Evaporative Emissions System: Description and Operation

Evaporative Emission Control System Schematic:

SYSTEM DESCRIPTION

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.

Vapor Canister:

VAPOR CANISTER

Gasoline vapors from the fuel tank flow into the tube labeled "TANK". These vapors are absorbed into the carbon. The canister is purged when the engine is warm and running above idle speed. Ambient air is allowed into the canister through the filter at the bottom. The air mixes with the vapor and is drawn into the intake manifold to be burned.

Purge Valve Circuit Diagram:

EVAPORATIVE CONTROL

The PCM operates a normally closed solenoid valve, which controls vacuum to the purge passage in the charcoal canister. Normally the solenoid is turned "OFF", preventing canister purge. The PCM completes the circuit to ground, turning the solenoid "ON" when the following conditions exist:

1. Engine is at normal operating temperature.
2. Engine has been running a specified time.