1995 LAND ROVER DISCOVERY sensor

SFI
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DESCRIPTION AND OPERATION ENGINE MANAGEMENT SYSTEM
Description
The engine management system (EMS) maintains
optimum engine performance over the entire
operating range. The correct amount of fuel is
metered into each cylinder inlet tract and the ignition
timing is adjusted at each spark plug.
The system is controlled by the ENGINE CONTROL
MODULE (ECM) which receives data from sensors
located on and around the engine. From this
information it provides the correct fuel requirements
and ignition timing at all engine loads and speeds.
The fuel injection system uses a hot wire Mass Air
Flow Sensor to calculate the amount of air flowing into
the engine.
The ignition system does not use a distributor. It is a
direct ignition system (DIS), using four double ended
coils. The circuit to each coil is completed by
switching inside the ECM.
The on board diagnostic system detects any faults
which may occur within the EMS. Fault diagnosis
includes failure of all EMS sensors and actuators,
emissions related items, fuel supply and exhaust
systems.
The system incorporates certain default strategies to
enable the vehicle to be driven in case of sensor
failure. This may mean that a fault is not detected by
the driver. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
A further feature of the system is 'robust
immobilisation'.Crankshaft position sensor (CKP Sensor)
The crankshaft position sensor is the most important
sensor on the engine. It is located in the left hand side
of the flywheel housing and uses a different thickness
of spacer for manual and automatic gearboxes. The
signal it produces informs the ECM:
- the engine is turning
- how fast the engine is turning
- which stage the engine is at in the cycle.
As there is no default strategy, failure of the
crankshaft sensor will result in the engine failing to
start. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
Camshaft position sensor (CMP Sensor)
The camshaft position sensor is located in the engine
front cover. It produces one pulse every two
revolutions. The signal is used in two areas, injector
timing corrections for fully sequential fuelling and
active knock control.
If the camshaft sensor fails, default operation is to
continue normal ignition timing. The fuel injectors will
be actuated sequentially, timing the injection with
respect to top dead centre. Injection will either be
correct or one revolution out of synchronisation. The
fault is not easily detected by the driver. The fault is
indicated by illumination of the malfunction indicator
light (MIL) on North American specification vehicles.
Mass air flow sensor (MAF Sensor)
The 'hot wire' type mass air flow sensor is mounted
rigidly to the air filter and connected by flexible hose to
the plenum chamber inlet. The sensing element of the
MAF Sensor is a hot wire anenometer consisting of
two wires, a sensing wire which is heated and a
compensating wire which is not heated. Air flows
across the wires cooling the heated one, changing its
resistance. The ECM measures this change in
resistance and calculates the amount of air flowing
into the engine.
As there is no default strategy, failure will result in the
engine starting, and dying when it reaches 550
rev/min, when the ECM detects no MAF Sensor
signal. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.

19FUEL SYSTEM
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DESCRIPTION AND OPERATION REV: 09/95 ENGINE MANAGEMENT SYSTEM COMPONENT
LOCATION - PRE ADVANCED EVAPS
1. Engine control module
2. Ignition coils
3. Fuel pressure regulator
4. Mass air flow sensor
5. Relay module
- Main relay
- Fuel pump relay
6. Engine coolant temperature sensor
7. Camshaft position sensor
8. Throttle position sensor

SFI
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DESCRIPTION AND OPERATION
1. EVAP purge valve
2. Inertia switch
3. Engine fuel temperature sensor
4. Crankshaft position sensor
5. Oxygen sensor (4 off)
6. Injectors
7. Idle air control
8. Knock sensors (2 off)
9. Intake air temperature sensor

