Peugeot 405 Manual

Fuel injection systems - general information
Fuel/exhaust systems - multi-point fuel injection models / Fuel injection systems - general information


Note: On later models the fuel injection ECU is of the Уself-learningФ 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 2500 to 3500 rpm region.

Bosch L3.1 (Jetronic) system 1 The Bosch L3.1 fuel injection system is of the intermittent type operating under low pressure. Fuel is drawn from the rearmounted fuel tank by an externally-mounted fuel pump and delivered through an in-line filter to the injectors. A pressure regulator mounted on the outlet side of the fuel rail, and connected by pipe to the inlet manifold to sense vacuum, maintains a constant pressure at the injectors according to the depression in the inlet manifold, returning excess fuel to the fuel tank.

2 A pulse damper on the inlet side of the fuel rail damps out the pressure pulses caused by the operation of the injectors.

3 The electronic control unit (ECU) and airflow meter are mounted on the air filter housing. The ECU uses signals from various sensors to determine the opening period of the injectors for any given engine operating condition. The inputs are as follows.

a) Amount of air being drawn in by the engine via the airflow meter.

b) Inlet air temperature via the thermistor mounted in the airflow meter.

c) Engine speed and angular position via the injection (coolant) thermistor.

d) Throttle position via the throttle switch unit.

4 The injectors operate simultaneously, spraying fuel onto the inlet side of the inlet valves.

5 A supplementary air device is fitted to the system to compensate for the extra fuel required during cold start conditions.

Bosch LU2-Jetronic system 6 The principle of operation of the LU2- Jetronic system is similar to that described for the L3.1-Jetronic system but with the following differences.

a) A single-barrel throttle body is fitted.

b) An oxygen sensor is fitted.

c) A catalytic converter is fitted.

7 The most significant difference is that the LU2-Jetronic system incorporates an oxygen sensor in the exhaust system, which enables the electronic control unit to carry out fine fuel/air mixture adjustment to allow the use of a catalytic converter.

Bosch Motronic MP3.1 system 8 The principle of operation of the Motronic MP3.1 system is similar to that described for the L3.1-Jetronic system but with the following differences.

a) The ECU controls the ignition system in addition to the fuel injection system, providing an integrated engine management system.

b) A static (distributorless)ignition system is used.

c) An inlet air temperature sensor and a manifold absolute pressure (MAP) sensor are used in place of the airflow meter.

d) An engine speed/position sensor is used to provide information on engine speed and crankshaft position.

Bosch Motronic M1.3 system 9 The principle of operation of the Motronic M1.3 system is similar to that described for the L3.1-Jetronic system but with the following differences.

a) The ECU controls the ignition system and the fuel injection system, providing an integrated engine management system.

b) An engine speed/position sensor is used to provide information on engine speed and crankshaft position.

c) The ECU controls the idle speed under all engine operating conditions, via an idle speed control valve. No supplementary air device is fitted.

d) An oxygen sensor is fitted to enable the ECU to control the air/fuel mixture very accurately, allowing the use of a catalytic converter.

e) A knock sensor, mounted in the cylinder block is used to detect the onset of engine knock, or pre-ignition. This enables the ECU to select the optimum ignition advance for the prevailing engine operating conditions without risk of damage to the engine.

Bosch Motronic ML4.1 system 10 The principle of operation of the Motronic ML4.1 system is similar to that described for the L3.1-Jetronic system but with the following differences.

a) The ECU incorporates a cold start function and a fault memory.

b) The mixture adjustment by-pass screw is replaced by an adjustment screw on the throttle potentiometer.

c) The throttle housing has a double body.

d) Idle speed is maintained at a predetermined level (regardless of load) by an idle speed valve.

Bosch Motronic MP5.1 system 11 The Bosch Motronic MP5.1 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 5 for detaisl on the ignition side of the system; the fuel side of the system operates as follows.

12 The fuel pump (which is immersed in the fuel tank) supplies fuel from the 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. When the optimum operating pressure of the fuel system is exceeded, the regulator allows excess fuel to return to the tank.

13 The electrical control system consists of the ECU, along with the following sensors: a) Throttle potentiometer - informs the ECU of the throttle 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 Part D of this Chapter).

e) Crankshaft sensor - informs the ECU of crankshaft position and speed of rotation.

f) Manifold Absolute Pressure (MAP) sensor - informs the ECU of the load on the engine (expressed in terms of inlet manifold vacuum).

g) Vehicle speed sensor - informs the ECU of the vehicle speed.

14 All the above signals are analysed by the ECU which selects the fuelling response appropriate to those values. The ECU controls the fuel injectors (varying the pulse width - the length of time the injectors are held open - to provide a richer or weaker mixture, as appropriate). The mixture is constantly varied by the ECU, to provide the best setting for cranking, starting (with either a hot or cold engine), warm-up, idle, cruising and acceleration.

15 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.

16 The ECU also controls the exhaust and evaporative emission control systems, which are described in Part D of this Chapter.

17 An electric heating element is fitted to the throttle housing; 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.

18 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. In this event, it ignores the abnormal 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 come on, and the relevant fault code will be stored in the ECU memory.

19 If the warning light comes on, the vehicle should be taken to a Peugeot dealer at the earliest opportunity. A complete test of the engine management system can then be carried out, using a special electronic diagnostic test unit which is simply plugged into the systemТs diagnostic connector.

Magneti Marelli 8P system 20 The Magneti Marelli 8P engine management (fuel injection/ignition) system is very similar in operation to the Bosch MP5.1 system described above, apart from the idle speed control system.

21 On the Magneti Marelli system, the idle speed is controlled by the ECU via a stepper motor fitted to the throttle housing. The motor has a pushrod controlling 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 housing passage, so controlling the idle speed. The bypass passage is also used as an additional air supply during cold starting.


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