1999 LAND ROVER DISCOVERY overheating

MAINTENANCE
10-10 PROCEDURES
Spark plugs - V8 engine
Replace
Take great care when fitting spark plugs not
to cross-thread plug, otherwise costly
damage to cylinder head will result. It is
essential that correct grade of spark plugs
are fitted. Incorrect grade of spark plugs
may lead to piston overheating and engine
failure. Use only approved spark plugs, use
of unapproved spark plugs may cause the
misfire detection system to malfunction.
1.Disconnect battery earth lead.
2.Noting their fitted position, disconnect ht leads
from spark plugs.
3.Remove 8 spark plugs.
4.Ensure that gap of new spark plugs is 1.0 ±
0.05 mm (0.040 ± 0.002 in).
Do not attempt to clean or adjust gaps. If a
spark plug problem exists, try substituting
defective spark plug(s) with new one(s).
CAUTION: Do not attempt to clean or adjust
spark plug gaps. If a spark plug problem
exists, try substituting the defective spark
plug with a new one.
5.Fit spark plugs and tighten to 20 Nm (15 lbf.ft).
6.Connect ht leads to spark plugs.
7.Connect battery earth lead.
Air cleaner - V8 engine
Replace
1.Replace air cleaner element.

+ ENGINE MANAGEMENT SYSTEM -
V8, REPAIRS, Element - air filter.
Clean
1.Clean the drain hole in filter casing.
Air cleaner and dump valve - diesel
engine
Replace/clean
1.Replace air cleaner element.

+ ENGINE MANAGEMENT SYSTEM -
Td5, REPAIRS, Element - air filter.
2.Remove all dirt from dump valve.

ENGINE - V8
12-2-68 OVERHAUL
10.Position body of tool LRT-12-013 in vice.
11.Screw large nut back until flush with end of
centre screw.
12.Push centre screw forward until nut contacts
thrust race.
13.Position remover/replacer LRT-12-126/2 in
LRT-12-013 with its long spigot inside bore of
hexagon body.
14.Locate piston and connecting rod assembly on
centre screw and up to remover/replacer
adapter tool LRT-12-126/2.
CAUTION: Ensure that prongs of remover/
replacer adapter LRT-12-162/2 remain in
contact with piston and do not contact
gudgeon pin.
15.Fit remover/replacer bush LRT-12-126/1 on
centre screw with flanged end facing away from
gudgeon pin.
CAUTION: Ensure that remover/replacer
bush LRT-12-126/1 is correctly located in
gudgeon pin bore of piston.
16.Screw stop nut onto centre screw.
17.Lock the stop nut securely with the lock screw.
18.Push connecting rod to locate end of gudgeon
pin in remover/replacer adapter LRT-12-126/2.
19.Ensure remover/replacer bush LRT-12-126/1
is located in gudgeon pin bore of piston.
20.Screw large nut up to tool LRT-12-013.
21.Hold lock screw and turn large nut until
gudgeon pin is withdrawn from piston.
CAUTION: Ensure that prongs of tool LRT-
12–126/2 remain in contact with piston and
do not contact the gudgeon pin.
22.Dismantle tool LRT-12-013 and remove piston,
connecting rod and gudgeon pin. Inspect
1.Clean carbon from piston. Inspect piston for
distortion, cracks and burning.
2.Remove piston rings from piston.
3.Measure and record piston diameter at 90° to
gudgeon pin axis and 10 mm (0.4 in) from
bottom of the skirt. The piston must be 0.015 to
0.045 mm (0.001 to 0.002 in) smaller than the
cylinder bore.
4.Check gudgeon pin bore in piston for signs of
wear and overheating.
5.Pistons fitted on production are graded 'A' or
'B', the grade letter is stamped on the piston
crown.
lPiston diameter: Grade 'A' = 93.970 to
93.985 mm (3.6996 to 3.7002 in).
lPiston diameter: Grade 'B' = 93.986 to 94.00
mm (3.7002 to 3.7007 in).
6.Worn cylinders fitted with grade 'A' pistons may
be honed to accept the grade 'B' piston
provided that specified cylinder bore and
ovality limits are maintained. Grade 'B'
pistons are supplied as service
replacements. Do not attempt to de-glaze
cylinder bores.
CAUTION: Ensure replacement pistons are
correct for the compression ratio of the
engine. The compression ratio will be found
on the cylinder block adjacent to the engine
serial number.
7.Check gudgeon pins for signs of wear and
overheating.
8.Check clearance of gudgeon pin in piston.
l Gudgeon pin to piston clearance = 0.006 to
0.015 mm (0.0002 to 0.0006 in).

