1999 LAND ROVER DISCOVERY tow

ENGINE MANAGEMENT SYSTEM - V8
18-2-30 DESCRIPTION AND OPERATION
Heated Oxygen Sensors (HO2S) (C0642)
The market requirement dictates how many HO
2S are fitted to the vehicle.
l4 sensors are fitted to all NAS and EU-3 vehicles.
l2 sensors fitted to all UK, European, Australia and Japanese pre EU-3 specification vehicles.
lNo sensors fitted to ROW vehicles.
The HO
2S monitor the oxygen content of the exhaust gases. By positioning the sensors one for each bank upstream
of the catalytic converter in the exhaust pipe, the ECM can control fuelling on each bank independently of the other.
This allows greater control of the air:fuel ratio and maintains optimum catalyst efficiency. On NAS vehicles the ECM
also uses two HO
2S positioned downstream of the catalytic converters in the exhaust pipe to monitor catalytic
converter efficiency. The ECM is able to achieve this by comparing the values of the upstream HO
2S and the down
stream sensor for the same bank. These comparative values form part of the ECM OBD strategy.
The HO
2S uses zirconium contained in a galvanic cell surrounded by a gas permeable ceramic, this produces an
output voltage proportional to the ratio difference between the oxygen in the exhaust gases and to the ambient
oxygen.
The HO
2S operates at approximately 350 °C (662 °F). To achieve this temperature the HO2S incorporate a heating
element which is controlled by a PWM signal from the ECM. The elements are activated immediately after engine
starts and also under low engine load conditions when the exhaust gas temperature is insufficient to maintain the
required HO
2S temperature. If the heater fails, the ECM will not allow closed loop fuelling to be implemented until the
sensor has achieved the required temperature.
This value equates to an HO
2S output of 450 to 500 mV. A richer mixture can be shown as λ = 0.97, this pushes the
HO
2S output voltage towards 1000 mV. A leaner mixture can be shown as λ = 1.10, this pushes the HO2S output
voltage towards 100 mV.
From cold start, the ECM runs an open loop fuelling strategy. The ECM keeps this strategy in place until the HO
2S is
at a working temperature of 350 °C (662 °F). At this point the ECM starts to receive HO
2S information and it can then
switch into closed loop fuelling as part of its adaptive strategy. The maximum working temperature of the tip of the
HO
2S is 930 °C (1706 °F), temperatures above this will damage the sensor.
HO
2S age with use, this increases their response time to switch from rich to lean and from lean to rich. This can lead
to increased exhaust emissions over a period of time. The switching time of the upstream sensors are monitored by
the ECM. If a pre-determined threshold is exceeded, a failure is detected and the MIL illuminated.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Exhaust Emission Control System.
Input/Output
The upstream and downstream HO
2S are colour coded to prevent incorrect fitting. The tips of the upstream sensors
are physically different to the tips of the downstream sensors.
The HO
2S are colour coded as follows:
lUpstream sensors (both banks) - orange.
lDownstream sensors (both banks) - grey.
The four HO
2S have a direct battery supply to the heater via fuse 2 located in the engine compartment fuse box.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-31
The heater is driven by the ECM providing an earth path for the circuit as follows:
lUpstream LH bank via pin 19 of connector C0635 of the ECM.
lUpstream RH bank via pin 13 of connector C0635 of the ECM.
lDownstream LH bank via pin 7 of connector C0635 of the ECM.
lDownstream RH bank via pin 1 of connector C0635 of the ECM.
The HO
2S output signal is measured by the ECM as follows:
lUpstream LH bank via pin 15 of connector C0635 of the ECM.
lUpstream RH bank via pin 16 of connector C0635 of the ECM.
lDownstream LH bank via pin 17 of connector C0635 of the ECM.
lDownstream RH bank via pin 14 of connector C0635 of the ECM.
The HO
2S earth path for the signal is supplied by the ECM as follows:
lUpstream LH bank via pin 9 of connector C0635 of the ECM.
lUpstream RH bank via pin 10 of connector C0635 of the ECM.
lDownstream LH bank via pin 11 of connector C0635 of the ECM.
lDownstream RH bank via pin 8 of connector C0635 of the ECM.
The HO
2S voltage is difficult to measure using a multimeter, the output can be monitored using TestBook. A rich
mixture would read 500 to 1000 mV, a weak mixture would read 100 mV to 500 mV, the reading should switch from
rich to weak. The open loop default voltage is 450 mV, this is used by the ECM to set the air/ fuel ratio until the tip of
the HO
2S reaches operating temperature.
The HO
2S can fail the following ways or supply incorrect signal:
lSensor open circuit.
lShort circuit to vehicle supply.
lShort circuit to vehicle earth.
lSensor disconnected.
lStoichiometric ratio outside the correct operating band.
lContamination from leaded fuel.
lAir leak into the exhaust system.
lWiring loom damage.
lSensors fitted incorrectly or cross wired.
In the event of a HO
2S signal failure any of the following symptoms may be observed:
lDefault to open loop fuelling on defective bank.
lIf the sensors are crossed over (LH bank to RH bank), the engine will run normally after initial start up, but
performance will become progressively worse as the sensors go towards maximum rich for one bank of cylinders
and maximum lean for the other. The ECM will eventually default into open loop fuelling.
lHigh CO reading.
lExcess emissions.
lStrong hydrogen sulphide (H
2S) smell until the ECM defaults to open loop fuelling. .
lMIL illuminated (NAS market only).
A number of diagnostic tests are performed by the ECM with regards to the HO
2sensors:
lHO
2 sensor and system diagnostics
lHO
2 sensor heater diagnostics
lHO
2 sensor switching period (ageing) diagnostics
lRear HO
2 sensor adaption diagnostic (NAS only)
lCatalyst monitoring diagnostic
For further details of the heated oxygen sensors and exhaust emission control, refer to the V8 Emission Control
section of this manual.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Exhaust Emission Control System.

