Evaporative Emissions System: Description and Operation

Evaporative Emission Control Schematic:

Purpose
To prevent the discharge of fuel vapors into the atmosphere under all operating conditions.

Charcoal Canister:

Charcoal Canister

Operation
The Evaporative Emission Control System (EECS) uses an activated carbon storage canister. Gasoline vapors from the fuel tank flow into the tube labeled "TANK." Any liquid fuel goes into a reservoir at the bottom of the canister to protect the carbon bed above. The vapors are absorbed into the carbon. When the engine is running above idle speed the canister is purged by intake air flow and consumed in the normal combustion process.


Purge Control Solenoid

Operation
The solenoid uses pulse width modulation to control purge. This means that the PCM opens and closes the solenoid many times a second.

The PCM operates a normally closed solenoid valve which controls the vacuum to purge the charcoal canister. Under cold engine or idle conditions, the valve is not energized by the PCM, which blocks vacuum to purge the EVAP canister.

The PCM energizes the solenoid valve and allows purge when:

^ The engine is warm
^ The engine has been running a specified time

Results of Incorrect Operation

Poor idle, stalling and poor driveability can be caused by:
^ Inoperative EVAP canister purge solenoid.
^ Damaged EVAP canister
^ Hoses split, cracked and/or not connected to the proper tubes.

Evidence of fuel loss or fuel vapor odor can be caused by:
^ Liquid fuel leaking from fuel lines, or fuel pump.
^ Cracked or damaged EVAP canister~
^ Disconnected, misrouted, kinked, deteriorated or damaged vapor hoses, or control hoses

If the EVAP canister purge solenoid is always open, the canister can purge to the intake manifold at all times. This can allow extra fuel at idle or during warm-up, which can cause rough or unstable idle, or too rich operation.

If the EVAP canister purge solenoid is always closed, the canister can become over-loaded, resulting in fuel odor.

Location
The fuel evaporation canister is mounted in the right front of engine compartment.

The purge control solenoid is mounted to the right side of the intake manifold.