Discovery 2. Manual — part 452

EMISSION CONTROL - V8

DESCRIPTION AND OPERATION

17-2-7

1 Engine Control Module (ECM)
2 SAI vacuum solenoid valve
3 Purge valve
4 Vacuum reservoir
5 SAI control valve (2 off)
6 SAI pump
7 SAI pump relay
8 Main relay

EMISSION CONTROL - V8

17-2-8

DESCRIPTION AND OPERATION

Secondary air injection system control
diagram

1 Fuselink 2 (engine compartment fusebox)
2 SAI pump relay
3 SAI pump
4 SAI vacuum solenoid valve (grey harness

connector)

5 Engine Control Module (ECM)

6 Battery
7 Fuse 13 (engine compartment fusebox)
8 Inertia switch
9 Main relay

9

M17 0207

1

2

3

4

5

7

6

8

EMISSION CONTROL - V8

DESCRIPTION AND OPERATION

17-2-9

Emission Control Systems

Engine design has evolved in order to minimise the emission of harmful by-products. Emission control systems are
fitted to Land Rover vehicles which are designed to maintain the emission levels within the legal limits pertaining for
the specified market.

Despite the utilisation of specialised emission control equipment, it is still necessary to ensure that the engine is
correctly maintained and is in good mechanical order so that it operates at its optimal condition. In particular, ignition
timing has an effect on the production of HC and NO

x

emissions, with the harmful emissions rising as the ignition

timing is advanced.

CAUTION: In many countries it is against the law for a vehicle owner or an unauthorised dealer to modify or
tamper with emission control equipment. In some cases, the vehicle owner and/or the dealer may even be
liable for prosecution.

The engine management ECM is fundamental for controlling the emission control systems. In addition to controlling
normal operation, the system complies with On Board Diagnostic (OBD) system strategies. The system monitors and
reports on faults detected with ignition, fuelling and exhaust systems which cause an excessive increase in tailpipe
emissions. This includes component failures, engine misfire, catalyst damage, catalyst efficiency, fuel evaporative
loss and exhaust leaks.

When an emission relevant fault is determined, the fault condition is stored in the ECM memory. For NAS vehicles,
the MIL warning light on the instrument pack will be illuminated when the fault is confirmed. Confirmation of a fault
condition occurs if the fault is still found to be present during the driving cycle subsequent to the one when the fault
was first detected.

+

ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine

management.

The following types of supplementary control system are used to reduce harmful emissions released into the
atmosphere from the vehicle:

1 Crankcase emission control – also known as blow-by gas emissions from the engine crankcase.
2 Exhaust emission control – to limit the undesirable by-products of combustion.
3 Fuel vapour evaporative loss control – to restrict the emission of fuel through evaporation from the fuel

system.

4 Fuel leak detection system (NAS only) – there are two types of system which may be used to check the

evaporative emission system for the presence of leaks from the fuel tank to purge valve.

a Vacuum leak detection test – checks for leaks down to 1 mm (0.04 in.) in diameter.

b Positive pressure leak detection test – utilises a leak detection pump to check for leaks down to 0.5 mm (0.02

in.) in diameter.

5 Secondary air injection system (NAS only) – to reduce emissions experienced during cold starting.

Crankcase emission control system

The concentration of hydrocarbons in the crankcase of an engine is much greater than that in the vehicle's exhaust
system. In order to prevent the emission of these hydrocarbons into the atmosphere, crankcase emission control
systems are employed and are a standard legal requirement.

The crankcase ventilation system is an integral part of the air supply to the engine combustion chambers and it is
often overlooked when diagnosing problems associated with engine performance. A blocked ventilation pipe or filter
or excessive air leak into the inlet system through a damaged pipe or a leaking gasket can affect the air:fuel mixture,
performance and efficiency of the engine. Periodically check the ventilation hoses are not cracked and that they are
securely fitted to form airtight connections at their relevant ports.

The purpose of the crankcase ventilation system is to ensure that any noxious gas generated in the engine crankcase
is rendered harmless by complete burning of the fuel in the combustion chamber. Burning the crankcase vapours in
a controlled manner decreases the HC pollutants that could be emitted and helps to prevent the development of
sludge in the engine oil as well as increasing fuel economy.

EMISSION CONTROL - V8

17-2-10 DESCRIPTION AND OPERATION

A spiral oil separator is located in the stub pipe to the ventilation hose on the right hand cylinder head rocker cover,
where oil is separated and returned to the cylinder head. The rubber ventilation hose from the right hand rocker cover
is routed to a port on the right hand side of the inlet manifold plenum chamber where the returned gases mix with the
fresh inlet air passing through the throttle butterfly valve. The stub pipe on the left hand rocker cover does not contain
an oil separator, and the ventilation hose is routed to the throttle body housing at the air inlet side of the butterfly valve.
The ventilation hoses are attached to the stub pipe by metal band clamps.

Exhaust emission control system

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 catalytic 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 catalyst.

The two catalytic converters are shaped differently to allow sufficient clearance between the body and transmission,
but they remain functionally identical since they have the same volume and use the same active constituents.

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.

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 gas 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 recommended is used.
Serious damage to the catalytic converter and oxygen sensors will occur if leaded fuel is used.

Air : fuel ratio
The theoretical ideal air:fuel ratio to ensure complete combustion and minimise emissions in a spark-ignition engine
is 14.7:1 and is referred to as the stoichiometric ratio.

The excess air factor is denoted by the Lambda symbol

λ

, and is used to indicate how far the air:fuel mixture ratio

deviates from the theoretical optimum during any particular operating condition.

l

When

λ

= 1, the air to fuel ratio corresponds to the theoretical optimum of 14.7:1 and is the desired condition for

minimising emissions.

l

When

λ

> 1, (i.e.

λ

= 1.05 to

λ

= 1.3) there is excess air available (lean mixture) and lower fuel consumption can

be attained at the cost of reduced performance. For mixtures above

λ

= 1.3, the mixture ceases to be ignitable.

l

When

λ

< 1, (i.e.

λ

= 0.85 to

λ

= 0.95) there is an air deficiency (rich mixture) and maximum output is available,

but fuel economy is impaired.

The engine management system used with V8 engines operates in a narrower control range about the stoichiometric
ideal between

λ

= 0.97 to 1.03 using closed-loop control techniques. When the engine is warmed up and operating

under normal conditions, it is essential to maintain

λ

close to the ideal (

λ

= 1) to ensure the effective treatment of

exhaust gases by the three-way catalytic converters installed in the downpipes from each exhaust manifold.