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-11
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.
lWhen λ = 1, the air to fuel ratio corresponds to the theoretical optimum of 14.7:1 and is the desired condition for
minimising emissions.
lWhen 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.
lWhen 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.
Changes in the oxygen content has subsequent effects on the levels of exhaust emissions experienced. The levels
of hydrocarbons and carbon monoxide produced around the stoichiometric ideal control range are minimised, but
peak emission of oxides of nitrogen are experienced around the same range.

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-43
Secondary Air Injection System
Operation
When the engine is started, the engine control module checks the engine coolant temperature and if it is below 55°
C, the ECM grounds the electrical connection to the coil of the secondary air injection (SAI) pump relay.
A 12V battery supply is fed to the inertia switch via fuse 13 in the engine compartment fusebox. When the inertia
switch contacts are closed, the feed passes through the switch and is connected to the coil of the Main relay. An earth
connection from the Main relay coil is connected to the ECM. When the ECM completes the earth path, the coil
energises and closes the contacts of the Main relay.
The Main and Secondary Air Injection (SAI) pump relays are located in the engine compartment fusebox. When the
contacts of the Main relay are closed, a 12V battery supply is fed to the coil of the SAI pump relay. An earth connection
from the coil of the SAI pump relay is connected to the ECM. When the ECM completes the earth path, the coil
energises and closes the contacts of the SAI pump relay to supply 12V to the SAI pump via fusible link 2 in the engine
compartment fusebox. The SAI pump starts to operate, and will continue to do so until the ECM switches off the earth
connection to the coil of the SAI pump relay.
The SAI pump remains operational for a period determined by the ECM and depends on the starting temperature of
the engine, or for a maximum operation period determined by the ECM if the target engine coolant temperature has
not been reached in the usual time.
When the contacts of the main relay are closed, a 12V battery supply is fed to the SAI solenoid valve via Fuse 2 in
the engine compartment fusebox.
The ECM grounds the electrical connection to the SAI vacuum solenoid valve at the same time as it switches on the
SAI pump motor. When the SAI vacuum solenoid valve is energised, a vacuum is provided to the operation control
ports on both of the vacuum operated SAI control valves at the exhaust manifolds. The control vacuum is sourced
from the intake manifold depression and routed to the SAI control valves via a vacuum reservoir and the SAI vacuum
solenoid valve.
The vacuum reservoir is included in the vacuum supply circuit to prevent vacuum fluctuations caused by changes in
the intake manifold depression affecting the operation of the SAI control valves.
When a vacuum is applied to the control ports of the SAI control valves, the valves open to allow pressurised air from
the SAI pump to pass through to the exhaust ports in the cylinder heads for combustion.
When the ECM has determined that the SAI pump has operated for the desired duration, it switches off the earth paths
to the SAI pump relay and the SAI vacuum solenoid valve. With the SAI vacuum solenoid valve de-energised, the
valve closes, cutting off the vacuum supply to the SAI control valves. The SAI control valves close immediately and
completely to prevent any further pressurised air from the SAI pump entering the exhaust manifolds.
The engine coolant temperature sensor incurs a time lag in respect of detecting a change in temperature and the SAI
pump automatically enters a 'soak period' between operations to prevent the SAI pump overheating. The ECM also
compares the switch off and start up temperatures, to determine whether it is necessary to operate the SAI pump.
This prevents the pump running repeatedly and overheating on repeat starts.
Other factors which may prevent or stop SAI pump operation include the prevailing engine speed / load conditions.

