2002 LAND ROVER DISCOVERY engine

EMISSION CONTROL - V8
17-2-32 DESCRIPTION AND OPERATION
Vacuum reservoir
1Vacuum port to SAI vacuum solenoid valve
2Vacuum port to intake manifold (one-way valve
end)
3Vacuum reservoir
A vacuum reservoir is included in the vacuum supply line between the intake manifold and the SAI vacuum solenoid
valve. The vacuum reservoir contains a one-way valve, to stop depression leaking back towards the intake manifold
side. The reservoir holds a constant vacuum so that the SAI control valves open instantaneously as soon as the SAI
solenoid valve is energised.
The vacuum reservoir is a plastic canister construction located on a bracket at the LH side of the engine compartment.
It is important to ensure the reservoir is fitted in the correct orientation, and the correct vacuum hoses are attached to
their corresponding ports. The one-way valve end of the vacuum reservoir (cap end, to inlet manifold) is fitted towards
the rear of the vehicle.
A small bore nylon hose is used to connect the one-way valve end of the vacuum reservoir to a port on the RH side
of the inlet manifold. A further hose connects between the other port on the vacuum reservoir and a port on the front
of the SAI vacuum solenoid valve.
M17 0212
1
2
3

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-33
Crankcase emission control operation
Oil laden noxious gas in the engine crankcase is drawn through a spiral oil separator 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 mass of fresh air which is drawn in from the
atmospheric side of the throttle butterfly to mix with the returned crankcase gas depends on the throttle position and
the engine speed.
1Hose – RH rocker cover to inlet manifold
2Inlet manifold
3Throttle body
4Air intake
5Hose – LH rocker cover to inlet manifold
6LH rocker cover breather tube (without oil
separator)7LH rocker cover baffle
8RH rocker cover baffle
9RH rocker cover breather tube
10Oil separator (integral with breather tube)
When the engine is running in cruise conditions or at idle, manifold pressure is low and the majority of gases are drawn
into the inlet manifold through the oil / vapour separator in the RH rocker cover stub pipe. At the same time, filtered
air is drawn from the throttle body into the engine via the LH rocker cover.
During periods of driving at Wide Open Throttle (WOT), pressure at either side of the throttle disc equalizes (manifold
depression collapses). The larger ventilation opening at the throttle housing positioned in the fast moving stream of
intake air, now offers more 'pull' than the small opening in the RH rocker cover and the flow of ventilation reverses,
drawing gases from the LH rocker cover into the throttle body for subsequent burning in the combustion chambers.

EMISSION CONTROL - V8
17-2-34 DESCRIPTION AND OPERATION
Exhaust emission control operation
The oxygen content of the exhaust gas is monitored by heated oxygen sensors using either a four sensor (NAS only)
or two sensor setup, dependent on market destination and legislative requirements. Signals from the heated oxygen
sensors are input to the engine management ECM which correspond to the level of oxygen detected in the exhaust
gas. From ECM analysis of the data, necessary changes to the air:fuel mixture and ignition timing can be made to
bring the emission levels back within acceptable limits under all operating conditions.
Changes to the air:fuel ratio are needed when the engine is operating under particular conditions such as cold starting,
idle, cruise, full throttle or altitude. In order to maintain an optimum air:fuel ratio for differing conditions, the engine
management control system uses sensors to determine data which enable it to select the ideal ratio by increasing or
decreasing the air to fuel ratio. Improved fuel economy can be arranged by increasing the quantity of air to fuel to
create a lean mixture during part-throttle conditions, however lean running conditions are not employed on closed loop
systems where the maximum is
λ = 1. Improved performance can be established by supplying a higher proportion of
fuel to create a rich mixture during idle and full-throttle operation. Rich running at wide open throttle (WOT) for
performance and at high load conditions helps to keep the exhaust temperature down to protect the catalyst and
exhaust valves.
The voltage of the heated oxygen sensors at
λ = 1 is between 450 and 500 mV. The voltage decreases to 100 to 500
mV if there is an increase in oxygen content (
λ > 1) indicating a lean mixture. The voltage increases to 500 to 1000
mV if there is a decrease in oxygen content (
λ < 1), signifying a rich mixture.
