Defender. Manual — part 143
The ECM is connected to the engine sensors which allow it to monitor the engine operating conditions. The ECM
processes these signals and decides the actions necessary to maintain optimum engine performance in terms of
driveability, fuel efficiency and exhaust emissions. The memory of the ECM is programmed with instructions for how to
control the engine, this known as the strategy. The memory also contains data in the form of maps which the ECM uses
as a basis for fueling and emission control. By comparing the information from the sensors to the to the data in the
maps, the ECM is able to calculate the various output requirements. The ECM contains an adaptive strategy which
updates the system when components vary due to production tolerances or ageing.
The ECM receives a vehicle speed signal . Vehicle speed is an important input to the ECM strategies. The frequency of
this signal changes according to road speed.
CRANKSHAFT POSITION SENSOR (CKP)
The CKP sensor is located at the rear of the engine block on the left hand side. The sensor tip is aligned with a magnetic
trigger which is attached to the crankshaft. The reluctor is a press fit on the end of the crankshaft. The trigger wheel
must be carefully aligned to the crankshaft to ensure correct timing. The sensor produces a square wave signal, the
frequency of which is proportional to engine speed.
The ECM monitors the CKP sensor signal and can detect engine over-speed. The ECM counteracts engine over-speed by
gradually fading out speed synchronized functions. The CKP sensor is a Hall effect sensor. The sensor measures the
magnetic field variation induced by the magnetized trigger wheel.
The trigger wheel has two missing teeth representing 12º of crankshaft rotation. The two missing teeth provide a
reference point for the angular position of the crankshaft.
When the space with the two missing teeth pass the sensor tip, a gap in the signal is produced which the ECM uses to
determine the crankshaft position. The air gap between the sensor tip and the ring is important to ensure correct
signals are output to the ECM. The recommended air gap between the CKP sensor and the trigger wheel is 0.4 mm- 1.5
mm.
The ECM uses the signal from the CKP sensor for the following functions:
Synchronisation.
Determine fuel injection timing.
Enable the fuel pump relay circuit (after the priming period).
Produce an engine speed signal which is broadcast on the controller area network (CAN) bus for use by other
systems.
CMP
The CMP is located towards the rear of the left hand side of the cylinder head. The sensor tip protrudes through the face
to pick up on the reluctor behind the camshaft pulley.
The sensor is a Hall effect sensor which used by the ECM at engine start-up to synchronize the ECM with the CKP sensor
signal. The ECM does this by using the CMP sensor signal to identify number one cylinder to ensure the correct injector
timing. Once the ECM has established the injector timing, the CMP sensor signal is no longer used.
The CMP sensor receives a 5V supply from the ECM. Two further connections to the ECM provide ground and signal
output.
If a fault occurs, an error is registered in the ECM. Two types of failure can occur; camshaft signal frequency too high or
total failure of the camshaft signal. The error recorded by the ECM can also relate to a total failure of the crankshaft
signal or crankshaft signal dynamically implausible. Both components should be checked to determine the cause of the
fault.
If a fault occurs with the CMP sensor when the engine is running, the engine will continue to run but the ECM will
deactivate boost pressure control. Once the engine is switched off, the engine will crank but will not restart while the
fault is present.
GLOW PLUGS
Four glow plugs are located in the cylinder head, on the inlet side. The glow plugs and the glow plug relay are a vital
part of the engine starting strategy. The glow plugs heat the air inside the cylinder during cold starts to assist
combustion. The use of glow plugs helps reduce the amount of additional fuel required on start-up, and consequently
reduces the emission of black smoke. The use of glow plugs also reduces the amount of injection advance required,
which reduces engine noise, particularly when idling with a cold engine.
There are three phases of glow plug activity:
Pre-heat
During crank
Post heat
The main part of the glow plug is a tubular heating element which protrudes into the combustion chamber of the engine.
The heating element contains a spiral filament encased in magnesium oxide powder. At the tip of the tubular heating
element is the heater coil. Behind the heater coil, and connected in series, is a control coil. The control coil regulates the
heater coil to ensure that it does not overheat.
Pre-heat is the length of time the glow plugs operate prior to engine cranking. The ECM controls the pre-heat time
based on engine coolant temperature (ECT) sensor output and battery voltage. If the ECT sensor fails, the ECM will use
the IAT sensor value as a default value. The pre-heat duration is extended if the coolant temperature is low and the
battery is not fully charged.
Post heat is the length of time the glow plugs operate after the engine starts. The ECM controls the post heating time
based on ECT sensor output. The post heat phase reduces engine noise, improves idle quality and reduces hydrocarbon
emissions.
