Audi 80/Avant (B4)
since 1991-1995 release
Repair and operation of the car
+ Technical specification
+ System of production of the fulfilled gases
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and airintaking channels
- System of injection
+ System of injection Mono-Motronic
+ System of injection Digifant
+ System of injection KE-III-Jetronic
- Systems of injection of MPI and MPFI
Malfunctions and independent diagnostics
Check of separate elements
Removal of elements
Hummock drive of "gas"
Check of the mode of idling and analysis of exhaust gases
List of malfunctions
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Anti-blocking system of brakes
+ Wheels and tires
+ Body electrical system
+ System of ignition
+ Signaling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ Body elements
+ Search of malfunctions
Systems of injection of MPI and MPFI
The scheme in detail shows system of ignition and injection on the example of the MPFI system with pressure sensor in an inlet collector. On the left side the sensors and sensors influencing behavior of the control unit are located. On the right components of systems of ignition and injection to which the control unit sends the teams are presented.
System of injection MPI/MPFI with т.з. fuel supply
Electronics helps to constrain a few "appetites" of the engine even of the most powerful Audi 80 version. However, at more than probable fuel consumption over 12 l on 100 km it is not always possible to be quite convinced that this good intention is carried out. But nevertheless follows that high engine capacity justifies this extra charge for high high-speed qualities of the car.
The 2,8-liter engine is supplied with system of injection with the designation MPI. The English words Multi Point Injection – in Russian "multipoint injection" are behind this reduction. (The distinctive sign of system of injection of MPI is a flowmeter of air in an air inlet sleeve behind on the right in a motor compartment).
For the best understanding of the general functioning of this system of injection it is necessary to get acquainted with separate problems of components at first.
Between arriving (from various sensors) the control unit is information and vpryskny nozzles. It allows the engine, depending on the operating conditions of loading and temperature, to receive precisely certain amount of fuel. For achievement of it the control unit varies duration of opening of nozzles with the electromagnetic drive. As pressure in a fuel supply system constantly remains almost invariable, the amount of injectable fuel can be regulated only by means of change of duration of injection. From where the control unit obtains information according to which it establishes this duration of injection? Various sensors are responsible for it:
In an inlet collector of each cylinder of the engine there is about one vpryskny nozzle. They bring to the corresponding cylinder amount of fuel necessary at present and at the same time provide thin dispersion of gasoline.
It is intended for uniform supply with fuel of all vpryskny nozzles. Besides, the distributor of fuel operates and as the fuel store, thereby preventing pressure differences. The U-shaped form of a pipe allowing a fuel supply to all six nozzles is very interesting.
Fuel supply pressure regulator
It is located behind on the right on the distributor of fuel and has to – according to the name – to support the constant level of pressure in the fuel distributor. It is carried out by means of more or less strong outflow of fuel back in the fuel tank on the drain highway. If on the drain highway more fuel leaves, then pressure decreases; if it is less – pressure increases.
Fuel pump and relay
In more detail you learn about the electromagnetic fuel pump, the relay of the fuel pump and other MPI/MPFI relays in the head the Fuel tank and the fuel pump.
On the way of a stream of the soaked-up air there is a wire which is warmed up electrically. Depending on the let-in quantity the air stream changes that leads to more or less strong cooling of the mentioned wire. Change of temperature leads to change of electric resistance of a wire which is measured by the control unit.
Pressure sensor in an inlet collector
Pressure sensor in an inlet collector is in the MPFI control unit. Connection between an inlet collector and the sensor represents a thin hose. Pressure in an inlet collector is for the control unit of information front view for calculation of loading of the engine. It influences duration of injection and the moment of ignition.
Sensor of temperature of inlet air
The sensor of temperature of inlet air is screwed in in the inlet canal of the third cylinder (behind on the right). In addition to pressure sensor in an inlet collector it is for the control unit a source to an inofrmation for calculation of load of the engine. At high temperature of inlet air (that is equivalent the low density of air) it is necessary to reduce, for example, duration of injection and to shift the ignition moment aside "later" a little.
Case of throttle knot
Where the stream of the soaked-up air gets to an inlet collector of the engine, in one case there are two butterfly valves. Smaller of gates it is connected by means of the hummock drive to an accelerator pedal. It doses a stream of inlet air in the engine to the provision of half loading. By further pressing an accelerator pedal the lever of draft opens the second, big gate until in the provision of full loading there are no completely open both gates.
Potentiometer of a butterfly valve
The potentiometer of a butterfly valve is put in action by the roller of a butterfly valve. The potentiometer defines the provision of a butterfly valve of time at present and transfers to the control unit this information in the form of electric resistance. The control unit needs this information on loading, for example, for regulation of frequency of rotation in the mode of idling, choice of the characteristic of ignition and calculation of duration of injection.
Valve of stabilization of frequency of idling
As it is already clear according to the name, this valve constantly provides the constant frequency of rotation of a shaft of the engine in the idling mode – all the same whether the engine is cold or heated-up, are included or not powerful consumers of the electric power like the conditioner.
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