1995 LAND ROVER DISCOVERY electrical

19FUEL SYSTEM
2
DESCRIPTION AND OPERATION Basic ignition timing
MEMS provides the optimum ignition timing for the
relevant engine speed and load. The speed and
position of the engine is detected by the crankshaft
sensor which is bolted to, and projects through the
engine adapter plate.
The sensor incorporates an armature which runs
adjacent to a reluctor insert in the flywheel, the insert
consisting of 34 poles spaced at 10°intervals, with
two missing poles 180°apart to identify the T.D.C.
positions.
The sensor 'reads' these poles to provide a constant
up-date of engine speed and crankshaft position to
the ECM
The load signal is provided by the manifold absolute
pressure sensor mounted inside the ECM casing
which detects manifold pressure via a hose connected
to the manifold chamber. The sensor converts
pressure variations into graduated electrical signals
which can be read by the ECMIgnition timing compensation
Coolant temperature sensor
When the ECM receives a low engine temperature
signal from the coolant sensor, it provides optimum
driveability and emissions by advancing or retarding
the ignition timing.
Knock sensor
The knock sensor is a capacitive device mounted in
the cylinder block between nos. 2 and 3 cylinders
below the inlet manifold. The sensor monitors noise
and vibration in the engine and passes this
information to the ECM which is able to identify the
characteristics of the knocking and make the
necessary corrections to the ignition timing of
individual cylinders.
Idle speed control
When the throttle pedal is released and the engine is
at idle, the ECM uses the fast response of ignition
timing to assist idle speed control.
When loads are placed on, or removed from the
engine the ECM senses the change in engine speed
and in conjuction with the opening of the throttle disc
by the stepper motor, advances or retards the ignition
timing to maintain the specified idle speed. When load
is removed from the engine and the stepper motor
returns to it's original position, the ignition timing
returns to the idle setting.
NOTE: Due to the sensitivity of this system
the ignition timing will be constantly
changing at idle speed.

Mpi
5
DESCRIPTION AND OPERATION
Fuel pump
The electric fuel pump, located inside the fuel tank, is
a self-priming centrifugal 'wet' pump, the motor and
pump are filled with fuel.
The fuel pump supplies more fuel than the maximum
load requirement for the engine, so that pressure in
the fuel system can be maintained under all
conditions.
Fuel pressure regulator
The pressure regulator is a mechanical device
controlled by manifold depression and is mounted in
the fuel rail. The regulator ensures that fuel rail
pressure is maintained at a constant pressure
difference to that in the inlet manifold, as manifold
depression increases the regulated fuel pressure is
reduced in direct proportion.
When pressure exceeds the regulator setting excess
fuel is spill returned to the fuel tank swirl pot which
contains the fuel pick-up strainer.
Relay module
The relay module contains the main relay, fuel pump
relay, starter relay and oxygen sensor relay and is
mounted on the ECM mounting bracket.
The main relay is energised when the ignition is
switched on and supplies current to the ECM
The fuel pump relay is energised by the ECM for a
short period when the ignition is switched on, during
cranking and while the engine is running.
The starter relay is energised by the cranking signal
from the ignition switch.
This oxygen sensor relay is energised when the
ignition is switched on and supplies current to the
ECM
Intake air temperature sensor
The intake air temperature sensor is fitted in the side
of the inlet manifold and sends the ECM a signal
relating to air temperature. The ECM uses this signal
in its calculations on air flow.
Inertia switch
The fuel pump circuit incorporates an inertia switch
which in the event of sudden deceleration isolates the
power supply to the fuel pump. The inertia switch is
situated in the engine compartment on the bulkhead
and can, if tripped, be reset by depressing the central
plunger.
WARNING: Check the integrity of the fuel
system before the inertia switch is reset.
Diagnostic connector
A diagnostic connector is provided to enable
diagnosis to be carried out without disturbing the
system electrical connections and to allow the ECM's
ability to store certain faults to be utilised.
Oxygen sensor - Closed-loop emission control
The MEMS Mpi system operates a closed loop
emission system to ensure the most efficient level of
exhaust gas conversion.
An oxygen sensor fitted in the exhaust manifold
monitors the exhaust gases. It then supplies a small
voltage proportional to exhaust oxygen content to the
ECM As the air/fuel mixture weakens, the exhaust
oxygen content increases and so the voltage to the
ECM decreases. If the mixture becomes richer so the
oxygen content decreases and the voltage increases.
The ECM uses this signal voltage to determine the
air/fuel mixture being delivered to the engine, and
adjusts the injector duration to maintain the ratio
necessary for efficient gas conversion by the catalyst.
The oxygen sensor has an integral heating element to
ensure an efficient operating temperature is quickly
reached from cold. The electrical supply for the heater
element is controlled by the oxygen sensor relay.
Fuel temperature sensor
The fuel temperature sensor is inserted in the fuel rail
and measures fuel and fuel rail temperatures. During
engine cranking at high temperatures, the ECM
increases fuel supply, and opens the throttle disc via
the stepper motor to aid hot starting.