19FUEL SYSTEM
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DESCRIPTION AND OPERATION Throttle position sensor (TP Sensor)
The throttle position sensor is mounted on the plenum
chamber and connected directly to the throttle shaft.
The sensor is a variable resistor, the signal from
which (0 - 5V) informs the ECM of the actual position
of the throttle disc. As there is no default strategy,
failure of the sensor will result in poor idle and lack of
throttle response. If failure occurs in the closed
position the engine will only reach 1750 rev/min when
the ECM will initiate overrun fuel cut off. The fault is
indicated by illumination of the malfunction indicator
light (MIL) on North American specification vehicles.
Engine coolant temperature sensor (ECT Sensor)
This sensor consists of a temperature dependant
resistive metal strip. The resistance of the strip varies
considerably with coolant temperature, i.e. from 28K
ohms at - 30°C to 90 ohms at 130°C, and 300 Ohms
at 85°C. The ECT Sensor signal is vital to engine
running, as the correct fuelling is dependant upon
engine temperature i.e. richer mixture at low
temperatures. If the sensor is disconnected or failure
occurs a default value will be supplied to the system.
The initial default value selected will be based on the
value of the air intake temperature. This will increase
to a nominal warmed up value over an individual time,
programmed for each default value. The fault may not
be evident to the driver, there may be a hot restart
problem. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.Intake air temperature sensor (IAT Sensor)
This is another resistive sensor, located in the body of
the air cleaner. The resistance varies with changes in
air temperature. The signal from the IAT Sensor is
used to retard the ignition timing if the air temperature
rises above 55°C. If the sensor is disconnected or
failure occurs a default value will be supplied to the
system. The default value selected will represent
normal operating conditions. The fault may not be
evident to the driver, there may be slight power loss in
high ambient temperatures. The fault is indicated by
illumination of the malfunction indicator light (MIL) on
North American specification vehicles.

SFI
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DESCRIPTION AND OPERATION REV: 09/95 Engine fuel temperature sensor (EFT Sensor)
This is another resistive sensor. Located on the fuel
rail it measures temperature of the rail rather than the
fuel. The resistance varies with changes in
temperature. The signal is used to increase the
injection pulse time when undergoing hot restarts.
When the fuel is hot, vapourisation occurs in the rail
and bubbles can occur in the injectors. Increasing the
pulse time flushes the bubbles away, and cools the
fuel rail with fuel from the tank. The fault may not be
evident to the driver, there may be a hot restart
problem. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
Knock sensors
The knock sensor produces an output voltage in
proportion to mechanical vibration caused by the
engine. A sensor is located in each cylinder bank
between 2/4 and 3/5 cylinders. The ECM calculates if
the engine is knocking due to camshaft and
crankshaft sensor signals regarding the position of the
engine in the cycle. The ECM can also work out
exactly which cylinder is knocking and retards the
ignition on that particular cylinder until the knock
disappears. It then advances the ignition to find the
optimum ignition timing for that cylinder. The ECM can
adjust the timing of each cylinder for knock
simultaneously. It is possible that all eight cylinders
could have different advance angles at the same time.
If the camshaft sensor fails, the knock sensor will
continue to work, but as the engine may be running
one revolution out of sychronisation the ECM may
retard the wrong cylinder of the pair e.g. 1 instead of
6. If the knock sensor fails engine knock will not be
detected and corrected. The fault is indicated by
illumination of the malfunction indicator light (MIL) on
North American specification vehicles.Ignition coils
The electronic ignition system uses four double ended
coils. They are mounted on a bracket fitted to the rear
of the engine. The circuit to each coil is completed by
switching within the ECM, allowing each coil to charge
up and fire. Sparks are produced in two cylinders
simultaneously, one on compression stroke, the other
on exhaust stroke. Note that coil 1 feeds cylinders 1
and 6, coil 2 feeds cylinders 5 and 8, coil 3 feeds
cylinders 4 and 7, and coil 4 feeds cylinders 2 and 3.
Due to the ease of combustion in the cylinder on the
compression stroke, more energy is dissipated in that
cylinder. Coil failure will result in a lack of sparks and
misfire in the affected cylinders. The fault is indicated
by illumination of the malfunction indicator light (MIL)
on North American specification vehicles.
Injectors
A multiport fuel injection system (MFI) is used, one
injector per cylinder. Each injector consists of a small
solenoid which is activated by the ECM to allow a
metered amount of fuel to pass into the combustion
chamber. Due to the pressure in the fuel rail and the
shape of the injector orifice, the fuel squirts into the
cylinder in a fine spray to aid combustion. In the
unlikely event of injector failure a misfire will occur as
there will be no fuel to the affected cylinder. The fault
is indicated by illumination of the malfunction indicator
light (MIL) on North American specification vehicles.

