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Operation of the injection/ignition system
The Bosch Motronic ME7.3.1 system with a motorized butterfly belongs to the category of integrated systems with:
ignition
sequential and phased electronic injection.
The control unit controls the air flow rate at the rotation speed set through the electronic throttle.
The control unit controls the moment of ignition with the advantage of keeping the engine running smoothly as the ambient parameters and loads applied vary.
The control unit controls and manages fuel injection so that the stoichiometric ratio (air/fuel) is always at the optimum value.
The main operating principles of the sytem are basically as follows:
self-learning;
system self-adaptation;
autodiagnosis;
recognition of the Alfa Romeo CODE (Immobilizer);
control of cold starting;
control of combustion - Lambda sensors;
control of knock;
control of mixture enrichment during acceleration;
fuel cut-off with the accelerator pedal released;
fuel vapour recovery;
control of the maximum rpm;
control of the fuel pump;
connection to the climate control system;
recognition of cylinder position;
control of the optimum injection time for each cylinder;
adjustment of ignition advance values;
management of the idle speed (also according to the battery voltage);
control of the electric fans;
connection with ABS control unit;
connection with the instrument panel;
torque management;
fuel system control;
catalyzer control;
misfire control;
Lambda sensors control.
Fuel injection system
The essential conditions that must always be met in the preparation of the air-fuel mixture for the correct operation of controlled-ignition engines are mainly:
the 'metering' (air/fuel ratio) should constantly be kept as close as possible to the stoichiometric ratio, so as to ensure the maximum conversion capacity for the catalytic converter (max. efficiency).
the 'homogeneity' of the mixture, consisting of petrol, diffused as finely and evenly as possible in the air.
The information processed by the control unit for controlling optimum metering is received in the form of electrical signals emitted by:
air flow meter and air temperature sensor, for the exact quantity of air drawn in
rpm sensor which produces an alternating, single-phase signal whose frequency indicates the engine rpm. This signal is used by the control unit for checking MISFIRE.
throttle potentiometer, to recognize the acceleration conditions requested
coolant temperature sensor located on the thermostat
Lambda sensors to determine the oxygen content of the exhaust gases and, through the downstream sensor, to diagnose the efficiency of the catalyzers.
Ignition system
The ignition is of the inductive discharge type, distributorless, with power modules located in the fuel injection control unit.
In the ignition system each coil supplies the spark plugs for the appropriate cylinder.
The advantages of this solution are:
less electrical overload;
guarantee of constant discharge at each spark plug.
Stored in the control unit, there is a map containing the entire set of optimum ignition advance values (for the cylinder at the power stroke) that the engine can adopt in relation to the rpm and required engine load.
The control unit corrects the advance values mainly in accordance with:
engine coolant temperature
intake air temperature
knock
throttle valve position
The information which the control unit processes to operate the ignition coils is received by means of electrical signals emitted by the:
air flow meter and air temperature sensor, for the exact quantity of air drawn in
rpm sensor, which generates an alternating single-phase signal whose frequency indicates the engine rpm
knock sensor (on the rear of the engine block between the 2nd and 3rd cylinders) which recognizes which cylinder is knocking and corrects its ignition advance
throttle position potentiometer, to recognize minimum, partial opening and full load conditions
timing sensor.
OPERATION
Operating strategies
Self-learning
The control unit implements the self-learning mode in the following conditions:
removing-refitting or replacement of the injection control unit
removing-refitting or replacement of the throttle body integrated with D.V.L.
removing-refitting or replacement of the rpm sensor/flywheel, for recognizing misfire.
The values memorized by the control unit are preserved if the battery is disconnected.
System self-adaption
The control unit has a self-adaption function which recognizes changes in the engine which occur as a result of bedding-in and ageing processes of both components and the engine itself.
These changes are stored in the form of modifications to the basic mapping, and their purpose is to adapt the operation of the system to the gradual alterations in the engine and components compared with their characteristics when new.
This self-adaptation function also makes it possible to even out inevitable differences (due to production tolerances) in any replaced components.
From the exhaust gas analysis, the control unit changes the basic mapping in relation to the original characteristics of the new engine.
The self-adaptation parameters are not cancelled if the battery is disconnected.