The heated oxygen sensor needs to operate at high temperatures in order to function correctly (
≥ 350° C). To achieve
this the sensors are fitted with heater elements which are controlled by a pulse width modulated (PWM) signal from
the engine management ECM. The heater element warms the sensor's ceramic layer from the inside so that the
sensor is hot enough for operation. The heater elements are supplied with current immediately following engine start
and are ready for closed loop control within about 20 to 30 seconds (longer at cold ambient temperatures less than
0
°C (32°F)). Heating is also necessary during low load conditions when the temperature of the exhaust gases is
insufficient to maintain the required sensor temperatures. The maximum tip temperature is 930
° C.
A non-functioning heater element will delay the sensor's readiness for closed loop control and influences emissions.
A diagnostic routine is utilised to measure both sensor heater current and the heater supply voltage so its resistance
can be calculated. The function is active once per drive cycle, as long as the heater has been switched on for a pre-
defined period and the current has stabilised. The PWM duty cycle is carefully controlled to prevent thermal shock to
cold sensors.
The heated oxygen sensors age with mileage, causing an increase in the response time to switch from rich to lean
and lean to rich. This increase in response time influences the closed loop control and leads to progressively
increased emissions. The response time of the pre-catalytic converter sensors are monitored by measuring the period
of rich to lean and lean to rich switching. The ECM monitors the switching time, and if the threshold period is exceeded
(200 milliseconds), the fault will be detected and stored in the ECM as a fault code (the MIL light will be illuminated
on NAS vehicles). NAS vehicle engine calibration uses downstream sensors to compensate for aged upstream
sensors, thereby maintaining low emissions.
Diagnosis of electrical faults is continuously monitored for both the pre-catalytic converter sensors and the post-
catalytic converter sensors (NAS only). This is achieved by checking the signal against maximum and minimum
threshold for open and short circuit conditions. For NAS vehicles, should the pre- and post-catalytic converters be
inadvertently transposed, the lambda signals will go to maximum but opposite extremes and the system will
automatically revert to open loop fuelling. The additional sensors for NAS vehicles provide mandatory monitoring of
the catalyst conversion efficiency and long term fuelling adaptations.
Note that some markets do not legislate for closed loop fuelling control and in this instance no heated oxygen
sensors will be fitted to the exhaust system.

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-35
Failure of the closed loop control of the exhaust emission system may be attributable to one of the failure modes
indicated below:
lMechanical fitting & integrity of the sensor.
lSensor open circuit / disconnected.
lShort circuit to vehicle supply or ground.
lLambda ratio outside operating band.
lCrossed sensors.
lContamination from leaded fuel or other sources.
lChange in sensor characteristic.
lHarness damage.
lAir leak into exhaust system (cracked pipe / weld or loose fixings).
System failure will be indicated by the following symptoms:
lMIL light on (NAS and EU-3 only).
lDefault to open-loop fuelling for the defective cylinder bank.
lIf sensors are crossed, engine will run normally after initial start and then become progressively unstable with
one bank going to its maximum rich clamp and the other bank going to its maximum lean clamp – the system will
then revert to open-loop fuelling.
lHigh CO reading
lStrong smell of H
2S (rotten eggs)
lExcessive emissions
Fuel metering
When the engine is cold, additional fuel has to be provided to the air:fuel mixture to assist starting. This supplementary
fuel enrichment continues until the combustion chamber has heated up sufficiently during the warm-up phase.
Under normal part-throttle operating conditions the fuel mixture is adjusted to provide minimum fuel emissions and
the air:fuel mixture is held close to the optimum ratio (
λ = 1). The engine management system monitors the changing
engine and environmental conditions and uses the data to determine the exact fuelling requirements necessary to
maintain the air:fuel ratio close to the optimum value that is needed to ensure effective exhaust emission treatment
through the three-way catalytic converters.