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DESCRIPTION AND OPERATION REV: 09/95 Idle air control (IAC)
Idle speed is controlled by a stepper motor which
consists of two coils. When energised in the correct
sequence the coils move a plunger which opens and
closes the throttle bypass controlling the quantity of
idle air. The stepper motor controls idle speed by
moving the plunger a set distance called a step. Fully
open is zero steps and fully closed 180 steps. Failure
of the stepper motor will result in low or high idle
speed, poor idle, engine stall or non start. The fault is
indicated by illumination of the malfunction indicator
light (MIL) on North American specification vehicles.Heated oxygen sensor (HO2S)
The oxygen sensors consist of a titanium metal
sensor surrounded by a gas permeable ceramic
coating. Oxygen in the exhaust gas diffuses through
the ceramic coating on the sensor, and reacts with the
titanium wire altering the resistance of the wire. From
this resistance change the ECM calculates the
amount of oxygen in the exhaust gas. The injected
fuel quantity is then adjusted to achieve the correct
air/fuel ratio, thus reducing the emissions of carbon
monoxide (CO), hydrocarbons (HC),and oxides of
nitrogen (NO
2). Two HO2 sensors are fitted, one in
each exhaust downpipe just ahead of the catalyst.
Note that if the wiring to these sensors is crossed, the
vehicle will start and idle correctly until the sensors
reach operating temperature. Then the ECM will read
the signals from them and send one bank of cylinders
very rich and the other very weak. The engine will
misfire, have a rough idle and emit black smoke, with
possible catalyst damage.
In the event of sensor failure, the system will default to
'open loop'. Operation and fuelling will be calculated
using signals from the remaining ECM inputs.
The fault is indicated by illumination of the malfunction
indicator light (MIL). ECM diagnostics also uses HO2
sensors to detect catalyst damage, misfire and fuel
system faults.
North American vehicles have two extra HO2 sensors
mounted one after each catalyst. These are used to
determine whether the catalysts are operating
efficently.
CAUTION: Although robust within the
vehicle environment, HO2 sensors are
easily damaged by dropping, excessive
heat and contamination. Care must be exercised
when working on the exhaust system not to
damage the sensor housing or tip.

SFI
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DESCRIPTION AND OPERATION REV: 09/95 Fuel pressure regulator
The fuel pressure regulator is located at the rear of
the engine in the fuel rail. It consists of a fuel inlet,
outlet, vacuum port and internal diaphragm.
When the engine is under high manifold depression,
the applied vacuum sucks the diaphragm of its seat,
allowing fuel to return to the tank, resulting in a lower
fuel pressure. This is necessary because the high
depression will try to suck the fuel from the injector,
resulting in overfuelling if the pressure remained
constant. Failure will result in a rich mixture at idle but
normal at full load, or a rich mixture resulting in engine
flooding, or a weak mixture. Although the fault will not
illuminate the MIL, faults caused by the failure may be
indicated.Relay module
The engine management system employs a relay
module, which houses the main relay and the fuel
pump relay.
Main relay
The main relay supplies the power feed to the ECM
with a tap off to feed the fuel injectors (8 amps) and
air flow sensor (4 amps). This relay is controlled by
the engine management ECM. This enables the ECM
to remain powered up after ignition is switched off.
During this 'ECM power down routine' the ECM
records all temperature readings and powers the
stepper motor to the fully open position. Failure of this
relay will result in the engine management ECM not
being switched on resulting in engine not starting due
to absence of fuel and ignition.
Fuel pump relay
The fuel pump relay is fed from the ignition relay and
controlled by the engine management ECM. The relay
is activated in ignition key position 2 to prime the fuel
system for a period of time controlled by the ECM.
Failure of this relay will result in no fuel pressure.
Inertia switch
The inertia switch isolates the power supply to the fuel
pump in the event of sudden deceleration. The inertia
switch is located in the engine compartment. It is reset
by depressing the central plunger at the top of the
switch.

19FUEL SYSTEM
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DESCRIPTION AND OPERATION ADD: 09/95 ENGINE MANAGEMENT SYSTEM COMPONENT
LOCATION - ADVANCED EVAPS
1.Engine control module (ECM)
2.Ignition coils
3.Fuel pressure regulator
4.Mass air flow (MAF) sensor
5.Relay module
- Main relay
- Fuel pump relay
6.Engine coolant temperature (ECT) sensor
7.Camshaft position (CMP) sensor
8.Throttle position (TP) sensor