MANIFOLDS AND EXHAUST SYSTEMS - V8
30-2-6 DESCRIPTION AND OPERATION
Exhaust manifolds
Two handed, cast iron exhaust manifolds are used on the V8 engine. Each manifold has four ports which merge into
one flanged outlet positioned centrally on the manifold.
Each manifold is attached to its cylinder head with eight Torx bolts. Each bolt is fitted with a 'cotton reel' shaped spacer
which allows for a longer bolt resulting in increased torque loading on each bolt. Two laminated metal gaskets seal
each manifold to its cylinder head. The flanged outlet on each manifold provides the attachment for the front pipe of
the exhaust system.
Exhaust system
The exhaust system comprises a front pipe assembly with two front pipes each incorporating a catalytic converter, an
intermediate pipe incorporating a silencer and a tail pipe assembly which also has a silencer. The exhaust system is
constructed mainly of 63 mm (2.48 in) diameter extruded pipe with a 1.5 mm (0.06 in) wall thickness. All pipes are
aluminized to resist corrosion and the silencers are fabricated from stainless steel sheet.
Front pipe assembly
The front pipe assembly is of welded and fabricated construction. A front pipe from each exhaust manifold merges
into one flanged connection. Two captive studs on the flange provide attachment to the intermediate pipe with
locknuts. Each front pipe has a welded flange which is attached to each manifold and secured with three studs and
flanged nuts and sealed with a metal laminated gasket. The gasket comprises a heat resistant fibre between two thin
metallic layers to enhance the sealing properties of the gasket.
A catalytic converter is located in each front pipe. The catalytic converters are different shapes to allow clearance
between the body and transmission. Both catalytic converters are of similar internal construction.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Emission Control Systems.
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.
From the catalytic converters, the front pipes merge into one pipe which terminates at a flanged joint. The flange
connects with the intermediate pipe, sealed with an olive and secured with studs and locknuts.
Intermediate pipe and silencer
The intermediate pipe is of welded and fabricated tubular construction. It connects at its forward end with a flange on
the front pipe assembly and is secured with locknuts to captive studs in the front pipe assembly flange. The rear
section of the intermediate pipe connects to the tail pipe assembly via a flanged joint, sealed with a metal gasket and
secured with locknuts and studs.
The forward and rear sections are joined by a silencer. The silencer is fabricated from stainless steel sheet to form
the body of the silencer. An end plate closes each end of the silencer and is attached to the body with seam joints.
Perforated baffle tubes inside the silencer are connected to the inlet and outlet pipes on each end plate. Internal baffle
plates support the baffle tubes and together with a stainless steel fibre absorb combustion noise as the exhaust gases
pass through the silencer.
The intermediate pipe is attached by two brackets, positioned at each end of the silencer, and mounting rubbers to
the chassis. The mounting rubbers allow ease of alignment and vibration absorption. The two mounting rubbers are
fitted with removable heat deflectors to prevent heat from the silencer damaging the material.
Tail pipe assembly
The tail pipe is of welded and fabricated construction. It connects to the intermediate pipe with a flanged joint secured
with studs and locknuts and sealed with a metal gasket. The pipe is shaped to locate above the rear axle allowing
clearance for axle articulation. The pipe is also curved to clear the left hand side of the fuel tank which has a reflective
shield to protect the tank from heat generated from the pipe.
A fabricated silencer is located at the rear of the tail pipe. The silencer is circular in section and is constructed from
stainless steel sheet. A baffle tube is located inside the silencer and the space around the baffle tube is packed with
a stainless steel fibre. The holes in the baffle tube allow the packing to further reduce combustion noise from the
engine. The tail pipe from the silencer is curved downwards at the rear of the vehicle and directs exhaust gases
towards the ground. The curved pipe allows the exhaust gases to be dissipated by the airflow under the vehicle and
prevents gases being drawn behind the vehicle.
The tail pipe is attached by a bracket, positioned forward of the silencer, and a mounting rubber to the chassis. The
mounting rubber allows ease of alignment and vibration absorption.

