MG MG6 Series 2011 Service Manual page 292

Engine
When the handset is removed, theECM switches off ignition
and fuelling to stop the engine. TheECM continues to hold the
main relay in the on position until it has completed the power
down functions. Power down functions include engine cooling
and referencing the position of the throttle butterfly for the
next start up. When the power down process is completed,
theECM switches off the main relay and enters a low power
mode. During low power mode theECM will consume less
than 1mA.
If theECM suffers an internal failure, such as break down of the
processor or driver circuits, there are no back up systems or
limp home capability. If a sensor circuit fails to supply an input,
this will result in a substitute or default value being adopted
where possible. This enables the vehicle to function, but with
reduced performance.
TheECM is connected to vehicle ground using four wires. Pins
M1, M2, M4 and L4 ofECM connector EB042 are connected
to body ground. With the handset removed, theECM is
supplied with battery voltage to power the memory. The
voltage is supplied from the battery positive terminal via the
engine compartment fuselink 1 and fuse 5 to pin L1 ofECM
connector.
When the handset is docked, theECM receives battery voltage
at pin J4 of connector EB042. TheECM initiates 'wake up' by
energising the main relay. This is carried out by completing the
ground path for the relay coil which is connected to theECM
at pin A4 of connector EB042.
Fuel Quantity
TheECM controls fuel quantity by providing timed sequential
fuel injection to the inlet manifold tracts. The CMPsensor and
reluctor allows theECM to synchronise injection at cranking
speed for starting. The precise quantity of fuel delivered
is controlled by adjusting the duration of the injector open
time. To achieve optimum performance theECM is able to
'learn' the individual characteristics of an engine and adapt the
fuelling strategy to suit. This capability is known as adaptive
fuel strategy.
Adaptive fuel strategy must be maintained under all throttle
positions except:
• Cold start
• Hot start
• Wide Open Throttle WOT
All of the above throttle positions are deemed to be 'open
loop'. Open loop fuelling does not rely on information from
the HO2S, but sets the Air/Fuel Ratio (AFR) according to the
stored data, or 'map', in the ECM. During a cold start, the
ECM references the ECT sensor to calculate the appropriate
amount of fuel required to support combustion, and adjusts
the idle speed to the correct 'fast idle' value. This strategy is
Version 2.0
Engine Fuel & Management System
maintained until the HO2S reaches a high enough temperature
to provide an accurate feedback signal. The specific nature of
the other open loop conditions listed means that the HO2S
feedback is unsuitable as a control value for fuelling. Adaptive
strategy also allows the ECM to compensate for wear in engine
components and for production tolerances in sensors.
To calculate the amount of fuel to be injected into each cylinder,
theECM has to determine the quantity of oxygen available in
the cylinder. This can be calculated by processing information
from the following sensors
• TMAP sensor
• CKP sensor
• ECT sensor
• ETB
The pressure of the air in the inlet manifold will vary according
to the following factors:
• The position of the throttle pedal (driver input)
• The atmospheric pressure (altitude and weather
conditions)
• The mechanical condition of the engine (volumetric
efficiency)
The pressure in the inlet manifold, downstream of the ETB,
indicates how much air has flowed into the cylinders. This
will decrease at higher altitudes as the air becomes less dense.
This will also mean that there will be less oxygen available for
combustion of fuel.
From the above information, theECM can calculate how much
air has been induced into the cylinders. The oxygen content
is determined by adding the inlet air temperature into the
equation. By comparing these values to a fuelling map stored
in theECM memory, the amount of oxygen induced into the
cylinders can be calculated. The values obtained from theECT
sensor provide 'fine tuning' to the calculations.
To deliver the fuel theECM completes a ground path to the
injector coil, opening the injector for the precise amount
of time required for the quantity determined. The correct
cylinder order is determined by referencing the CMPsensor
during start up to synchronise theCKP sensor signal . The
fuel is injected into the inlet ports of the inlet manifold and is
drawn into the cylinder as an air and fuel mixture.
TheECM references battery voltage to adjust opening times to
suit the state of battery charge. This is required because low
battery voltage will mean slower response from the injectors,
and could give a leanerAFR than intended.
Heated Oxygen Sensor (HO2S)
The material used in the sensing element only becomes active
at around 300 °C (572 °F), therefore it is necessary to provide
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