Audi 80/Avant (B4)

Since 1991-1995 of release

Repair and car operation

Audi 80/Avant
+ The description
+ Engines
+ System of release of the fulfilled gases
+ Cooling system
+ Fuel tank and the fuel pump
+ The air filter and воздухозаборные channels
- Injection system
   + System of injection Mono-Motronic
   + System of injection Digifant
   + System of injection KE-III-Jetronic
   - Systems of injection MPI and MPFI
      Operating procedure
      Malfunctions and independent diagnostics
      Independent repair
      Visual check
      Check of separate elements
      Removal of elements
      Trosovyj drive of "gas"
      Check of a mode of idling and the analysis of exhaust gases
      The list of malfunctions
+ Coupling
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Antiblocking system of brakes
+ Wheels and tyres
+ Kuzovnaja electrosystem
+ Ignition system
+ Illumination
+ Signalling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ Body elements
+ Search of malfunctions
+ Specifications

Operating procedure

Interaction of components

Pistons rising and falling at the working engine involve air. If you completely squeeze out an accelerator pedal the engine soaks up the greatest possible quantity of air because both in this case are completely open throttle заслонки. Accordingly at the closed or partially open position throttle заслонок the quantity/weight of air is less. For a neat job of the engine inlet air should be mixed to fuel in precisely certain proportion. For definition of a proportion of fuel/air the system of injection MPI uses weight of inlet air. Air flowmeter thus serves the block of management MPI as a source of the information of inlet weight of air. Comparable size of system of injection MPFI – the information on pressure in a final collector and about temperature.

The management block can give now correct impulses for opening and closing впрыскных atomizers. More long opening is necessary, if there is a requirement for a fuel considerable quantity, – it is enough short-term opening, if the fuel small amount is necessary only. «Capacity of injection» atomizers remains thus to a constant. Quantity reduction occurs by means of reduction of "injection time».


For start of the cold engine it is necessary enriched – that is with the raised maintenance of fuel – a mix because many of fuel droplets are condensed on internal walls of system of injection already on a way to combustion chambers, that is do not participate in combustion process. Hence, it is necessary to enrich a mix.

The program of start of the cold engine cares of it, written down in memory of the block of management. During regulation of cold start is a certain number of ignitions – duration of injection of atomizers increases. Duration of injection is influenced by such factors, as temperature of a cooling liquid and frequency of rotation. After certain number of turns the quantity of fuel at cold start gradually is reduced to the normal.

Phase of warming up of the engine

After start during any time the enriched mix as a fuel quantity still continues to be condensed in admission system also is necessary for the engine. For this purpose exists «послестартовое enrichment». During certain time depending on temperature arrives большее quantity of fuel. The management block receives the necessary information on temperature of the engine from the gauge of temperature of a cooling liquid.

Rather viscous engine oil causes the raised internal friction at the cold engine. Therefore it is necessary большее effort (richer a mix) to support necessary frequency of rotation. Receipt обогощенной mixes provides already mentioned valve of stabilisation of frequency of rotation of a shaft of the engine in an idling mode.


At closed throttle заслонке (the released pedal of an accelerator) air small amount passes through the channel by throttle заслонки. The quantity of this air is defined by a flowmeter of air or the gauge of pressure and supplemented with necessary quantity of fuel for reception of a mix for an idling mode. By the way, the mix for an idling mode is richer in comparison with a usual mix that becomes that the engine worked exactly, without ignition differences. During what moment it is necessary to make enrichment for an idling mix, the management block learns from a potentiometer throttle заслонки. How many air will pass through байпас (and, thereby, and the range of frequency of rotation in an idling mode), defines the valve of stabilisation of frequency of rotation of a shaft of the engine in an idling mode.

Partial loading

In a mode of partial loading the engine receives normal portions of fuel. Thus the maximum attention is given probably to more economic expense of fuel.


If the accelerator pedal is suddenly squeezed out, it causes enrichment of a mix for acceleration, in a case if increase of quantity/weight of inlet air in a second exceeds certain size. As the dispersal signal arrives from a potentiometer throttle заслонки. If the engine still cold for dispersal it is necessary still большее quantity of fuel. The management block therefore distinguishes a corresponding impulse of a flowmeter of air or the gauge of pressure and a potentiometer throttle заслонки as a signal of dispersal and increases fuel giving.

Full loading

The potentiometer throttle заслонки signals the management block that the driver has completely squeezed out an accelerator pedal. For achievement of the maximum loading the engine receives the enriched mix (enrichment for a mode of full loading).

Fuel stopping delivery in a mode of compulsory idling (movement накатом)

If the car goes downhill and thus the accelerator pedal the engine does not require fuel giving is not squeezed out. The car moves itself under the weight or by inertia. On high frequency of rotation and position closed throttle заслонки (by means of a potentiometer throttle заслонки) the management block distinguishes a mode of compulsory idling (movement накатом) and can be switched in position of "economy of fuel».

Restriction of frequency of rotation

The injection system compares operating frequency of rotation about the maximum, making 6500 rpm, and at its excess simply stops fuel giving (Engines see also the head).