Evaporative Emissions System: Description and Operation

Evaporative Emissions (EVAP) Control System Schematic:

Purpose:
The Evaporative Emission Control System (EECS) used on this vehicle is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon storage canister. This retains the fuel vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.



Operation:

Vapor Canister:

Fuel Vapor Canister
The evaporative emission control system uses an inversely mounted 1500 cc charcoal canister to absorb fuel vapors from the gas tank.

Gasoline vapors from the fuel tank flow into the tank tube. These vapors are absorbed into the carbon. The canister is purged by PCM control when the engine has been running for a specified amount of time. Air is drawn into the canister and mixed with the vapor and then is drawn into the intake manifold.

Canister Purge Solenoid:

Evaporative Control
The PCM operates the solenoid to control vacuum to the canister. Under cold engine or idle conditions, the solenoid is closed, which prevents vacuum from being applied to the canister.

The PCM activates the solenoid valve and allows purge under the following conditions:

^ Engine is warm
^ After the engine has been running a specified period of time
^ The IAT reading is above 9.5°C (50°F)