AUDI 80 vehicles with a 2.8-liter six-cylinder engine have an MPI multipoint injection system. The abbreviation MPI is derived from the first letters of the English name for this Multi Point Injection system. A distinctive feature of this system is the presence of an air mass meter installed in the air inlet hose.
Vehicles with the 2.6L six-cylinder engine also have the MPFI multipoint injection system, which is identical to the MPI. The main difference between the MPFI system and the MPI system is the way in which the volume or mass of intake air is measured. The MPI system is equipped, as indicated, with an air mass meter, and the MPFI instead has an intake manifold pressure sensor, which is installed in the electronic control unit and connected by a hose to the intake manifold. In addition, the MPFI has an intake air temperature sensor in the intake manifold. The abbreviation MPFI is also made up of the first letters of the English name for this Multi Point Fuel Injection system.
The MPI/MPFI multi-port fuel injection system is quite large. Its electronic unit is integrated with the ignition system. The control unit has a self-diagnostic system. This means that all malfunctions that occur during operation are recorded in the memory of the drive. In this case, even short-term malfunctions are fixed. As experience shows, they are the most difficult to detect defects. After every 50 engine starts, an automatic deletion of the fault record is performed, which manifested itself only once and did not recur.
The electronic control unit, based on the degree of load on the engine and its temperature, «highlights» appropriate amount of fuel. To this end, the control unit varies the duration of the opening of the nozzles. The pressure in the fuel system is maintained at an approximately constant level and for this reason the amount of fuel injected can only be controlled by the duration of the opening of the injectors. The control unit receives the relevant information from a sufficiently large number of sensors or measuring instruments.
- A) The intake air mass meter on vehicles with a 2.8-liter six-cylinder engine reports the amount of air that has been taken in.
- b) The intake air temperature sensor, together with the intake manifold pressure sensor on vehicles with a 2.6L six-cylinder engine, also reports the amount of air that has entered.
- V) The coolant temperature sensor provides information about the current engine temperature.
- G) The throttle position potentiometer provides information about the load on the engine.
- d) The engine speed sensor provides information to the ignition and fuel injection systems.
- and) The ignition timing sensor reports the position of the crankshaft. In this way, the electronic control unit learns which cylinder should be ignited and which should be injected.
- h) The starter terminal 50 is the source of engine start information.
In addition, the control unit receives information from the knock sensors, from the gearbox sensors and even from the air conditioner.
On the inlet channel of each cylinder there is one nozzle, which injects the amount of fuel required at the moment, providing at the same time its smallest atomization.
The injectors are electromagnetically controlled, which raises the injector nozzle needle by about 0.1 mm, allowing fuel to escape. The injectors fire at the moment of the intake stroke and therefore the injected fuel, due to lack of time, does not have time to settle on the walls of the intake cable. This means that the system does not allow fuel losses.
The fuel distribution line is designed to evenly supply all six injectors with fuel. In addition, it functions as a fuel accumulator and does not allow fluctuations in fuel pressure.
The fuel pressure reducing valve is located on the fuel distribution line on the right side and is designed to maintain the fuel pressure at a constant level. This is achieved by diverting part of the fuel back to the fuel tank. A low air pressure hose is connected to the pressure reducing valve and the valve thus receives information about the load on the engine. At full load, the valve increases the pressure in the fuel distribution line, providing an increase in the amount of fuel injected.
The intake air mass meter on the MP1 multipoint fuel injection system has a glow filament located in the air path. The passing air cools the thread to some extent. Depending on the degree of cooling, additional voltage is applied to the filament to keep the filament glow constant. Such fluctuations in the filament temperature change the electrical resistance of the filament, which in turn controls the electronic control unit.
As for the MPFI multipoint fuel injection system, it has an intake manifold pressure sensor. This sensor, located in the electronic control unit, is connected to the intake manifold with a thin hose. The pressure in the intake manifold is very important information for the control unit, on the basis of which the load on the engine is recognized.
The intake air temperature sensor is screwed into the intake port of the third cylinder (rear right). The information from this sensor, together with the information from the intake manifold pressure sensor, serves as an electronic sensor to determine engine load. At high intake air temperature (in this case the air density is low) there is a need to reduce the duration of fuel injection, and the ignition timing should be shifted to a later one.
Two throttle valves are installed in the pipe from which the intake air enters the intake manifold. The smaller of these shutters is connected by a cable «gas» with accelerator pedal. Until the accelerator pedal reaches the position «Full throttle», this flap regulates intake air metering. And only when the accelerator pedal is sufficiently depressed, the corresponding rod opens the second flap of a larger diameter.
The throttle valve angle potentiometer is driven by the throttle valve shaft. The potentiometer registers the current throttle position and reports it to the electronic control unit in the form of a voltage signal. The throttle position is needed by the control unit to control idle, select the ignition timing and duration of fuel injection.
The very name of the idle speed stabilization valve speaks of its purpose. The valve is only an executive body. It receives the appropriate order from the electronic control unit, which constantly compares the current engine speed with the nominal one and, if necessary, causes the idle speed stabilization valve to open or close. As a result of opening or closing the valve, an increase or decrease in the opening through which air enters bypassing the throttle valve occurs. Intake air mass flow meter «believes», that the air volume has increased as a result of the throttle opening and provides a corresponding increase in injected fuel. The MPI system has a stepless idle stabilization valve, MPFI - a valve with an actuator motor.
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