During full-throttle operation the air:fuel mixture needs to be made rich to provide maximum torque. During
acceleration, the mixture is enriched by an amount according to engine temperature, engine speed, change in throttle
position and change in manifold pressure, to provide good acceleration response.
When the vehicle is braking or travelling downhill the fuel supply can be interrupted to reduce fuel consumption and
eliminate exhaust emissions during this period of operation.
If the vehicle is being used at altitude, a decrease in the air density will be encountered which needs to be
compensated for to prevent a rich mixture being experienced. Without compensation for altitude, there would be an
increase in exhaust emissions and problems starting, poor driveability and black smoke from the exhaust pipe. For
open loop systems, higher fuel consumption may also occur.

EMISSION CONTROL - V8
17-2-36 DESCRIPTION AND OPERATION
Exhaust Emission System Diagnostics
The engine management ECM contains an on-board diagnostics (OBD) system which performs a number of
diagnostic routines for detecting problems associated with the closed loop emission control system. The diagnostic
unit monitors ECM commands and system responses and also checks the individual sensor signals for plausibility,
these include:
lLambda ratio outside of operating band
lLambda heater diagnostic
lLambda period diagnostic
lPost-catalytic converter lambda adaptation diagnostic (NAS only)
lCatalyst monitoring diagnostic
Lambda ratio outside operating band
The system checks to ensure that the system is operating in a defined range around the stoichiometric point. If the
system determines that the upper or lower limits for the air:fuel ratio are being exceeded, the error is stored as a fault
code in the ECM diagnostic memory (the MIL light is illuminated on NAS vehicles).
Lambda heater diagnostic
The system determines the heater current and supply voltage so that the heater's resistance can be calculated. After
the engine has been started, the system waits for the heated oxygen sensors to warm up, then calculates the
resistance from the voltage and current measurements. If the value is found to be outside of the upper or lower
threshold values, then the fault is processed (the MIL light is illuminated on NAS vehicles).
Lambda period diagnostic
The pre-catalytic converter sensors are monitored. As the sensors age, the rich to lean and the lean to rich switching
delays increase, leading to increased emissions if the lambda control becomes inaccurate. If the switching period
exceeds a defined limit, the sensor fault is stored in the ECM diagnostic memory (the MIL light is illuminated on NAS
vehicles).
Post-catalytic converter lambda adaptation diagnostic (NAS only)
On NAS vehicles the ageing effects of the pre-catalytic converter sensors are compensated for by an adaptive value
derived from the post-catalytic converter sensors. This is a long term adaption which only changes slowly. For a rich
compensation the additive value is added to the rich delay time. For a lean compensation, the adaptive value is added
to the lean delay time. The adaptive time is monitored against a defined limit, and if the limit is exceeded, the fault is
stored in the ECM's diagnostic memory and the MIL light is illuminated on the instrument pack.
Catalyst monitoring diagnostic
On NAS specification vehicles the catalysts are monitored both individually and simultaneously for emission pollutant
conversion efficiency. The conversion efficiency of a catalyst is monitored by measuring the oxygen storage, since
there is a direct relationship between these two factors. The closed loop lambda control fuelling oscillations produce
pulses of oxygen upstream of the catalyst, as the catalyst efficiency deteriorates its ability to store oxygen is
decreased. The amplitudes of the signals from the pre-catalytic and post-catalytic converter heated oxygen sensors
are compared. As the oxygen storage decreases, the post-catalytic converter sensor begins to follow the oscillations
of the pre-catalytic converter heated oxygen sensors. Under steady state conditions the amplitude ratio is monitored
in different speed / load sites. There are three monitoring areas, and if the amplitude ratio exceeds a threshold in all
three areas the catalyst conversion limit is exceeded; the catalyst fault is stored in the diagnostic memory and the MIL
light is illuminated on the instrument pack. There is a reduced threshold value for both catalysts monitored as a pair.
In either case, a defective catalyst requires replacement of the downpipe assembly.

