Defender Electric Diagrams. Manual - part 13

 

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Defender Electric Diagrams. Manual - part 13

 

 

CIRCUIT OPERATION

DEFENDER 90 NAS

7

Crankshaft position (CKP) sensor   

The CKP sensor signal is used as the basis for fuel injection timing.  It informs the GEMS
that the engine is turning, the speed at which it is turning and its position in the 4 stroke
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.  

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 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 sequential fuel injection
using the CKP sensor signal.  It is possible that the injection timing will be one engine
revolution out of sequence.  

Mass air flow (MAF) sensor  

The MAF sensor is used to measure the quantity of air being drawn into the engine and
hence give an indication of the quantity of fuel to be injected to provide a stoichiometric
(chemically correct ratio) mixture strength.  

The MAF sensor is an anemometer located in the inlet air flow, upstream of the throttle
body, which uses the Hot Wire principle to determine air flow. A single metering wire is
maintained at a constant temperature. As  air flows over the wire, current is applied to the
wire to maintain the temperature at its reference temperature, the faster the air flow, the
greater the cooling effect and the greater the current required to maintain the temperature.
The current supplied to the hot wire is converted to a voltage signal and sent to the ECM.
The ECM uses the voltage signal to calculate the quantity of air being drawn into the
engine.  If the sensor fails, the ECM calculates a value dependent on throttle position,
engine speed and air temperature.  

CIRCUIT OPERATION

8

DEFENDER 90 NAS

Intake air temperature (IAT) sensor

The IAT sensor, by measuring the temperature of induction air, enables the ECM to
determine the density, and hence, the oxygen content of the air being burned in the
engine. As air temperature increases, it expands, and its density (Mass/Unit of Volume)
decreases. 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.   

Throttle position (TP) sensor   

The TP sensor measures the angle of throttle opening and the rate of change of throttle
position. The angle of throttle opening gives an indication of the quantity of air being
drawn into the engine. The rate of change of throttle angle gives an indication of rate of
acceleration demanded.  

The sensor is a rotary variable resistor mounted to the throttle butterfly spindle giving an
output of 0 to 5 volts.  

Engine coolant temperature (ECT) sensor   

The coolant temperature sensor measures the temperature of the engine coolant fluid. The
signal from the coolant sensor is used by the ECM to adjust the fuelling mixture. The
engine requires a richer mixture at lower temperatures.  

The sensor relies on a temperature dependent resistive metal strip.  The resistance of the
metal strip varies considerably with temperature and is immersed in the engine coolant
fluid.  

If the sensor fails, the ECM assumes and engine coolant figure of 80°C. The fault could
be noticeable during the engine warm up period.  

Engine Fuel Temperature (EFT) sensor  

The fuel temperature sensor measures the temperature of the fuel rail. The signal from the
sensor gives the ECM a warning of fuel vaporization and the possibility of bubbles
forming in the injectors, which may cause poor hot starting. If the ECM receives a high
fuel temperature signal during starting, the fuel injector opening period is increased to
clear any vaporization bubbles from the injectors and correct the fuelling.  When the
engine is running, fuel circulation from the fuel tank keeps the fuel rail cool.

CIRCUIT OPERATION

DEFENDER 90 NAS

9

Heated oxygen sensor (HO2S)   

4 HO2S's are fitted to the vehicle, one before and one after each catalyst.  The HO2S
comprises a titanium metal sensor surrounded by a gas permeable ceramic coating.
Oxygen permeating the ceramic coating reacts with the titanium wire, altering its
resistance.  The resistance of the sensor is directly related to the quantity of oxygen
around the sensor.  The HO2S does not function correctly until it reaches a temperature of
approximately 300°C and so a heating element is incorporated into the sensor to provide
rapid warm up after a cold start.   

The signals from the HO2S's are used by the ECM to correct the fuelling to each bank of
cylinders independently.  The 2 sensors upstream of the catalysts measure the oxygen
content of the gasses exhausted from the engine, indicating a rich or weak mixture
strength. The ECM alters the pulse width of the injectors to correct the mixture strength
and achieve a stoichiometric air/fuel ratio.  The 2 HO2S's downstream of the catalysts
measure the efficiency of the catalysts by comparing the sensor's voltage switching
frequency to that of the upstream catalysts. If the catalyst is operating efficiently, the
switching frequency of the downstream sensor will be lower than that of the upstream
sensor.   

Injectors  

The fuel injection system has 8 fuel injectors, 1 for each cylinder.  Each injector
comprises  a solenoid with a needle valve held in position by a spring.  The route to
ground for the solenoid is controlled by the ECM. When energized, the solenoid lifts the
needle valve from its seat and pressurized fuel from the fuel rail flows through the
injector. The ECM controls the amount of fuel delivered by opening the injector for
varying periods. The injector orifice is shaped to produce a fine spray of fuel which aids
combustion.  

Fuel pressure regulator  

The fuel pressure regulator is a mechanical device mounted to the fuel rail.  Its purpose is
to control the fuel rail pressure at a fixed level above inlet manifold depression, thus
ensuring that the correct amount of fuel is injected for given injector opening times.

The fuel pressure regulator contains a spring loaded diaphragm valve with pressurized
fuel on one side of the diaphragm and manifold depression acting on the other.  When fuel
rail pressure, assisted by manifold depression, overcomes the diaphragm spring load , fuel
flows past the diaphragm valve to the fuel tank, reducing fuel rail pressure.  With
manifold depression low, during hard acceleration, the fuel rail pressure must be high to
overcome the diaphragm spring load.  With manifold depression low, during coast down,
the vacuum acting on the diaphragm valve acts against the spring load and a lower fuel
rail pressure lifts the valve from its seat.  

CIRCUIT OPERATION

10

DEFENDER 90 NAS

Idle air control valve  (IACV)  

Engine idle speed is maintained by the IACV, controlled by the ECM.  With the throttle
butterfly fully closed, a small quantity of air is able to by-pass the throttle butterfly via the
base idle passage.  The ECM  monitors engine speed and load via sensors around the
engine. Should extra air be required to maintain a steady idle speed, the ECM signals the
IACV to operate a number of steps and open the throttle by-pass. The stepper motor,
integral to the IACV, operates over a range of 200 steps with the valve fully open at 200
steps and fully closed at 0 steps.   

Canister purge valve (CANPV) 

The vehicle is equipped with an evaporative emission control system designed to prevent
vapor loss from the fuel tank.  Fuel tank vapor is passed through a charcoal canister
which traps fuel vapor. The vapor trapped by the charcoal canister is drawn in to the
engine through the purge valve and burnt in the combustion chamber.  

The ECM controls the opening of the CANPV to allow venting of the charcoal canister.
The ECM pulses the valve open for short periods when the engine has reached normal
operating temperature and is turning at a speed over 1700 rpm. This is done to ensure that
the fuelling of the engine is not adversely affected during warm up or at idle. During
purge valve operation, the ECM monitors HO2S signals.  If opening the purge valve
causes the HO2S signal to indicate a leaner mixture, the ECM assumes that the charcoal
canister is empty. When the ECM senses that the charcoal canister is empty, the purge
valve is opened to prevent a build up of fuel vapor in the canister. With the purge valve
open, unmetered air is drawn into the engine through the charcoal canister. The ECM
uses the signal from the HO2S's to correct the fuelling. 

 

 

 

 

 

 

 

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