Fuel injection systems — general information (Peugeot 106)

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.

Magneti Marelli 1 AP system

The Magneti Marelli 1 AP engine management (fuel injection/ignition) system incorporates a closed-loop catalytic converter and an evaporative emission control system and complies with the very latest emission control standards. Refer to Chapter 5B for information on the ignition side of the system; the fuel side of the system operates as follows.

The fuel pump supplies fuel from the tank to the fuel rail, via a replaceable cartridge filter mounted underneath the rear of the vehicle. The pump itself is mounted inside the fuel tank, the pump motor is permanently immersed in fuel, to keep it cool. The fuel rail is mounted directly above the fuel injectors and acts as a fuel reservoir.



Fuel rail supply pressure is controlled by the pressure regulator, mounted at the end of the fuel rail or, on later models, integrated into the fuel pump assembly. The regulator contains a spring-loaded valve, which lifts to allow excess fuel to return to the tank when the optimum operating pressure of the fuel system is exceeded (eg during low speed, light load cruising).

The fuel injectors are electromagnetic pintle valves, which spray atomised fuel into the combustion chambers under the control of the engine management system ECU. There are four injectors, one per cylinder, mounted in the inlet manifold close to the cylinder head. Each injector is mounted at an angle that allows it to spray fuel directly onto the back of the inlet valve. The ECU controls the volume of fuel injected by varying the length of time for which each injector is held open.

The fuel injection system is of the semi-sequential type, whereby fuel is injected into each cylinder's inlet tract twice per engine cycle; once during the power stroke and once during the induction stroke.

The electrical control system consists of the ECU, along with the following sensors:

• 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 housing.
• 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) Manifold Absolute Pressure (MAP) sensor - informs the ECU of the load on the engine (expressed in terms of inlet manifold vacuum).
• f) Crankshaft sensor - informs the ECU of engine speed and crankshaft angular position.
• g) Vehicle speed sensor - informs the ECU of the vehicle speed.
• h) Knock sensor - informs the ECU of preignition (detonation) within the cylinders.

Signals from each of the sensors are compared by the ECU and, based on this information, the ECU selects the response appropriate to those values and controls the fuel injectors (varying the pulse width - the length of time the injectors are held open - to provide a richer or weaker air/fuel mixture, as appropriate). The air/fuel mixture is 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 fitted to the throttle body. The stepper motor pushrod controls the amount of air passing through a by-pass drilling at the side of the throttle. When the throttle valve is closed (accelerator pedal released), the ECU uses the motor to alter the position of the pushrod, controlling the amount of air bypassing the throttle valve and so controlling the idle speed. The ECU also carries out "fine tuning" of the idle speed by varying the ignition timing to increase or reduce the torque of the engine as it is idling. This helps to stabilise the idle speed when electrical or mechanical loads (such as headlights, air conditioning etc) are switched on and off.

On certain models, the throttle housing is fitted with an electric heating element. The heater is supplied with current by the ECU, warming the throttle body on cold starts to help prevent icing of the throttle valve.

The exhaust and evaporative loss emission control systems are described in more detail in Chapter 4E.

If there is any 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, the erroneous sensor signal is overridden and the ECU assumes a pre-programmed "back-up" value, which will allow the engine to continue running, albeit at reduced efficiency. If the ECU enters this mode, the warning lamp on the instrument panel will be illuminated and the relevant fault code will be stored in the ECU memory.



If the warning light illuminates, 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 plugged into the system's diagnostic connector.

Magneti Marelli 8P system

The Magneti Marelli 8P engine management (fuel injection/ignition) system is very similar in operation to the Magneti Marelli 1AP system described previously but in addition, the throttle housing is fitted with an electric heating element. The heater is supplied with current by the ECU, warming the throttle body on cold starts to help prevent icing of the throttle valve.

(Article republished from the website PEUGEOTBOOK)

Magneti Marelli 4.8P system

The Magneti Marelli 4.8P engine management (fuel injection/ignition) system is an evolution of the Magneti Marelli systems described previously but in addition, the system is equipped with a secondary air injection system. This system is described in more detail in Chapter 4E.

Bosch Motronic MP3.1 system

The Bosch Motronic MP3.1 engine management (fuel injection/ignition) system is available in two different versions. On later models (fitted with the KFZ engine) the system incorporates a closed-loop catalytic converter and an evaporative emissions control system and complies to the very latest emission control standards. Earlier models (fitted with the K6B engine) are not fitted with either a catalytic converter or the evaporative emission control system. Refer to Chapter 5B for information on the ignition side of the system. The fuel side of the system operates as follows.



