Evaporative Emissions System: Description and Operation

FUEL TANK EVAPORATIVE CONTROL
The specification for certain countries requires the recycling of fuel evaporation from the fuel tank. For these countries only, a charcoal canister and purge valve are installed in the engine compartment.

Evaporative Purge System:

EVAPORATIVE PURGE SYSTEM
1. Charcoal canister
2. Purge valve
3. Charcoal canister air vent
4. Fuel purge connection from separator/expansion tank
5. Plenum chamber connection


OPERATION
When the engine is not running, the purge valve (2) seals the plenum chamber connection (5). Any vapor entering the canister at (4) from separator/expansion tank, is condensed by the air entering at (3) which is then absorbed by the charcoal.

The opening of the purge valve (2), which is controlled by the fuel injection engine control module (ECM), occurs when the following conditions prevail:

- When the engine is running at speeds above 1700 rpm and temperatures above 54°C (129°F), the ECM will hold open the purge valve as necessary.

- At speeds below 1700 rpm, the ECM will only pulse the purge valve open for short periods.

While the purge valve (2) is open, engine depression draws air through vent (3) and fuel tank fumes via (4) into the engine combustion chambers, where they are burned. Air entering at (3), passes through the charcoal, where any accumulation of condensed fuel is also extracted and burned in the engine.

A permanent leakage of air into the plenum chamber through the purge system will effect engine performance.

Evaporative Emission System Defender 90:

FUEL TANK EVAPORATIVE CONTROL SYSTEM
1. Fuel expansion tank
2. Relief valve to atmosphere
3. Fuel tank vent
4. Relief valve to charcoal canister
5. Charcoal canister in engine compartment
6. Fuel tank

OPERATION
The system consists of a fuel separator/expansion tank located at a higher level than the fuel tank, between the inner body side and the right rear fender. The tank is vented to atmosphere through a relief valve and is connected to the fuel tank and the charcoal canister purge system in the engine compartment.

As the temperature rises, fuel vapor in the fuel tank is allowed to vent into the separator/expansion tank (1) via three pipes and a manifold connector (3). Any vapor which condenses into liquid fuel drains through pipe (6) back into the main fuel tank and residual vapor is dealt with by the purge system connection (4) in the engine compartment.

The atmosphere relief valve (2) will only open if a blockage occurs in the charcoal canister or purge system.