Opel Corsa B 1993–2000 Service and Repair Manual: Fuel injection system - general information

1.4 and 1.6 litre models

1. The MULTEC Central Fuel injection (CFI) system is fitted to 1.4 litre (C14NZ) and 1.6 litre (C16NZ) engine models and provides a simple method of fuel metering whereby fuel is injected into the inlet manifold by a single solenoid operated fuel injector unit. The injector unit is located centrally in the top of the throttle valve housing and this is mounted on the top of the inlet manifold. The length of time for which the injector remains open determines the quantity of fuel reaching the cylinders for combustion. The electrical signals which determine the fuel injector opening duration are calculated by the Electronic Control Unit (ECU) from the information supplied by a network of sensors.

The fuel pressure is regulated mechanically.

2. The signals fed to the ECU include inlet manifold vacuum from the Manifold Absolute Pressure (MAP) sensor; engine speed and crankshaft position from the distributor; road speed from a sensor at the base of the speedometer cable; the position of the throttle valve plate from the throttle position sensor; engine coolant temperature; and the oxygen content in the exhaust gases via a sensor in the exhaust manifold. Battery voltage is also monitored by the ECU.

3. Using the information gathered from the various sensors, the ECU sends out signals to control the system actuators. The actuators include the fuel injector, the idle air control stepper motor, the fuel pump relay and the ignition control unit.

4. The ECU also has a diagnostic function which can be used in conjunction with special Vauxhall test equipment for fault diagnosis.

With the exception of basic checks to ensure that all relevant wiring and hoses are in good condition and securely connected, fault diagnosis should be entrusted to a Vauxhall dealer.

5. The system incorporates a three-way catalytic converter to reduce exhaust gas pollutants, and a closed-loop fuel mixture control (by means of the exhaust gas oxygen sensor) is used. The mixture control remains in an open-loop mode (using pre-programmed values stored in the ECU memory) until the exhaust gas oxygen sensor reaches its normal operating temperature.

1.8 litre models

Early (18E engine) models

6. A Bosch LE Jetronic fuel injection system is fitted to all early 1.8 litre models fitted with the 18E engine.

7. By means of electronic control, the fuel injection system supplies the precise amount of fuel for optimum engine performance with minimum exhaust emission levels. This is achieved by continuously monitoring the engine using various sensors, whose data is input to an electronic control unit in the form of electrical signals. Based on this constantlychanging data, the control unit determines the fuel necessary to suit all engine speed and load conditions, which is then injected directly into the inlet manifold.

8. The main components of the system are:

  1. Control unit - the signals delivered by the various sensors are processed in the control unit, and from these signals, the appropriate control impulses for the fuel injectors are generated Additional circuitry within the control unit operates an overrun fuel cut-off to reduce fuel consumption, and a cold start booster for cold starting fuel enrichment.
  2. Control relay - this comprises an electronic timing element and a switch relay, which cuts off the fuel supply immediately after the engine stops.
  3. Airflow sensor - the amount of air drawn in by the engine is measured by the airflow sensor to determine the engine load condition. This is achieved by using a flap valve attached to a spindle, which is free to pivot within the airflow sensor bore, and is deflected by the passage of intake air. Attached to the flap valve spindle is a potentiometer, which transforms the angular position of the flap valve into a voltage, which is then sent to the control unit. Airflow passing through the sensor is one of the main variables used by the control unit to determine the precise fuel requirement for the engine at any given time.
  4. Fuel injectors - each fuel injector consists of a solenoid-operated needle valve, which opens under commands from the control unit. Fuel from the fuel distribution pipe is then delivered through the injector nozzle into the inlet manifold. All four fuel injectors operate simultaneously; once for each turn of the crankshaft regardless of inlet valve position. Therefore, each injector will operate once with the inlet valve closed, and once with it open, for each cycle of the engine. The fuel injectors always open at the same time relative to crankshaft position, but the length of time in which they stay open, eg the injector duration, is governed by other variables, and is determined by the control unit. For a given volume of air passing through the airflow sensor, the control unit can enrich the air/fuel mixture ratio by increasing the injector duration, or weaken it by decreasing the duration.
  5. Fuel pump - the fuel pump is an electric self-priming roller cell unit, located at the rear of the car. Fuel from the tank is delivered by the pump, at a predetermined pressure, through the fuel filter to the fuel distribution pipe. From the fuel distribution pipe, the fuel is supplied to the four fuel injectors the excess being returned to the fuel tank via the fuel pressure regulator. A greater volume of fuel is circulated through the system than will be needed, even under the most extreme operating conditions, and this continual flow ensures that a low fuel temperature is maintained. This reduces the possibility of vapour lock, and ensures good hot starting characteristics.
  6. Fuel pressure regulator - the fuel pressure regulator Is fitted to the fuel distribution pipe, and controls the operating pressure in the fuel system. The unit consists of a metal housing, divided into two chambers by a diaphragm. Fuel from the fuel distribution pipe fills one chamber of the regulator, whilst the other chamber contains a compression spring, and is subject to inlet manifold vacuum via a hose connected to the manifold, downstream of the throttle valve. A valve attached to the diaphragm opens a fuel return port in the fuel chamber of the regulator as the diaphragm deflects.