CLUTCH - V8
DESCRIPTION AND OPERATION 33-2-9
Operation
Hydraulic operation
Refer to illustration.

+ CLUTCH - V8, DESCRIPTION AND OPERATION, Hydraulic operation.
When the clutch pedal is depressed, the master cylinder piston is pushed into the master cylinder. The movement of
the piston pressurises the fluid in the master cylinder, forcing the pressurised fluid into the hydraulic feed pipe to the
slave cylinder. The hydraulic pressure is felt at the slave cylinder piston which moves under the hydraulic force
applied, pushing the clutch release lever via the piston rod.
When the clutch pedal is released, the force applied to the release lever by the fingers of the diaphragm, moves the
release lever, which pushes the slave cylinder piston into the cylinder. The displaced hydraulic fluid is pushed up the
hydraulic feed pipe and returned to the master cylinder.
Mechanism operation
When the clutch pedal is depressed, hydraulic pressure extends the piston and rod in the slave cylinder. The
extension of the piston pushes the rod against the outer end of the release lever which pivots around the ball spigot.
The inner end of the release lever pivots towards the engine applying pressure to the release bearing. The release
bearing slides along the release bearing sleeve and pushes on the fingers of the diaphragm. The diaphragm pivots
about the fulcrum rings in the cover. As the diaphragm is deflected, it removes pressure from the pressure plate. The
pressure plate moves away from the drive plate assisted by the three leaf springs and retractor clips.
The removal of force from the pressure plate on the drive plate reduces the friction between the flywheel, drive plate
and pressure plate. The drive plate slips between the flywheel and the pressure plate preventing rotary movement
being transferred from the flywheel and pressure plate to the primary driveshaft.
When the clutch pedal is released, hydraulic force is removed from the piston in the slave cylinder. This allows the
fingers of the diaphragm to push the release bearing along the release bearing sleeve. The movement of the release
bearing moves the release lever which pivots on the ball spigot, pushing the piston and rod back into the slave
cylinder.
The removal of pressure from the release bearing on the diaphragm, causes the diaphragm to pivot around the
fulcrum rings in the cover. The force applied to the pressure plate from the diaphragm overcomes the force of the leaf
springs and the pressure plate moves towards the drive plate and flywheel.
The pressure plate applies pressure to the drive plate which is pushed against the flywheel. As the clutch pedal is
progressively released, the friction between the drive plate, flywheel and pressure plate increases. The increase in
friction transfers the rotary movement of the flywheel and pressure plate to the drive plate which in turn starts to rotate
the primary driveshaft. When the clutch pedal is released fully, the force applied by the diaphragm to the pressure
plate forces the drive plate onto the flywheel with no slippage.

MANUAL GEARBOX - R380
37-24 REPAIRS
Cooler - oil - gearbox - V8
$% 37.24.02
Remove
1. If fitted: Remove engine oil cooler.