The fuel pump, immersed in the fuel tank, pumps fuel from the fuel tank to the fuel rail, via a filter mounted underneath the rear of the vehicle. Fuel supply pressure is controlled by the pressure regulator in the fuel rail, 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:

• 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 air cleaner housing.
• d) Crankshaft sensor - informs the ECU of the crankshaft position and speed of rotation.
• e) Manifold Absolute Pressure (MAP) sensor - informs the ECU of the load on the engine.
• f) Lambda (oxygen) sensor (KFZ engine only) - informs ECU of oxygen content of the exhaust gases (explained in greater detail in Part E of this Chapter).

All the above signals are compared by the ECU to values programmed (mapped) in its memory. Based on this information, the ECU selects the response appropriate to those values and controls the fuel injectors (varying their pulse width - the length of time the injectors are held open) - to provide a richer or weaker mixture, as appropriate. The mixture and idle speed are constantly monitored 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 an auxiliary air valve which bypasses the throttle valve. When the throttle valve is closed, the ECU controls the opening of the valve, which in turn regulates the amount of air entering the manifold and so controls the idle speed.

The throttle housing is fitted with an electric heating element; the heater is supplied with current by the ECU and warms the throttle housing on cold starts to prevent possible icing of the throttle valve.

On KFZ engine models, 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 from the system 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. 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 Motronic MP5.1 and MP 5.2 systems

1587 cc (NFY and NFZ engine) models are equipped with the Bosch Motronic MP5.1 or MP5.2 engine management (fuel injection/ignition) system. The MP5.1 system was fitted to all NFY engine models and to NFZ engine models up to approximately July 1996. The MP5.2 system was then used for a limited period on later NFZ engine models. Both systems are very similar in operation to the Magneti Marelli 1AP system described previously, but with the following differences.



The MP5.1 and MP5.2 systems employ "banked" fuel injection, where all four injectors are activated simultaneously. Fuel is injected into each cylinder's inlet tract on every engine stroke and is then drawn into the combustion chamber during the induction stroke.

On the MP5.1 system, ECU control of the engine idle speed is by means of an auxiliary air valve which bypasses the throttle valve. When the throttle valve is closed, the ECU controls the opening of the air valve, which in turn regulates the amount of air entering the manifold and so controls the idle speed.

On both systems the throttle housing is fitted with an electric heating element. The heater is supplied with current by the ECU, warming the throttle body on cold starts to help prevent icing of the throttle valve.

The MP5.1 system is not fitted with a knock sensor.

Bosch Motronic MP7.2 system

The Bosch Motronic MP7.2 engine management (fuel injection/ignition) system is very similar in operation to the Magneti Marelli 1AP system described previously. The injectors are operated "semi-sequentially", injectors No 1 and 4 being operated as one pair and injectors No 2 and 3 as the other.

Bosch Motronic MP7.3 system

Later 1360 cc (KFX) engines are fitted with a Bosch Motronic MP7.3 engine management (fuel injection/ignition) system which incorporates a secondary air injection system. The system is a development of the MP7.2 system designed to meet the next level of emission standards. The changes include the following.

• a) The system is fully "sequential" with all injectors being controlled individually.
• b) A body accelerometer sensor is fitted to measure the vertical movement of the vehicle body. The sensor informs the ECU of the quality of the road surface on which the vehicle is being driven. This ensures the ECU does not diagnose variations in engine speed due to an uneven road surface as an ignition misfire.
• c) A camshaft sensor is fitted to inform the ECU of the position of No 1 piston.
• d) An additional oxygen sensor is fitted down stream of the catalytic converter (see Part E for further information).
• e) Secondary air injection is fitted to improve exhaust emissions during warm-up (see Part E for further information).
• f) The idle speed is controlled by a stepper motor fitted to the throttle housing.

Bosch Motronic M7.4.4 system

The Bosch Motronic M7.7.4 engine management (fuel injection/ignition) system is an evolution of the Bosch systems described previously. The system is of the sequential injection type with each injector being operated individually in cylinder sequence. Secondary air injection is also fitted to improve exhaust emissions during warm-up (see Part E for further information).

Sagem S2000 system

The Sagem S2000 engine management (fuel injection/ignition) system is similar in operation to the Bosch Motronic MP7.3 system described previously. The main differences being in the software contained in the system ECU and the location of specific components.