ENGINE MANAGEMENT SYSTEM - V8
18-2-40 DESCRIPTION AND OPERATION
Ignition coils
Two double ended ignition coils are located at the rear of the engine, below the inlet plenum camber mounted on a
bracket. The ignition system operates on the wasted spark principle. When the ECM triggers an ignition coil to spark,
current from the coil travels to one spark plug jumping the gap at the spark plug electrodes igniting the mixture in the
cylinder. Current continues to travel along the earth path (via the cylinder head) to the spark plug negative electrode
at the cylinder that is on the exhaust stroke. The current jumps across the spark plug electrodes and back to the coil
completing the circuit. Since it has sparked simultaneously in a cylinder that is on the exhaust stroke it has not done
any work, therefore it is wasted.
The coils are paired in the following cylinder order:
l1 and 6.
l8 and 5.
l4 and 7.
l3 and 2.
The ECM calculates the dwell timing from battery voltage, and engine speed to ensure constant secondary energy.
This ensures sufficient spark energy is always available without excessive primary current flow and thus avoiding
overheating or damage to the coils. Individual cylinder spark timing is calculated from the following signals:
lEngine speed.
lEngine load.
lEngine temperature.
lKnock control.
lAutomatic gearbox shift control.
lIdle speed control.
During engine warm up ignition timing should be an expected value of 12° BTDC.
TestBook can not directly carry out diagnostics on the high-tension side of the ignition system. Ignition related faults
are monitored indirectly by the misfire detection system.

COOLING SYSTEM - V8
DESCRIPTION AND OPERATION 26-2-7
Inlet manifold - Cooling connections
Coolant leaves the cylinder block via an outlet pipe attached to the front of the air intake manifold. The pipe is
connected to the thermostat housing and the radiator by a branch hose off the radiator top hose.
Hot coolant from the engine is also directed from the inlet manifold via pipes and hoses into the heater matrix. Coolant
is circulated through the heater matrix at all times when the engine is running.
A further tapping from the inlet manifold supplies coolant to the throttle housing via a hose. The coolant circulates
through a plate attached to the bottom of the housing and is returned through a plastic bleed pipe to an expansion
tank. The hot coolant heats the air intake of the throttle housing preventing ice from forming.
An Engine Coolant Temperature (ECT) sensor is fitted in the inlet manifold adjacent to the manifold outlet pipe. The
sensor monitors coolant temperature emerging from the engine and sends signals to the ECM for engine
management and temperature gauge operation.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
Expansion tank
The expansion tank is located in the engine compartment. The tank is made from moulded plastic and attached to
brackets on the right hand inner wing. A maximum coolant when cold level is moulded onto the tank.
Excess coolant created by heat expansion is returned to the expansion tank from the radiator bleed pipe at the top of
the radiator. An outlet pipe is connected into the pump feed hose and replaces the coolant displaced by heat
expansion into the system when the engine is cool.
The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve which opens to allow
excessive pressure and coolant to vent through the overflow pipe. The relief valve opens at a pressure of 1.4 bar (20
lbf.in
2) and above.
Heater matrix
The heater matrix is fitted in the heater assembly inside the passenger compartment. Two pipes pass through the
bulkhead into the engine compartment and provide coolant flow to and from the matrix. The pipes from the bulkhead
are connected to the matrix, sealed with 'O' rings and clamped with circular rings.
The matrix is constructed from aluminium with two end tanks interconnected with tubes. Aluminium fins are located
between the tubes and conduct heat away from the hot coolant flowing through the tubes. Air from the heater
assembly is warmed as it passes through the matrix fins. The warm air is then distributed into the passenger
compartment as required.

+ HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description.When the engine is
running, coolant from the engine is constantly circulated through the heater matrix.
Radiator
The 45 row radiator is located at the front of the vehicle. The cross-flow type radiator is manufactured from aluminium
with moulded plastic end tanks interconnected with tubes. Aluminium fins are located between the tubes and conduct
heat from the hot coolant flowing through the tubes, reducing the cooling temperature as it flows through the radiator.
Air intake from the front of the vehicle when moving carries heat away from the fins. When the vehicle is stationary,
the viscous fan draws air through the radiator fins to prevent the engine from overheating.
Two connections at the top of the radiator provide for the attachment of the top hose and bleed pipe. A connection at
the bottom of the radiator allows for the attachment of the bottom hose to the thermostat housing.
Two smaller radiators are located in front of the cooling radiator. The lower radiator provides cooling of the gearbox
oil and the upper radiator provides cooling for the engine oil.