When the ignition is switched on to position II, the glow plug warning lamp illuminates in the instrument cluster. The
glow-lamp is activated separately from the glow-plugs, so is not illuminated during or after start. The plugs can still be
ON when the lamp is off in these two phases.
In the event of glow plug failure, the engine may be difficult to start and excessive smoke emissions may be observed
after starting.
The glow plug warning lamp also serves a second function within the EDC system. If a major EDC system fault occurs,
the glow plug warning lamp will be illuminated until the fault is rectified. The driver must seek attention to the engine
management system at a Land Rover dealer as soon as possible.
INJECTORS
There are 4 electronic fuel injectors (one for each cylinder) located in a central position between the four valves of each
cylinder. The ECM divides the injectors into two banks of 4 with cylinders.
Each injector is supplied with pressurized fuel from the fuel rail and delivers finely atomized fuel directly into the
combustion chambers. Each injector is individually controlled by the ECM which operates each injector in the firing order
and controls the injector opening period via pulse width modulation (PWM) signals. Each injector receives a 12V supply
from the ECM and, using programmed injection/timing maps and sensor signals, determines the precise pilot and main
injector timing for each cylinder. If battery voltage falls to between 6 and 9V, fuel injector operation is restricted,
affecting emissions, engine speed range and idle speed. In the event of a failure of a fuel injector, the following
symptoms may be observed:
Engine misfire
Idle irregular
Reduced engine performance
Reduced fuel economy
Difficult starting
Increased smoke emissions.
The ECM monitors the wires for each injector for short circuit and open circuit, each injector and the transient current
within the ECM. If a defect is found, an error is registered in the ECM for the injector in question.
CHT SENSOR
The CHT sensor is located in the top hose at the coolant manifold junction. The ECT sensor provides the ECM and the
instrument cluster with engine coolant temperature status.
The ECM uses the temperature information for the following functions:
Fueling calculations
Limit engine operation if engine coolant temperature becomes too high
Cooling fan operation
Glow plug activation time.
The instrument cluster uses the temperature information for temperature gauge operation. The CHT signal is also
transmitted on the CAN bus by the instrument cluster for use by other systems.
The ECMCHT sensor circuit consists of an internal voltage divider circuit which incorporates an negative temperature
coefficient (NTC) thermistor. As the CHT rises the resistance through the sensor decreases and vice versa. The output
from the sensor is the change in voltage as the thermistor allows more current to pass to earth relative to the
temperature of the coolant.
The ECM compares the signal voltage to stored values and adjusts fuel delivery to ensure optimum driveability at all
times. The engine will require more fuel when it is cold to overcome fuel condensing on the cold metal surfaces inside
the combustion chamber. To achieve a richer air/fuel ratio, the ECM extends the injector opening time. As the engine
warms up the air/fuel ratio is leaned off.
The input to the sensor is a 5V reference voltage supplied from the voltage divider circuit within the ECM. The ground
from the sensor is also connected to the ECM which measures the returned current and calculates a resistance figure for
the sensor which relates to the coolant temperature.
The following table shows CHT values and the corresponding sensor resistance and voltage values.
Coolant Temperature Sensor Response
Temperature (Degrees Celsius)
Resistance (Kohms)
Voltage (Volts)
-40
925
4.54
-30
496
4.46
-20
277
4.34
-10
160
4.15
0
96
3.88
10
59
3.52
20
37
3.09
30
24
2.62
40
16
2.15
50
11
1.72
60
7.5
1.34
70
5.6
1.04
80
3.8
0.79
90
2.9
0.64
100
2.08
0.49
110
1.56
0.38
120
1.19
0.29
130
0.918
0.22
140
0.673
0.17
150
0.563
0.14
If the CHT sensor fails, the following symptoms may be observed:
Difficult cold start.
Difficult hot start.
Engine performance compromised.
Temperature gauge inoperative or inaccurate reading.
In the event of CHT sensor signal failure, the ECM applies a default value of 80°Celsius (176°F) coolant temperature for
Fueling purposes. The ECM will also permanently operate the cooling fan at all times when the ignition is switched on, to
protect the engine from overheating.
OIL PRESSURE SWITCH
The oil pressure switch, located in the oil cooler assembly, connects a ground input to the instrument cluster when oil
pressure is present. The switch operates at a pressure of 0.15 to 0.41 bar (2.2 to 5.9 Psi).
FUEL RAIL PRESSURE SENSOR
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