CRUISE CONTROL
1
FAULT DIAGNOSIS ROAD TEST
CAUTION: Do not engage cruise control
when vehicle is being used in low transfer
gear or reverse.
WARNING: The use of cruise control is not
recommended on winding, snow covered
or slippery roads or in heavy traffic
conditions where a constant speed cannot be
maintained.
1.Start engine, depress main control switch to
actuate cruise control system. Accelerate to
approximately 50 km/h, (30 mph), operate
'set/acc'switch, immediately release switch,
remove foot from accelerator pedal. Vehicle
should maintain speed at which'set/acc'switch
was operated.
2.Operate'set/acc'switch and hold at that
position, vehicle should accelerate smoothly until
switch is released. Vehicle should now maintain
new speed at which'set/acc'switch was
released.
3.Momentarily touch and release'set/acc'switch,
vehicle speed should increase 1.6 km/h (1 mph)
for each touch. Note that five touches will
increase speed 8 km/h (5 mph).
4.Apply'res/decel'switch while vehicle is in cruise
control mode, cruise control should disengage.
Slow to approximately 55 km/h, (35 mph)
operate'res/decel'switch, immediately release
switch and remove foot from accelerator, vehicle
should smoothly accelerate to previously set
speed. Increase speed using accelerator pedal,
release pedal, vehicle should return to previously
set speed.
NOTE: The cruise control system fitted to
the diesel engine is not as responsive as
that fitted to the petrol engine, due to the
characteristics of diesel engines. Therefore, at
speeds below approx. 65 km/h (40 mph), the
vehicle speed may drop when cruise is selected
and then slowly regain the 'set' speed.5.Operate brake pedal, cruise control system
should immediately disengage returning vehicle
to driver control at accelerator pedal. Operate
'res/decel'switch, vehicle should accelerate to
previously set speed without driver operation of
accelerator pedal.
6.Operate'res/decel'switch and allow vehicle to
decelerate to below 42 km/h, (26 mph). Operate
'res/decel'switch, cruise control system should
remain disengaged.
7.Operate'set/acc'switch below 40 km/h, (28
mph), cruise control system should remain
disengaged. Accelerate, using accelerator pedal
to above 45 km/h, (28 mph), operate'res/decel'
switch, and remove foot from accelerator pedal,
vehicle should smoothly adjust to previously
memorised speed.
8. Automatic vehicles- select neutral, system
should disengage.Manual vehicles- depress
clutch, system should disengage.
9.Cruise at 80 km/h (50 mph), declutch, select
neutral, remove foot from clutch. Operate
'res/decel'switch. Engine should rev to 5000
rev/min, cruise control disengages, engine
returns to idle.
10.Engage forward gear. Operate'res/decel'
switch. Remove foot from accelerator. Speed
should accelerate to previous set speed.
11.Depress main control switch in control system
should immediately disengage and erase
previously set speed from ECU memory.
See
Electrical Trouble Shooting Manual.
ELECTRICAL TESTS
Electrical functionality can be checked using
TestBook.
CABLE SETTING - TDi AUTOMATIC MODELS
1.An incorrectly adjusted kickdown cable can
prevent correct operation of the cruise control
system.
See AUTOMATIC GEARBOX,
Adjustment, kickdown cable adjustment.

19FUEL SYSTEM
6
REPAIR VACUUM PUMP - TDI
Service repair no - 19.75.06
NOTE: The vacuum pump is non
serviceable, fit a new unit if failure or
damage occurs.
Remove
1.Release turnbuckle securing wheel chock and
remove.
2.Release strap securing jack and remove.
3.Release 3 pump mounting rubbers from vehicle
body.
4.Manoeuvre pump out of box section.
5.Release multiplug cover and disconnect
multiplug from pump.
6.Disconnect vacuum hose from pump.
7.Remove pump.
Refit
8.Reverse removal procedure. Ensure all hose
and electrical connections are secure.