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-37
In the case of a catalytic converter failure the following failure symptoms may be apparent:
lMIL light on after 2 driving cycles (NAS market only).
lHigh exhaust back pressure if catalyst partly melted.
lExcessive emissions
lStrong smell of H
2S (rotten eggs).
Oxygen sensor voltages can be monitored using 'Testbook', the approximate output voltage from the heated oxygen
sensors with a warm engine at idle and with closed loop fuelling active are shown in the table below:
Mass air flow sensor and air temperature sensor
The engine management ECM uses the mass air flow sensor to measure the mass of air entering the intake and
interprets the data to determine the precise fuel quantity which needs to be injected to maintain the stoichiometric
air:fuel ratio for the exhaust catalysts. If the mass air flow sensor fails, lambda control and idle speed control will be
affected and the emission levels will not be maintained at the optimum level. If the device should fail and the ECM
detects a fault, it invokes a software backup strategy.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
The air temperature sensor is used by the engine management ECM to monitor the temperature of the inlet air. If the
device fails, catalyst monitoring will be affected. The air temperature sensor in integral to the mass air flow sensor.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
Throttle position sensor
If the engine management ECM detects a throttle position sensor failure, it may indicate a blocked or restricted air
intake filter. Failure symptoms may include:
lPoor engine running and throttle response
lEmission control failure
lNo closed loop idle speed control
lAltitude adaption is incorrect
If a signal failure should occur, a default value is derived using data from the engine load and speed.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
Atmospheric pressure will vary with altitude and have a resulting influence on the calculations performed by the ECM
in determining the optimum engine operating conditions to minimise emissions. The following are approximate
atmospheric pressures for the corresponding altitudes:
l0.96 bar at sea level
l0.70 bar at 2,750 m (9,000 ft.)
Measurement Normal catalyst Defective catalyst
Pre-catalytic heated oxygen sensors ~ 100 to 900 mV switching @ ~ 0.5
Hz~ 100 to 900 mV switching @ ~ 0.5 Hz
Post-catalytic heated oxygen sensors ~ 200 to 650 mV, static or slowly
changing~ 200 to 850 mV, changing up to same
frequency as pre-catalytic heated oxygen
sensors
Amplitude ratio (LH HO
2 sensors & RH
HO
2 sensors)<0.3 seconds >0.6 seconds (needs to be approximately
0.75 seconds for single catalyst fault)
Number of speed/load monitoring areas
exceeded (LH & RH)0 >1 (needs to be 3 for fault storage)

EMISSION CONTROL - V8
17-2-38 DESCRIPTION AND OPERATION
Evaporative emission control operation
Fuel vapour is stored in the activated charcoal (EVAP) canister for retention when the vehicle is not operating. When
the vehicle is operating, fuel vapour is drawn from the canister into the engine via a purge control valve. The vapour
is then delivered to the intake plenum chamber to be supplied to the engine cylinders where it is burned in the
combustion process.
During fuel filling the fuel vapour displaced from the fuel tank is allowed to escape to atmosphere, valves within the
fuel filler prevent any vapour escaping through to the EVAP canister as this can adversely affect the fuel cut-off height.
Only fuel vapour generated whilst driving is prevented from escaping to atmosphere by absorption into the charcoal
canister. The fuel filler shuts off to leave the tank approximately 10% empty to ensure the ROVs are always above
the fuel level and so vapour can escape to the EVAP canister and the tank can breathe. The back pressures normally
generated during fuel filling are too low to open the pressure relief valve, but vapour pressures accumulated during
driving are higher and can open the pressure relief valve. Should the vehicle be overturned, the ROVs shut off to
prevent any fuel spillage.
Fuel vapour generated from within the fuel tank as the fuel heats up is stored in the tank until the pressure exceeds
the operating pressure of the two-way valve. When the two-way valve opens, the fuel vapour passes along the vent
line from the fuel tank (via the fuel tank vapour separator) to the evaporation inlet port of the EVAP canister. The fuel
tank vents between 5.17 and 6.9 kPa.