Self-testing
The control unit autodiagnostic system controls the correct operation of the system and signals any faults by means of an (MIL) warning light in the instrument panel which has a standardized European colour and ideogram. This warning light signals both engine management faults and problems detected by the EOBD strategies.
The (MIL) warning light operating logic is as follows:
with the ignition key in the ON position, the warning light comes on and remains on until the engine has been started up. The control unit's self-test system checks the signals coming from the sensors, comparing them with the permitted limits:
Signalling of faults during engine starting:
the failure of the warning light to go out once the engine has been started up means that there is an error memorized in the control unit.
Fault indication during operation
the warning light flashing indicates possible damage to the catalyzer due to misfire.
the warning light on constantly indicates the presence of engine management errors or EOBD errors.
RECOVERY
From time to time, the control unit defines the type of recovery according to the components which are faulty.
The recovery parameters are managed by those components which are not faulty.
For some markets the warning light is red (rather than amber) and the EOBD function is not active, and the warning light only indicates faults to the fuel injection system as in preceding versions. This is achieved by a specific engine management control unit (not interchangeable with the others) with modified software so as not to have the EOBD function.
Recognition of the alfa romeo code
When the control unit receives the ignition 'ON' signal, it communicates with the Alfa Romeo CODE control unit to obtain starting enablement.
Communication takes place via the dedicated bidirectional serial diagnostic line which connects the two control units.
Control of cold starting
The following occurs during cold starting:
natural weakening of the mixture because of poor turbulence of the fuel particles at low temperatures
reduced fuel evaporation
condensation of the fuel on the inner walls of the inlet manifold
increased viscosity of the lubricant oil.
The electronic control unit recognizes this condition and corrects the fuel injection time in accordance with:
coolant temperature
intake air temperature
battery voltage
engine rpm.
The ignition advance depends solely on the engine rpm and the coolant temperature.
Whilst the engine is warming up, the electronic control unit operates the idle speed actuator, which determines the quantity of air required to guarantee that the engine speed is sustained.
The rpm is made to decrease in proportion to the increase in temperature of the engine until the optimum value with the engine up to temperature is obtained.
Check on combustion - lambda sensors
In EOBD systems the Lambda sensors, which are all the same type, are located upstream of the catalyzer and downstream of the catalyzer. The upstream sensors carry out the check on the mixture strength known as the 1st loop (upstream sensor closed loop). The sensor downstream of the catalyzer is used for the catalyzer diagnosis and for finely modulating the 1st loop control parameters. With this in mind, the adjustment of the second loop is designed to recover both production differences and those in the response of the upstream sensors which may occur as a result of ageing and pollution. This control is known as the 2nd loop (downstream sensor closed loop).
Check on variable valve timing and modular inlet manifold
To optimize the quantity of air drawn in by the engine, the control unit checks:
inlet timing at two angle positions
geometry of the intake manifolds with two lengths - At the maximum torque speed, the control unit sets the 'open' phase:
cam advanced by 25° engine
inlet box long ducts
At the maximum power speed, the control unit sets the 'closed' phase:
cam in normal position
inlet box short ducts.
At idle speed, the control unit sets the 'closed' phase:
cam in normal position
inlet box short ducts.
In the other engine operating conditions, the control unit selects the most suitable configuration to optimize performance - consumption - emissions.
During overrunning, the inlet ducts of the box are always 'short'.
Knock control
The control unit detects the presence of knocking by processing the signal coming from the relevant sensor.
The control unit continuously compares the signals coming from the sensor with a threshold value, which, in turn, is continuously updated to take account of background noise and ageing of the engine.
The control unit is therefore capable of detecting the presence of detonation (or the onset of detonation) in each individual cylinder and reduces the ignition advance for the cylinder concerned (in steps of 3 degrees up to a maximum of 6 degrees) until the phenomenon disappears. The advance is then gradually restored to the basic value (in steps of 0.8 degrees).
Under acceleration conditions, a higher threshold is used to take account of the increased engine noise under such conditions.
The knock control strategy also has a self-adaptation function, which memorizes the reductions in advance that may be repeated continuously, so as to adjust the mapping to the different conditions now affecting the engine.
Control of enrichment during acceleration
If during the acceleration demand, the variation in the air flow meter signal exceeds a predefined increment, the control unit increases the fuel injection time so that the required rpm is reached rapidly.
