ Purge valves (two)
^ Fuel storage tank and non-vented filler cap

Fig. 41 Expansion Tank/Hose Routing:

OPERATION

Liquid-vapor Separator
When the engine is OFF, fuel vapors are collected in the fuel-vapor separator (expansion tank). Most of the fuel vapor condenses into liquid and flows back to the fuel tank. The liquid-vapor separator also allows for expansion of fuel in a full tank where temperatures may vary as much as 80° F. This is necessary because the fuel tank has no direct vent to the atmosphere.

Charcoal Cannister
Excess fuel vapors are absorbed by the charcoal cannister. The charcoal cannister is equipped with a filter in the bottom surface to allow fresh air to draw through the cannister during purging.

Purge Valve Locations:

Purge Valves
When the engine is started, DME controls the purge valves allowing cannister purging based on the following inputs:

^ Coolant temperature
^ Engine speed
^ Engine load

Purging. Coolant temperature above threshold, closed loop system functioning and/or engine load above threshold.
No purging. Coolant temperature below threshold, closed loop system inactive and/or engine load below threshold.