Defender Electric Diagrams. Instruction - page 12

CIRCUIT OPERATION

DEFENDER 90 NAS

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STARTING - OPERATION

When the ignition switch is in position 'II', power flows across the switch to fuse 20 of the
passenger compartment fuse box (C581-13) on the white wire. Fuse 20 (C581-20) is
connected to the fuel pump relay winding in the ECM relay module (C154-2) by the
white/green wire. The fuel pump relay winding (C154-1) is grounded through the ECM
(C634-24) on the blue/purple wire. The ECM grounds the fuel pump relay winding for a
short time when the ignition is switched to position 'II', and continuously during cranking
and while the engine in running. With the fuel pump relay winding energized, the fuel
pump relay closes and power from fuse 6 (C575-2) of the engine compartment fuse box
flows through the fuel pump relay (C157-7) on the purple/white wire. The fuel pump relay
(C157-4) is connected to the inertia switch (C123-3) by the white/purple wire. Assuming
the inertia switch is closed, power flows across the switch (C123-1) to the fuel pump
(C113-4) on the white/purple wire. The fuel pump is grounded on a black wire.

Turning the ignition switch to the crank position 'III', allows power to flow across the
switch (C90-1) to the starter relay winding (C151-85) on the white/red wire. The starter
relay winding is grounded on the black/yellow wire to the starter inhibitor/reverse switch
(C69-5). With the gear selector lever in park or neutral, the route to ground is from the
inhibitor switch (C69-4) to the immobilization unit (C57-10) on the black/orange wire.
Assuming the engine has been mobilized, the immobilization unit is grounded on a black
wire. With the starter relay energized, power from fusible link 5 of the engine
compartment fuse box (C570-2) flows across the relay (C151-87) on the brown wire.
The starter relay is connected to the starter motor solenoid (C179-1) by the brown/red
wire. The starter motor solenoid is grounded through the starter motor fixing. With the
starter motor solenoid energized, feed from the battery is connected to the starter motor
(C178-1) through the starter solenoid on a red wire.

CIRCUIT OPERATION

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DEFENDER 90 NAS

GENERIC ENGINE MANAGEMENT SYSTEM (GEMS)

DESCRIPTION

GEMS is the engine management system utilized by the vehicle to control both electronic
ignition and fuel injection systems. It is able to alter ignition and fuelling settings to
ensure that the engine is operating at its optimum performance for the prevailing
conditions. The ECM receives signals from sensors located around the engine and uses
the data to control the fuel quantity, fuel injection timing and ignition timing in order to
achieve optimum combustion of the fuel mixture in each cylinder.

The main features of the system are as follows:

A single engine control module (ECM) controls the fuel injection system and
ignition system. The ECM incorporates short circuit protection and can store
intermittent faults on certain inputs. TestBook can be used to interrogate the ECM
for the stored fault codes.

Fuel is injected sequentially. That is, when the relevant piston is on the intake stroke
and the intake valve is open.

The ECM is electronically coded and prevents the engine being started unless it
receives the correct code from the engine immobilization ECU.

Detection and correction of engine knock on individual cylinders. The ignition
timing of each cylinder can be varied independently to the other cylinders and
ensures that knock on one cylinder is eliminated without a detrimental effect on the
ignition timing of the other cylinders.

A diagnostic connector, located below the passenger compartment fuse box, allows
engine tuning or fault diagnosis to be carried out using TestBook.

If certain inputs to the ECM fail, a back-up facility enables the engine to continue
running, although at a reduced level of performance.

IGNITION SYSTEM

The ignition system utilizes a direct ignition system (DIS) negating the need for a
distributor. The system comprises 4 double ended coils operating the wasted spark
principle. The circuit to each coil is controlled by the ECM. When a coil fires, a spark is
produced in two cylinders, however, as the resistance is higher in the cylinder on the
compression stroke, more spark energy is dissipated in this cylinder.

CIRCUIT OPERATION

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The ECM determines the optimum ignition timing based on signals from the following
sensors:

Crankshaft position (CKP) sensor - engine speed and crankshaft position

Camshaft position (CMP) sensor - camshaft position

Intake air temperature (IAT) sensor - inlet air temperature

Knock sensors - engine vibration, detonation

The engine management system uses no centrifugal or vacuum advance, timing is
controlled entirely by the ECM.

Crankshaft position (CKP) sensor

The CKP sensor signal is used as the basis for ignition timing. It informs the ECM that
the engine is turning, the speed the engine is turning and position of the engine in its
cycle.

The sensor uses the principle of magnetic induction to generate the signal. A reluctor ring,
attached to the engine flywheel, has a series of teeth spaced at 10° intervals, with one
tooth missing at 20° after TDC. The reluctor ring rotates with the engine, in close
proximity to the CKP sensor. As each tooth of the reluctor ring passes the sensor, it
disturbs the magnetic field of the sensor and a voltage is induced in the sensor coil. The
ECM calculates engine speed by counting pulses per second from the CKP sensor.
Engine position is calculated by counting pulses after missing pulse.

In the event of a sensor failure, the engine will not run.

Camshaft position (CMP) sensor

The CMP sensor is used in conjunction with the CKP sensor to inform the ECM of the
position of the engine in the 4 stroke cycle. Using the CKP sensor alone, the ECM is
unable to determine whether a cylinder is on its compression stroke or exhaust stroke.

The sensor uses the principle of magnetic induction to generate the signal. The cam
wheel has four lobes which pass in close proximity to the CMP sensor as the camshaft
rotates. The lobes disturb the magnetic field of the sensor and induce a voltage in the
sensor coil.

In the event of a sensor failure, the ECM will continue to operate normal ignition timing
using the CKP sensor signal. Engine knock detection and correction will be disabled.

CIRCUIT OPERATION

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DEFENDER 90 NAS

Inlet air temperature (IAT) sensor

The basis of the IAT sensor is a temperature dependent resistive metal strip. The
resistance of the metal strip varies considerably with temperature. When an inlet
temperature of 55 °C or higher is detected, the ECM retards the ignition timing . If the
sensor fails, the ECM assumes an inlet temperature of 50 °C.

Knock sensor

The knock sensor is a piezo-electronic accelerometer, which produces an electronic signal
related to the vibration of the engine. A knock sensor is located in each bank of
cylinders. The signal from each knock sensor is transmitted to the ECM. The ECM is
able to filter out normal engine vibrations and detect vibrations induced by engine
knock.

Using the signal from the knock sensor in conjunction with the CKP and CMP signals
enables the ECM to identify which cylinder is producing the knock and hence retard the
ignition timing of that cylinder only. The ignition timing of the cylinder producing the
knock is retarded until the knock disappears. The ECM then advances the ignition timing
to find the optimum advance angle for that cylinder. The ECM is able to perform a
similar function for each of the 8 cylinders simultaneously. It is therefore possible for all
8 cylinders to have different advance angles at any one time.

FUELLING SYSTEM

Engine fuelling is by a fully sequential, electronic fuel injection system, controlled by the
ECM. The ECM determines the timing and quantity of fuel to be injected based on
information received from the following sensors.

Crankshaft position (CKP) sensor - engine speed and crankshaft position

Camshaft position (CMP) sensor - camshaft position

Mass air flow (MAF) sensor - quantity of air entering the engine

Intake air temperature (IAT) sensor - temperature and hence density of air entering
the engine

Throttle position (TP) sensor - position of throttle and rate of change of throttle

Engine coolant temperature (ECT) sensor - coolant temperature

Engine fuel temperature (EFT) sensor - temperature of fuel rail

Heated oxygen sensor (HO2S) - oxygen content of exhaust

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