Evaporative Emissions System: Description and Operation

Purge Control System Diagram:

PURPOSE
The evaporative control system prevents the escape of fuel vapors from the fuel tank and fuel injection into the atmosphere.

BASIC OPERATION
Vapors generated in the fuel tank enter the charcoal canister where the charcoal absorbs and stores the fuel vapor.

When the ECM senses the correct conditions for operation, it supplies the ground circuit to the solenoid. This opens the solenoid, allowing manifold vacuum to be applied to the carbon canister, allowing fresh air is to be drawn into the bottom of the canister.

The vapors then pass through the solenoid valve into the intake manifold to be consumed in the combustion process.

OPERATING CONDITIONS
The canister is purged (solenoid energized) under the following conditions:

Condition 1
Engine temperature above 158° F (70° C).
For the first three minutes after starting engine.
Engine rpm over 3000

Condition 2
Engine temperature above 158° F (70° C).
After three minutes of engine operation, the canister will be purged intermittently.
Engine rpm over 3000

Condition 3
Engine temperature above 158° F (70° C).
Altitude above 7,200 ft. (2,200 m).
Engine rpm over 3000

Condition 4
Engine temperature above 158° F (70° C).
Intake air temperature is above 122° F (50° C).
Engine rpm over 3000