CRUISE CONTROL
7
REPAIR CRUISE CONTROL ECU - V8i
Service repair no - 19.75.49
Remove
1.Remove lower dash panel.
2.Disconnect ECU multi-plug.
3.Remove ECU fixing.
4.Remove ECU.
5.Reverse removal procedure. Ensuring that
electrical multi-plug is securely reconnected.
SPEED TRIP ECU - MANUAL V8i
NOTE: The neutral lock out relay
module/speed trip ECU is mounted in the
right hand side footwell. To identify
components.
See Electrical Trouble Shooting
Manual.
VEHICLE SPEED SENSOR
Service repair no - 18.30.22
For Tdi
See FUEL SYSTEM Tdi, Repair, Vehicle
Speed Sensor
For V8iSee FUEL SYSTEM MFI, Repair, Vehicle
Speed Sensor
NEUTRAL LOCK OUT RELAY
Service repair no - 19.75.28
1.Remove 3 studs securing fascia right hand side
closing panel.
2.Release and move closing panel aside.
3.Remove 2 studs securing right hand side 'A' post
lower trim casing.
4.Remove casing.
5.Locate relay (neutral coloured base) and release
base from bracket.
6.Remove relay.
NOTE: For further information.See
Electrical Trouble Shooting Manual.
Refit
7.Reverse removal procedure.

CRUISE CONTROL
9
REPAIR CRUISE CONTROL ECU - Tdi
Service repair no - 19.75.49
Remove
1.Remove 4 studs securing fascia left hand
closing panel.
2.Remove closing panel.
3.Remove nut securing ECU/relay bracket.
4.Lower bracket for access.
5.Remove bottom nut securing ECU to bracket.
6.Open glove box, align stops with cut-outs in
fascia panel and lower.
7.Move SRS harness aside.
8.Remove top nut securing ECU to bracket.
9.Disconnect ECU multiplug.
10.Remove ECU.
Refit
11.Reverse removal procedure. Ensure electrical
multiplug is securely reconnected.

Tdi
1
FAULT DIAGNOSIS ENGINE OVERHEATING
Before conducting any cooling system diagnosis:
See
Description and operation, Engine Cooling
1.Is coolant level correct?
NO - Allow engine to cool, top up level to
expansion tank seam.
YES - Continue.
2.Is drive belt tension correct?
NO -
See ENGINE, Repair, Compressor
Drive Belt
YES - Continue.
3.Is coolant in radiator frozen?
YES - Slowly thaw and drain system.
See
Adjustment, Coolant
NO - Continue.
4.Is air flow through radiator restricted or blocked?
YES - Apply air pressure from engine side of
radiator to clear obstruction.
NO - Continue.
5.Are there any external leaks, from water pump,
engine gaskets, fast idle thermostat or the heater
unit?
YES - Investigate and rectify.
See Adjustment,
Coolant
NO - Continue.
6.Are fan blades fitted correct way round, concave
side towards engine?
NO - Rectify.
YES - Continue
7.Is viscous unit operating correctly?
See
Description and operation, Viscous Fan
NO - Renew.See Repair, Viscous
Coupling, Fan Blades, Pulley and Fan
Cowl
YES - Carry out a pressure test on radiator cap
and system. Check thermostat type,
operation and correct fitting.
See Repair,
Thermostat
If pressure test leads you to suspect coolant
leakage across gaskets, go to check 10,
otherwise: Continue.8.Are the air conditioning fans operating correctly?
See Electrical Trouble Shooting Manual.
NO - Rectify.
YES - Continue.
9.Is temperature sender and gauge giving
accurate readings?
NO - Sustitute parts and compare readings.
YES - Continue.
10.Carry out cylinder pressure test to determine if
pressure is leaking into cooling system causing
over pressurising and loss of coolant.
If problem is not diagnosed, check the coolant system
for engine oil contamination and engine lubrication
system for coolant contamination.
If only the coolant system is contaminated suspect a
cylinder head gasket.
If both systems are contaminated, suspect the
radiator.
If only the lubrication system is contaminated with
coolant, suspect leakage past cylinder liner seals or
cylinder head gasket.

26COOLING SYSTEM
2
FAULT DIAGNOSIS ENGINE RUNS COLD
Before conducting any cooling system diagnosis:
See
Description and operation, Engine Cooling
1.Check operation of viscous unit.See
Description and operation, Viscous Fan
Is viscous unit operating correctly?
NO -
See Repair, Viscous Coupling, Fan
Blades, Pulley and Fan Cowl
YES - Continue.
2.Is thermostat correct type and operating?
See
Repair, Thermostat
If problem is not diagnosed: Continue.
3.Are the air conditioning fans operating
continuously?
YES -
See Electrical Trouble Shooting
Manual.
NO - Continue.
4.Is temperature sender and gauge giving
accurate readings? Substitute parts and
compare readings. If problem is not diagnosed
repeat tests, starting at 1.