Evaporative Emission Control System Operation
The basic Evaporative Emission (EVAP) control system used is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon (charcoal) storage canister which holds the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake airflow and consumed in the normal combustion process.
Gasoline vapors from the fuel tank flow into the tube labeled TANK. These vapors are absorbed into the carbon. The canister is purged by Engine Control Module (ECM) when the engine has been running for a specified amount of time. Air is drawn into the canister and mixed with the vapor. This mixture is then drawn into the intake manifold.
The ECM supplies a ground to energize the EVAP emission canister purge solenoid valve. This valve is Pulse Width Modulated (PWM) or turned on and off several times a second. The EVAP emission canister purge PWM duty cycle varies according to operating conditions determined by mass airflow, fuel trim, and intake air temperature.
Poor idle, stalling, and poor driveability can be caused by the following conditions:
An inoperative EVAP canister purge valve.
A damaged canister.
Hoses that are split, cracked, or not connected to the proper tubes.
Evaporative Emission Canister
The evaporative emission (EVAP) canister is an emission control device containing activated charcoal granules. The evaporative emission canister is used to store fuel vapors from the fuel tank. Once certain conditions are met, the Engine Control Module (ECM) activates the EVAP canister purge solenoid, allowing the fuel vapors to be drawn into the engine cylinders and burned.
Thursday, April 22nd, 2010 AT 4:20 AM