Discovery 2. Manual — part 78

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-41

Input/Output
Input to the low tension side of the ignition coils comes from Fuse 14 located in the passenger compartment fuse box.
This fuse provides battery power for two ignition coils.

It is possible to test both primary and secondary coils of the ignition coils for resistance using a multimeter as follows:

l

Expected primary coil resistance: 0.5

±

0.05

Ω

at 20

°

C (68

°

F).

l

Expected secondary coil resistance: 13.3

±

1.3 k

Ω

at 20

°

C (68

°

F).

The ECM provides the earth control for each coil on separate pins as follows:

LH Bank (cylinders 1, 3, 5, 7)

l

Cylinder 1 - pin 6 of connector C0638 of the ECM multiplug.

l

Cylinder 3 - pin 2 of connector C0638 of the ECM multiplug.

l

Cylinder 5 - pin 8 of connector C0638 of the ECM multiplug.

l

Cylinder 7 - pin 7 of connector C0638 of the ECM multiplug.

RH Bank (cylinders 2, 4, 6, 8)

l

Cylinder 2 - pin 2 of connector C0638 of the ECM multiplug.

l

Cylinder 4 - pin 7 of connector C0638 of the ECM multiplug.

l

Cylinder 6 - pin 6 of connector C0638 of the ECM multiplug.

l

Cylinder 8 - pin 8 of connector C0638 of the ECM multiplug.

The ignition coil can fail the following ways or supply incorrect signal:

l

Coil open circuit.

l

Short circuit to vehicle supply.

l

Short circuit to vehicle earth.

l

Faulty component.

In the event of ignition coil failure any of the following symptoms may be observed:

l

Engine misfire on specific cylinders.

l

Engine will not start.

ENGINE MANAGEMENT SYSTEM - V8

18-2-42 DESCRIPTION AND OPERATION

Knock Sensor (KS)

The ECM uses two knock sensors located between the centre two cylinders of each bank to detect pre-ignition. The
knock sensors consist of piezo ceramic crystals that oscillate to create a voltage signal. During pre-ignition the
frequency of crystal oscillation increases, which alters the signal output to the ECM. The ECM compares the signal
to known signal profiles in its memory. If pre-ignition is detected the ECM retards ignition timing for a number of cycles.
If no more pre-ignition is detected, the timing is gradually advanced to the original setting.

The ignition is calibrated to run on 95 RON premium fuel, but the system will run satisfactorily on 91 RON regular fuel.
If the vehicle is refuelled with a lower grade fuel, some audible detonation will initially be heard. This is non-damaging
and ceases when the system adaption is completed.

Input/Output
Because of the nature of its operation, the knock sensors do not require any electrical input source. The KS output
for LH bank (cylinders 1, 3, 5, 7) is measured via pin 49 of connector C0636 of the ECM. The KS output for RH bank
(cylinders 2, 4, 6, 8) is measured via pin 36 of connector C0636 of the ECM. Both knock sensors have a screened
earth to protect the integrity of the sensor signals. The KS earth for LH bank (cylinders 1, 3, 5, 7) is via pin 48 of
connector C0636 of the ECM. The KS earth for RH bank (cylinders 2, 4, 6, 8) is via pin 35 of connector C0636 of the
ECM.

The connector and sensor terminals are gold plated for corrosion and temperature resistance, care must be exercised
while probing the connector and sensor terminals.

The KS can fail the following ways or supply incorrect signal:

l

Sensor open circuit.

l

Short circuit to vehicle battery supply.

l

Short circuit to vehicle earth.

l

Faulty component.

l

Incorrectly tightened sensor.

In the event of a KS signal failure any of the following symptoms may be observed:

l

KS disabled, the ECM refers to a 'safe ignition map'.

l

Rough running.

l

Engine performance concern.

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-43

The ECM performs the following diagnostic checks to confirm correct knock sensor operation:

l

KS signal level is less than the minimum threshold (dependent on engine speed) – the engine must be running,
coolant temperature above 60

°

C (140

°

F), number of camshaft revolutions since start greater than 50 and the KS

signal profile must be less than the threshold value at a given engine speed for a fault condition to be flagged

l

KS signal is greater than the maximum threshold (dependent on engine speed) – the engine must be running,
coolant temperature above 60

°

C (140

°

F), number of camshaft revolutions since start greater than 50 and the KS

signal profile must be greater than the threshold value at a given engine speed for a fault condition to be flagged

l

Error counter for verification of knock internal circuitry exceeded – the engine must be running, coolant
temperature above 60

°

C (140

°

F), number of camshaft revolutions since start greater than 50 and the error

counter greater than the threshold value at a given engine speed for a fault condition to be flagged

Should a malfunction of the component occur the following fault codes may be evident and can be retrieved by
TestBook:

Spark plugs
The spark plugs are platinum tipped on both centre and earth electrodes. The platinum tips give a long maintenance
free life.

Cleaning or resetting the spark plug gap is not recommended as this could result in damaging the platinum tips and
thereby reducing reliability.

The misfire detection system will malfunction and store erroneous codes if the incorrect spark plugs are used.

Input/Output
The ignition coils provide a voltage to the spark plugs via the ht leads. The cylinder head via the individual thread of
each spark plug provides the earth path.

The spark plugs can fail in the following ways:

l

Faulty component.

l

Connector or wiring fault.

l

Breakdown of high tension lead causing tracking to chassis earth.

l

Incorrect spark plugs fitted.

In the event of a spark plug failure, misfire on specific cylinder may be observed:

P Code

J2012 Description

Land Rover Description

P0327

Knock sensor 1 circuit low input (bank 1 or single
sensor)

LH bank signal less than threshold determined from
ECM model above 2200 rev/min

P0328

Knock sensor 1 circuit high input (bank 1 or
single sensor)

LH bank signal greater than threshold determined from
ECM model above 2200 rev/min

P0332

Knock sensor 2 circuit low input (bank 2)

RH bank signal less than threshold determined from
ECM model above 2200 rev/min

P0333

Knock sensor 2 circuit high input (bank 2)

RH bank signal greater than threshold determined from
ECM model above 2200 rev/min

ENGINE MANAGEMENT SYSTEM - V8

18-2-44 DESCRIPTION AND OPERATION

High tension (ht) leads

The ht leads are located on top of the engine, below the plenum chamber. Their function is to transfer the ht voltage
generated by the ignition coils to the spark plugs in the engine.

Input/Output
The input to the ht lead is ht voltage from the ignition coil pack. The ht lead then supplies this voltage to the spark
plug. Output ht voltage is used by the spark plugs to ignite the air/fuel mixture in the combustion chamber.

The ht leads can fail in the following ways:

l

Connector/ Wiring fault.

l

Faulty component causing spark tracking to chassis earth.

l

Damage to ht leads during component removal.

In the event of a ht lead failure the following symptom may be observed:

l

Misfire on specific cylinder.

All ignition system related faults are diagnosed by the misfire detection system and its fault codes.

Hill Decent Control (HDC)
Refer to Brakes for description of the hill descent control.

+

BRAKES, DESCRIPTION AND OPERATION, Description.

High/Low ratio switch
Refer to Transfer Box for description of the high/ low ratio switch transfer box components.

+

TRANSFER BOX - LT230SE, DESCRIPTION AND OPERATION, Description.