    When the fuel pressure in the regulator exceeds a certain value, the diaphragm is deflected, and fuel returns to the tank through the now open return port. This also occurs when the port is opened by the deflection of the diaphragm under the influence of manifold vacuum. Therefore, as manifold vacuum increases, the regulated fuel pressure is reduced in direct proportion.

  7. Throttle valve switch - the throttle valve switch is attached to the throttle spindle on the throttle valve housing. As the throttle spindle turns in response to movement of the accelerator pedal, contacts within the switch are closed at the two extremes of shaft movement. One contact closes in the idle position, and one in the full-throttle position. These signals are then processed by the control unit to determine throttle valve position.
  8. Auxiliary air valve - this device comprises a large-bore air channel, connected by hoses to the throttle housing and inlet manifold, and allowing intake air to bypass the throttle valve. In the centre of the air channel is a blocking plate attached to a bi-metal strip. When the engine is cold, the blocking plate is withdrawn from the air channel, allowing air to pass through the valve. As the engine warms up, a current is supplied to the valve, heating the bi-metal strip and causing the blocking plate to begin closing the air channel until, as engine temperature increases, the channel is closed completely. The additional air passing through the valve is measured by the airflow sensor, which compensates by increasing the injector duration to provide additional fuel. Therefore, the engine receives a greater air/fuel mixture during cold driveaway and warm-up conditions.
  9. Temperature sensors - information on engine (coolant) temperature and intake air temperatures are measured by sensors, one located in the coolant jacket and the other in the intake air stream. The sensors consist of resistors whose resistance decreases as temperature increases. The change in electrical resistance of the sensors is measured by the control unit, and this information is used to modify injector duration accordingly.

Later (1987 onwards) 1.8 litre models

9. A Bosch L3 Jetronic fuel injection system is fitted to all later 1.8 litre models fitted with the 18SE engine.

10.The system is based on the LE system used previously, but it has a digital control system, rather than the analogue system used on the LE type. The L3 system control unit is housed within the engine compartment as part of the airflow sensor assembly, and the system wiring layout differs to suit.

2.0 litre models

11. The Motronic systems fitted to 2.0 litre models control the fuel injection and ignition systems as an integrated package. This has considerable advantages in terms of efficiency, performance and reduction of exhaust emissions.

12. Idle speed is regulated by the opening and closing of an electrically-operated valve which allows air to bypass the throttle butterfly. No manual adjustment is possible.

13. Ignition timing is advanced and retarded electronically in response to engine speed and load, engine temperature and inducted air temperature. Engine speed information comes from an inductive pulse sensor on the side of the cylinder block. The sensor is mounted close to the toothed lockwasher attached to the crankshaft No 1 counterweight. The passage of each lockwasher tooth produces an electrical pulse in the sensor. This signal is transmitted to the control unit.

14. The system fitted to 8-valve models before 1990 is known as Motronic ML4.1. The fuel injection side is very similar to the LE/L3 Jetronic systems fitted to 1.8 models. The control unit is located behind the trim panel in the driver's footwell.

15.1990 8-valve models are fitted with a system known as Motronic M1.5. The main difference is in the control unit, which triggers the injectors in pairs instead of all together as previously. There are also minor differences in the fixings of the fuel pressure regulator and the fuel injector rail. The fuel pump is now immersed in the tank instead of being fitted alongside.

16. The system fitted to 16-valve models is known as Motronic M2.5. The most significant difference from the other Motronic systems is in the way that intake air is measured. Where the other systems measure air volume by means of a flap, the M2.5 system measures air mass by its cooling effect on a hot wire.

The M2.5 system also incorporates knock control, whereby detonation (pre-ignition or pinking) is sensed and causes the ignition timing to be retarded.

17. Injection on the M2.5 system is fully sequential. Each injector is individually controlled to deliver fuel at the optimum moment in the induction process. The ignition distributor carries a Hall Effect sensor which sends the control unit a cylinder recognition signal.

18. On all systems, the control unit incorporates self-testing and fault detection features. Fault codes are stored in the unit, but these are only accessible to Vauxhall dealers or other specialists with the necessary test equipment.

19. If a fault is detected by the control unit, a 'limp home' program comes into operation by means of which an average value is substituted for the normal output of a defective or disconnected sensor. In this case the vehicle is still driveable, albeit with reduced performance and efficiency. A warning light on the instrument panel, carrying an outline of an engine and a lightning symbol, warns the driver that a fault has occurred.

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