Note. Electronic control unit (BEU) fuel injection is distinguished by the presence of a function «self-learning». This means that when the engine is running, the BEU monitors and records the settings that provide optimal engine dynamic performance under all operating conditions. When the battery is disconnected, these parameters are lost and the BEU returns to the basic settings programmed at the factory. When restarting the engine for a short time until the ECU collects data on the optimal settings, uneven engine operation, including idling, may be observed. Data collection is best done during a vehicle road test (within approximately 15 minutes), covering all speeds of the crankshaft and engine load, concentrating mainly in the range from 2500 rpm to 3500 rpm.
On all models, the functions of fuel injection and ignition are combined in a single engine management system. Systems from Bosch, Magneti Marelli and Sagem are used. For the most part, they are very similar to each other. The only significant difference lies in the BEU software and the arrangement of the relevant elements in accordance with the type of engine. Each system includes a closed-loop catalytic converter and an evaporative emission system and meets the latest emissions standards. For information on the ignition section of each system, refer to chapter 5B. The fuel system operates as described below.
The fuel pump draws fuel from the tank and delivers it to the fuel rail through a filter mounted on the side of the fuel tank. The pump is installed directly in the tank, and the pump motor is constantly immersed in the fuel, which contributes to its cooling. The fuel rail is mounted directly above the fuel injectors and acts as a fuel storage tank.
The supply pressure from the fuel rail is controlled by a pressure regulator located at the end of the fuel rail, on the fuel tank, or built into the fuel pump assembly. The regulator has a spring-loaded valve that lifts up to allow excess fuel to return to the tank when the optimum operating pressure in the fuel system is exceeded (e.g. at low speed, when driving at a constant speed with a light load).
Fuel injectors are solenoid needle valves that inject atomized fuel into the combustion chambers under the control of the ECU of the engine management system. There are four nozzles in total (one per cylinder), installed in the intake manifold close to the cylinder head. Each injector is angled to allow fuel to be injected directly onto the back of the intake valve (-ov). The ECU controls the amount of fuel injected by changing the length of time each injector stays open.
The electric control system includes the BEU and the following sensors:
- A) throttle potentiometer; it informs the BEU about the relative position of the throttle valve and the speed of opening/closing of the throttle valve;
- b) coolant temperature sensor; it informs the BEU about the relative temperature of the engine;
- V) air intake temperature sensor; it informs the BEU about the temperature of the air passing through the throttle body;
- G) oxygen sensors (lambda probes); they inform the BEU about the oxygen content in the exhaust gases (described in more detail in chapter 4D);
- d) intake manifold pressure sensor; it informs the BEU about the load on the engine (expressed in the level of vacuum in the intake manifold);
- e) crankshaft position sensor; it informs the BEU about the angular position and speed of the engine crankshaft;
- and) vehicle speed sensor; it informs the BEU about the vehicle speed;
- h) knock sensor; it informs the BEU about pre-ignition (detonation) in cylinders;
- h) camshaft position sensor (Motronic MP7.3); it informs the BEU about which cylinder is in the course of ignition:
- And) accelerator pedal position sensor (Sagem S2000 and Motronic ME7.4.4); it informs the BEU about the position and rate of change of the position of the pedal;
- To) accelerometer (Motronic MP7.3); he informs BEU about the quality of the road surface; it allows the ECU to not treat changes in engine speed due to uneven road surfaces as misfiring.
The signals from the sensors are analyzed by the BEU, which, based on this information, selects the nature of the reaction corresponding to these values, and controls the fuel injectors (by changing the pulse duration, i.e. the amount of time the injectors remain open to supply a richer or leaner air/fuel mixture, as required). The composition of the air-fuel mixture is constantly changing at the command of the ECU to provide the best settings for cranking, starting (hot or cold engine) and warming up the engine, as well as for idling the engine, driving the car at a constant speed and accelerating it.
In addition, the BEU fully controls the speed of the crankshaft in idle mode. This is done by a stepper motor mounted on the throttle body. Depending on the model, the stepper motor either controls the amount of air passing through the bypass port on the side of the throttle or directly controls the throttle position. In Sagem S2000 and Motronic ME7.4.4 systems, the sensor informs the ECU about the position and rate of change of the accelerator pedal position. The ECU then controls the throttle position with a throttle position motor integrated with the throttle body. In addition, BEU performs «fine tuning» idle speed by changing the ignition timing to increase or decrease engine torque when the engine is idling. This helps to stabilize the idle speed when electrical or mechanical loads are switched on or off (headlights, air conditioning, etc.).
The throttle body can also be equipped with an electric heating element. The heater is powered by the BEU and, when starting from a cold state, heats the throttle body, which helps to prevent throttle valve icing.
Emission reduction systems, including the vapor recovery system, are described in more detail in chapter 4D.
If there are any anomalies in any of the signals received from the coolant temperature sensor, air intake temperature sensor or oxygen sensor, the ECU enters «spare» mode. If this happens, the erroneous sensor signal is ignored and the ECU assumes a pre-programmed default value that allows the engine to continue running but with reduced power. If the BEU enters this mode, the control lamp on the instrument panel turns on and the corresponding fault code is recorded in the BEU memory.
If the warning light is on, have the vehicle checked by a Peugeot/Citroen dealer or an engine diagnostician as soon as possible. The technician can perform a complete check of the engine management system using a dedicated electronic diagnostic tester that plugs into the diagnostic socket located next to the passenger compartment fuse box.