Range Rover P38
17
EMISSION CONTROL
NEW RANGE ROVER
8
DESCRIPTION AND OPERATION
Exhaust emission control.
The fuel injection system provides accurately metered
quantities of fuel to the combustion chambers to
ensure the most efficient air to fuel ratio under all
operating conditions. A further improvement to
combustion is made by measuring the oxygen content
of the exhaust gases to enable the quantity of fuel
injected to be varied in accordance with the prevailing
engine operation and ambient conditions; any
unsatisfactory composition of the exhaust gas is then
corrected by adjustments made to the fuelling by the
ECM.
The main components of the exhaust emission
system are two catalytic converters which are an
integral part of the front exhaust pipe assembly. The
catalytic converters are included in the system to
reduce the emission, to atmosphere, of carbon
monoxide (CO), oxides of nitrogen (NO
x
), and
hydrocarbons (HC). The active constituents of the
converters are platinum (Pt), palladium (PD) and
rhodium (Rh). Catalytic converters for NAS low
emission vehicles (LEVs) from 2000MY have
active constituents of palladium and rhodium
only). The correct functioning of the converters is
dependent upon close control of the oxygen
concentration in the exhaust gas entering the
catalysts.
The basic control loop comprises the engine
(controlled system), the heated oxygen sensors
(measuring elements), the engine management ECM
(control) and the injectors and ignition (actuators).
Other factors also influence the calculations of the
ECM, such as air flow, air intake temperature and
throttle position. Additionally, special driving
conditions are compensated for such as starting,
acceleration, deceleration, overrun and full load.
See
FUEL SYSTEM, Description and operation.
The reliability of the ignition system is critical for
efficient catalytic converter operation, since misfiring
will lead to irreparable damage of the catalytic
converter due to the overheating that occurs when
unburned combustion gases are burnt inside it.
CAUTION: If the engine is misfiring, it
should be shut down immediately and the
cause rectified. Failure to do so will result
in irreparable damage to the catalytic converter.
CAUTION: Ensure the exhaust system is
free from leaks. Exhaust leaks upstream of
the catalytic converter could cause
internal damage to the catalytic converter.
CAUTION: Serious damage to the engine
may occur if a lower octane number fuel
than that which is recommended is used.
CAUTION: Only unleaded fuel must be
used on vehicles fitted with catalytic
converters; serious damage to the
catalytic converter and oxygen sensors will occur
if leaded fuel is used. A reminder label is adhered
to the inside of the fuel filler flap. As a further
safeguard, the filler neck is designed to
accommodate only unleaded fuel pump nozzles.
The oxygen content of the exhaust gas is signalled to
the Engine Control Module (ECM) by two Heated
Oxygen Sensors (HO2S) located in the exhaust front
pipes, upstream of each catalytic converter. The ECM
can then make an appropriate adjustment to the fuel
supply to correct the composition of the exhaust
gases.
North American Specification (NAS) vehicles have
additional Heated Oxygen Sensors, positioned
downstream of each catalytic converter. The ECM
uses the signals from these sensors to determine
whether the catalysts are working efficiently.
