Discovery 2. Manual - part 53

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 (up to 2003 model year 

location shown)

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 (Where fitted) – to reduce emissions experienced during cold starting.

EMISSION CONTROL - V8

17-2-10 DESCRIPTION AND OPERATION

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.

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.