+ ENGINE - V8, REPAIRS, Cooler -
engine oil.
2.Position absorbent cloth under each gearbox
oil cooler hose connection to collect spillage.
3.Push against coupling release rings and
disconnect both hoses from oil cooler.
CAUTION: Always fit plugs to open
connections to prevent contamination.
4.Remove screw securing oil cooler to radiator.
5.Release oil cooler from its location on radiator. 6.Move radiator towards engine sufficiently only
to release gearbox oil cooler from radiator.
7.Remove gearbox oil cooler.
CAUTION: Always fit plugs to open
connections to prevent contamination.
Refit
1.Fit gearbox oil cooler to radiator, engage in
location and secure with screw.
2.Ensure connections are clean and secure
hoses to cooler.
3. If fitted: Fit engine oil cooler.

+ ENGINE - V8, REPAIRS, Cooler -
engine oil.
4.Top up gearbox oil.

+ MAINTENANCE, PROCEDURES,
Manual gearbox.

MANUAL GEARBOX - R380
37-40 OVERHAUL
12.Fit new output shaft oil seal using tool LRT-37-
014.
13.Fit oil pick-up pipe with the off-set uppermost.
14.Lubricate oil pump recess with gearbox oil.
15.Lubricate a new 'O' ring with gearbox oil and fit
to oil pump.
16.Locate oil pump in extension housing with word
'TOP' towards top of housing.
17.Align oil pump fixing screw holes and tap pump
lightly around edges until it is fully in recess.
Do not attempt to pull pump into recess
using fixing screws.
18.Fit Torx screws and tighten to 6 Nm (4.5 lbf.ft).
19.Remove 2 slave bolts securing centre plate to
gearbox casing.
20.Apply sealant, Part No. STC 4404 to gearbox
casing face.
21.Position extension housing, align oil pump drive
with layshaft.
22.Clean extension housing bolt threads.
23.Apply sealant, Part No. STC 50552 to threads
of extension housing bolts, fit bolts ensuring 2
longest bolts are in their original positions and
tighten by diagonal selection to 25 Nm (18
lbf.ft).
24.Using new 'O' ring, fit interlock spool retainer
and tighten bolt to 8 Nm (6 lbf.ft). 25.Using tool LRT-37-015 and LRT-37-021, fit oil
seal collar.
26.Clean gear selector selector housing and
mating face.
27.Apply sealant, Part No. STC 4404 to gear
selector housing face.
28.Position gear selector housing and tighten
bolts to 25 Nm (18 lbf.ft).

MANUAL GEARBOX - R380
OVERHAUL 37-41
Pump - gearbox oil
$% 37.12.47
Disassembly
1.Remove gearbox extension.

+ MANUAL GEARBOX - R380,
OVERHAUL, Extension - gearbox rear.
2.Remove 3 Torx screws, remove oil pump and
discard 'O' ring.
Reassembly
1.Clean oil pump recess in extension housing,
ensure screw holes are clean and dry.
2.Lubricate oil pump recess in housing with
gearbox oil.
3.Lubricate a new 'O' ring with gearbox oil and fit
to oil pump.
4.Locate oil pump in extension housing with word
'TOP' towards top of housing.
5.Align fixing screw holes and tap pump lightly
around edges until pump is fully in housing. Do
not pull pump into housing by tightening
screws.
6.Fit Torx screws and tighten to 6 Nm (4.5 lbf.ft).
7.Fit gearbox extension.

+ MANUAL GEARBOX - R380,
OVERHAUL, Extension - gearbox rear.
Filter - gearbox oil
$% 37.12.38
Disassembly
1.Remove gearbox extension.

+ MANUAL GEARBOX - R380,
OVERHAUL, Extension - gearbox rear.
2.Remove oil filter from gearbox.
Reassembly
1.Clean filter recess in gearbox.
2.Fit filter.
3.Fit gearbox extension.

+ MANUAL GEARBOX - R380,
OVERHAUL, Extension - gearbox rear.

MANUAL GEARBOX - R380
OVERHAUL 37-45
6.Remove split collar and 5th gear from layshaft. Reassembly
1.Clean gear and layshaft.
2.Position 5th gear and split collar to layshaft
ensuring that bevelled side of collar is towards
5th gear.
3.Position split collars and retaining ring securing
5th gear to output shaft.
4.Position tool LRT-37-023 to hold 5th gear and
tighten new stake nut to 220 Nm (162 lbf.ft) and
stake nut.
5.Apply a small amount of heat and fit support
bearing track to layshaft.
6.Fit gearbox extension.

+ MANUAL GEARBOX - R380,
OVERHAUL, Extension - gearbox rear.