Table of contents: Bosch Monopoint A2.2 system 🠇 Bosch Monopoint MA3.0 and MA3.1…🠇 Magneti Marelli G6 system 🠇
Note: The fuel injection ECU is of the "self learning" type, meaning that as it operates, it also monitors and stores the settings which give optimum engine performance under all operating conditions. When the battery is disconnected, these settings are lost and the ECU reverts to the base settings programmed into its memory at the factory. On restarting, this may lead to the engine running/idling roughly for a short while, until the ECU has re-learned the optimum settings. This process is best accomplished by taking the vehicle on a road test (for approximately 15 minutes), covering all engine speeds and loads, concentrating mainly in the 2,500 to 3,500 rpm region.
Bosch Monopoint A2.2 system
The Bosch Monopoint A2.2 fuel injection system incorporates a closed-loop catalytic converter and an evaporative emission control system and complies with pre-1996 emission standards. The system operates as follows.
The fuel pump, immersed in the fuel tank, pumps fuel from the fuel tank to the fuel injector, via a filter mounted underneath the rear of the vehicle. Fuel supply pressure is controlled by the pressure regulator in the throttle body assembly, which lifts to allow excess fuel to return to the tank when the optimum operating pressure of the fuel system is exceeded.
The electrical control system consists of the ECU, along with the following sensors and actuators:
- a) Throttle potentiometer - informs the ECU of the throttle valve position and the rate of throttle opening/closing.
- b) Coolant temperature sensor - informs the ECU of engine temperature.
- c) Inlet air temperature sensor - informs the ECU of the temperature of the air passing through the throttle body.
- d) Lambda sensor - informs the ECU of the oxygen content of the exhaust gases (explained in greater detail in Part E of this Chapter).
- e) Throttle position switch (built into idle control stepper motor) - informs the ECU when the throttle valve is closed (ie when the accelerator pedal is released).
- f) Idle control stepper motor - controls the position of the throttle during idling to maintain a constant engine idle speed.
- g) Ignition HT coil - ECU monitors the coil low-tension (LT) circuit to determine the engine speed.
All the above signals are compared by the ECU and, based on this information, the ECU selects the response appropriate to those values and controls the fuel injector (varying its pulse width - the length of time the injector is held open - to provide a richer or weaker mixture, as appropriate). The mixture and idle speed are constantly varied by the ECU, to provide the best settings for cranking, starting (with either a hot or cold engine) and engine warm-up, idle, cruising and acceleration.
The ECU also has full control over the engine idle speed, via a stepper motor which is fitted to the throttle body. The motor pushrod rests against a cam on the throttle valve spindle. When the throttle valve is closed (accelerator pedal released), the ECU uses the motor to vary the opening of the throttle valve and so control the idle speed.
The ECU also controls the exhaust and evaporative emission control systems, which are described in detail in Part E of this Chapter.
If there is an abnormality in any of the readings obtained from either the coolant temperature sensor, the inlet air temperature sensor or the lambda sensor, the ECU enters its back-up mode. If this happens, it ignores the sensor signal and assumes a preprogrammed value which will allow the engine to continue running, albeit at reduced efficiency. If the ECU enters this back-up mode, the warning light on the instrument panel will be illuminated and the relevant fault code will be stored in the ECU memory.
If the warning light comes on, the vehicle should be taken to a Peugeot dealer at the earliest opportunity. Once there, a complete test of the engine management system can be carried out, using a special electronic diagnostic test unit which is simply plugged into the system's diagnostic connector.
Bosch Monopoint MA3.0 and MA3.1 systems
The Bosch Monopoint MA3.0 and MA3.1 engine management systems differ from the earlier A2.2 system in that they control both the fuel injection system and ignition system, thus providing full engine management under all operating conditions. Both systems incorporate a closed-loop catalytic converter and an evaporative emission control system and comply with the latest emission standards. Refer to Chapter 5B for information on the ignition side of the system.
The fuel injection side of the system is very similar to the A2.2 system described above, with the following differences.
