Emission control systems

EMISSION CONTROL SYSTEMS

The vehicle is fitted with various emission and evaporative control components to comply with emission regulation requirements.

The following control systems are used to reduce harmful emissions released into the atmosphere at all times, and under all conditions:

1. Exhaust emission control
2. Fuel vapour evaporative loss control
3. Crankcase emission control

In many countries it is against the law for a vehicle owner or an unauthorised repair shop to modify or tamper with emission control equipment. In this event the vehicle owner and/or the repairer may be liable for prosecution.

The emission control system fitted to the vehicle is designed to keep the emissions within the legal limits, provided that the engine is correctly maintained and is in good mechanical condition.

Exhaust emission control

The engine management system provides accurately metered quantities of fuel to the combustion chambers, to ensure the most efficient air to fuel ratio under all conditions of operation. A further improvement to combustion is made by measuring the oxygen content of the exhaust gases. This enables the quantity of injected fuel to be varied, which allows the ratio needed for efficient gas conversion by the catalytic converter to be maintained.

The catalytic converter is situated between the exhaust front pipe and exhaust tail pipe. The catalytic converter reduces emissions of carbon monoxide, oxides of nitrigen (NOx) and hydrocarbons. The active constituents of the converter are the precious metals palladium and rhodium.

The correct operation of the catalytic converter is dependent upon close control of the oxygen concentration of the exhaust gas entering the converter. The quantity of oxygen in the exhaust gas is determined by a heated oxygen sensor situated in the exhaust manifold. The heated oxygen sensor provides the engine control module with a signal dependent on the oxygen content. The ECM can then adjust the amount of injected fuel, so that it can implement the necessary changes to achieve the correct exhaust gas content.

CAUTION: Serious damage to catalytic converter will occur if leaded fuel is used. The filler neck is designed to accommodate only unleaded fuel pump nozzles.

Evaporative emission canister

The evaporative emission (EVAP) canister is situated beneath the LH inner wing valance, and contains charcoal which absorbs and stores fuel from the fuel tank when the engine is not running. When the engine is running the vapour is purged from the canister into the engine and burned.

The EVAP canister is purged when the EVAP canister purge valve is opened. Manifold depression draws fresh air into the canister through the charcoal, which releases fuel vapour into the inlet manifold.

Evaporative emission canister purge valve

The EVAP canister purge valve is operated by the ECM. The valve remains closed until engine temperature rises above 70°C. This is to maintain engine tune and catalyst performance. If the valve was to open with the engine cold or at idling speed, the enriched mixture would delay catalyst light off time and cause erratic idling. When the purge valve opens, fuel vapour from the EVAP canister is drawn along a pipe through the valve and into the inlet manifold for combustion.