Discovery 2. Manual - part 489

 

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Discovery 2. Manual - part 489

 

 

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-35

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:

l

1 and 6.

l

8 and 5.

l

4 and 7.

l

3 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: 

l

Engine speed.

l

Engine load.

l

Engine temperature.

l

Knock control.

l

Automatic gearbox shift control.

l

Idle 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.

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.

ENGINE MANAGEMENT SYSTEM - V8

18-2-36 DESCRIPTION AND OPERATION

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 

 at 20 

°

C (68 

°

F).

l

Expected secondary coil resistance: 13.3 

±

 1.3 k

 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.

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.

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-37

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.

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:

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

18-2-38 DESCRIPTION AND OPERATION

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:

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.

 

 

 

 

 

 

 

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