A crankshaft sensor is fitted to the engine, to inform the ECU of engine speed and crankshaft position. The crankshaft sensor is needed since the ECU also controls the ignition side of the system and cannot use the ignition low-tension (LT) circuit to calculate engine speed. The sensor works in conjunction with a reluctor ring fixed to the rear of the flywheel. The reluctor ring originally has a total of 60 teeth, which are equally spaced at intervals of 6°. Of these 60 teeth, two adjacent teeth are removed to leave a gap of 18°. The ECU uses the reluctor ring gap to establish where TDC is and calculates engine speed from the frequency of teeth passing the crankshaft sensor.
On 1360 cc models, a vehicle speed sensor is also incorporated into the system. The vehicle speed sensor is fitted to the transmission and informs the ECU of the actual speed of the vehicle.
On the MA3.1 system an inlet manifold heater is fitted, to raise the temperature of the inlet manifold and minimise fuel condensation.
Magneti Marelli G6 system
The Magneti Marelli G6 engine management system controls both the fuel injection and ignition systems and incorporates a closed-loop catalytic converter and an evaporative emission control system to comply with the latest emission standards.
The fuel injection side of the system operates as follows. Refer to Chapter 5B for information on the ignition side of the system.
The fuel pump, immersed in the fuel tank, pumps fuel from the fuel tank to the fuel injector via a filter. Fuel supply pressure is controlled by the pressure regulator in the throttle body assembly, which lifts to allow excess fuel to return to the tank when the optimum operating pressure of the fuel system is exceeded. To reduce emissions and to improve drive ability when the engine is cold, an electrical heating element is fitted to the throttle body, to quickly warm it up on cold starts.
The electrical control system consists of the ECU, along with the following sensors and actuators:
- a) Manifold absolute pressure (MAP) sensor - informs the ECU of load on engine.
- b) Crankshaft sensor - informs the ECU of crankshaft position and engine speed.
- c) Throttle potentiometer- informs the ECU of the throttle valve position and the rate of throttle opening/closing.
- d) Coolant temperature sensor - informs the ECU of engine temperature.
- e) Inlet air temperature sensor - informs the ECU of the temperature of the air passing through the throttle body.
- f) Lambda (oxygen) sensor - informs the ECU of the oxygen content of the exhaust gases (explained in greater detail in Part E of this Chapter).
- g) Idle control stepper motor - controls the position of the throttle during idling to maintain a constant engine idle speed.
In addition, the ECU senses battery voltage (adjusting the injector pulse width to suit and using the stepper motor to increase the idle speed and, therefore, the alternator output if it is too low). The ECU has short-circuit protection and diagnostic capabilities and can both receive and transmit information via the engine management circuit diagnostic connector, thus permitting engine diagnosis and tuning by special diagnostic equipment.
All the above signals are compared by the ECU, using digital techniques, with set values pre-programmed (mapped) into its memory; based on this information, the ECU selects the response appropriate to those values and controls the ignition HT coil (see Chapter 5B) and the fuel injector (varying its pulse width - the length of time the injector is held open - to provide a richer or weaker mixture, as appropriate). The mixture, idle speed and ignition timing are constantly varied by the ECU to provide the best settings for cranking, starting (with either a hot or cold engine) and engine warm-up, idle, cruising and acceleration.
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The ECU regulates the engine idle speed via a stepper motor which is fitted to the throttle body. The motor has a pushrod which controls the opening of an air passage which bypasses the throttle valve. When the throttle valve is closed, the ECU controls the movement of the motor pushrod, which regulates the amount of air which flows through the throttle body passage and so controls the Idle speed. The bypass passage is also used as an additional air supply during cold starting.
The ECU also controls the exhaust and evaporative emission control systems, which are described in detail in Part E of this Chapter.
If there is an abnormality in any of the readings obtained from any of engine management circuit sensors, the ECU enters a back-up mode. If this happens, it ignores the sensor signal and assumes a preprogrammed value which will allow the engine to continue running, albeit at reduced efficiency. On entering the back-up mode, the engine management warning light in the instrument panel will come on, informing the driver of the fault and the relevant fault code will be stored in the ECU memory.
If the warning light comes on, the vehicle should be taken to a Peugeot dealer at the earliest opportunity. Once there, a complete test of the engine management system can be carried out, using a special electronic diagnostic test unit which is simply plugged into the system's diagnostic connector.