+ MANUAL GEARBOX - R380, DESCRIPTION AND OPERATION, Description.

+ AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.

+ ENGINE - V8, DESCRIPTION AND OPERATION, Description.
Pipes and hoses
The coolant circuit comprises flexible hoses and metal formed pipes which direct coolant into and out of the engine,
radiator and heater matrix. Plastic pipes are used for the bleed and overflow pipes to the expansion tank.
A bleed screw is installed in the radiator top hose and is used to bleed air during system filling. A drain plug is fitted
to each cylinder bank in the cylinder block. These are used to drain the block of coolant.

BRAKES
70-22 DESCRIPTION AND OPERATION
Minimum target speed
The minimum target speed depends on which gear is engaged. Reduced minimum target speeds are employed for
some gears if rough terrain or sharp bends are encountered while already travelling at the normal minimum target
speed. If loss of traction makes it impossible to maintain the minimum target speed, the SLABS ECU temporarily
increases the minimum target speed to maintain stability, then restores the normal minimum target speed when
traction improves.
HDC minimum target speeds
Fade out
To provide a safe transition from active braking to brakes off, the SLABS ECU invokes a fade out strategy if it detects
any of the following during active braking:
lA system fault.
lThe conditions for HDC are no longer being met.
lPossible brake overheat.
The fade out strategy increases the target speed at a low constant acceleration rate, independent of actual throttle
position. This results in the braking effort being gradually reduced and then discontinued. The SLABS ECU operates
warning indications during fade out that are dependent on the cause.
Fade out warning indications
Clutch disengagement/neutral selection
During active braking, if the SLABS ECU detects the clutch is disengaged or neutral is selected, it flashes the HDC
information warning lamp and sounds the audible warning continuously to indicate that conditions for HDC are no
longer being met. Initially, the SLABS ECU also fixes the target speed to the applicable minimum target speed, but if
the condition continues for approximately 60 seconds the SLABS ECU invokes fade out.
Brake overheat prevention
To prevent the brakes overheating, the SLABS ECU monitors the amount of active braking employed and, from this,
estimates brake temperature. If the SLABS ECU estimates the brake temperature has exceeded a preset limit, it
flashes the HDC fault warning lamp and sounds the audible warning continuously, to indicate that HDC should be
deselected to allow the brakes to cool. If active braking continues and the SLABS ECU estimates that brake
temperature has increased to an unacceptable level, fade out is employed and HDC is disabled. After fade out, the
audible warning is discontinued but the HDC fault warning lamp continues to flash, while HDC is selected, until the
SLABS ECU estimates brake temperature to be at an acceptable level. This calculation continues even if the ignition
is turned off, so turning the ignition off and back on will not reduce the disabled time. When the SLABS ECU estimates
the brake temperature to be acceptable, it extinguishes the HDC fault warning lamp and illuminates the HDC
information warning lamp to indicate that HDC is re-enabled. The disabled time is dependent on vehicle speed; typical
times at constant vehicle speeds are as follows:
Gear Speed, mph (km/h)
Manual gearbox Automatic gearbox
Normal Reduced Normal Reduced
1 4.4 (7.0) 4.4 (7.0) 4.4 (7.0) 4.4 (7.0)
2 5.2 (8.3) 4.4 (7.0) 4.4 (7.0) 4.4 (7.0)
3 6.0 (9.6) 4.4 (7.0) 7.5 (12.0) 6.0 (9.6)
4 7.5 (12.0) 6.0 (9.6) 7.5 (12.0) 6.0 (9.6)
5 8.8 (14.0) 7.0 (11.2) - -
Reverse 3.5 (5.6) 3.5 (5.6) 3.5 (5.6) 3.5 (5.6)
Neutral or clutch
disengaged8.8 (14.0) Last off road speed 4.4 (7.0) 4.4 (7.0)
Cause Warning indication
HDC fault warning lamp HDC information
warning lampAudible warning
Fault detected On Flashes Continuous
HDC conditions not met Off Flashes Continuous
Brake overheat prevention Flashes Off Continuous