Fuel vapour evaporating from the fuel tank is routed to the EVAP canister through the fuel vapour separator and vent
line. Liquid fuel must not be allowed to contaminate the charcoal in the EVAP canister. To prevent this, the fuel vapour
separator fitted to the fuel neck allows fuel to drain back into the tank. As the fuel vapour cools, it condenses and is
allowed to flow back into the fuel tank from the vent line by way of the two-way valve.
The EVAP canister contains charcoal which absorbs and stores fuel vapour from the fuel tank while the engine is not
running. When the canister is not being purged, the fuel vapour remains in the canister and clean air exits the canister
via the air inlet port.
The engine management ECM controls the electrical output signal to the purge valve. The system will not work
properly if there is leakage or clogging within the system or if the purge valve cannot be controlled.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
When the engine is running, the ECM decides when conditions are correct for vapour to be purged from the EVAP
canister and opens the canister purge valve. This connects a manifold vacuum line to the canister and fuel vapour
containing the hydrocarbons is drawn from the canister's charcoal element to be burned in the engine. Clean air is
drawn into the canister through the atmosphere vent port to fill the displaced volume of vapour.
The purge valve remains closed below preset coolant and engine speed values to protect the engine tune and
catalytic converter performance. If the EVAP canister was purged during cold running or at idling speed, the additional
enrichment in the fuel mixture would delay the catalytic converter light off time and cause erratic idle. When the purge
valve is opened, fuel vapour from the EVAP canister is drawn into the plenum chamber downside of the throttle
housing, to be delivered to the combustion chambers for burning.
The purge valve is opened and closed in accordance with a pulse width modulated (PWM) signal supplied from the
engine management ECM. The system will not work properly if the purge valve cannot be controlled. Possible failure
modes associated with the purge valve are listed below:
lValve drive open circuit.
lShort circuit to vehicle supply or ground.
lPurge valve or pipework blocked or restricted.
lPurge valve stuck open.
lPipework joints leaking or disconnected.

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-39
Possible symptoms associated with a purge valve or associated pipework failure is listed below:
lEngine may stall on return to idle if purge valve is stuck open.
lPoor idling quality if the purge valve is stuck open
lFuelling adaptions forced excessively lean if the EVAP canister is clear and the purge valve is stuck open.
lFuelling adaptions forced excessively rich if the EVAP canister is saturated and the purge valve is stuck open.
lSaturation of the EVAP canister if the purge valve is stuck closed.
To maintain driveability and effective emission control, EVAP canister purging must be closely controlled by the
engine management ECM, as a 1% concentration of fuel vapour from the EVAP canister in the air intake may shift
the air:fuel ratio by as much as 20%. The ECM must purge the fuel vapour from the EVAP canister at regular intervals
as its storage capacity is limited and an excessive build up of evaporated fuel pressure in the system could increase
the likelihood of vapour leaks. Canister purging is cycled with the fuelling adaptation as both cannot be active at the
same time. The ECM alters the PWM signal to the purge valve to control the rate of purging of the canister to maintain
the correct stoichiometric air:fuel mixture for the engine.
Fuel leak detection system (vacuum type) – NAS only
The advanced evaporative loss control system used on NAS vehicles is similar to the standard system, but also
includes a CVS valve and fuel tank pressure sensor and is capable of detecting holes in the fuel evaporative system
down to 1 mm (0.04 in.). The test is carried out in three parts. First the purge valve and the canister vent solenoid
valve closes off the storage system and the vent pressure increases due to the fuel vapour pressure level in the tank.
If the pressure level is greater than the acceptable limit, the test will abort because a false leak test response will
result. In part two of the test, the purge valve is opened and the fuel tank pressure will decrease due to the depression
from the intake manifold, evident at the purge port of the EVAP canister during purge operation. In part three of the
test, the leak measurement test is performed. The pressure response of the tests determines the level of leak, and if
this is greater than the acceptable limit on two consecutive tests, the ECM stores the fault in diagnostic memory and
the MIL light on the instrument pack is illuminated. The test is only carried out at engine idle with the vehicle stationary,
and a delay of 15 minutes after engine start is imposed before diagnosis is allowed to commence.