Evaporative Emissions System: Description and Operation

EVAP System:

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

^ Gravity float valve
^ Charcoal cannister
^ Purge valve
^ Fuel storage tank (fuel cell), and non-vented filler cap

Fuel Tank View:

OPERATION

Fuel Tank
The "Hump" section of the plastic fuel cell (fuel tank), 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. An exterior liquid-vapor separator is not needed.

Float Gravity Valve Location:

[1][2]Float Gravity Valve
The float gravity valve prevents fuel from flowing to the charcoal canister due to accident or excessively high tank pressures.

Charcoal Canister Location:

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 Valve
When the engine is started, DME controls the purge valve 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.