Audi 80/Avant (B4)

since 1991-1995 release

Repair and operation of the car

Audi 80/Avant
+ Technical specification
+ Engines
+ 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 of Mono-Motronic
   + System of injection of Digifant
   + System of injection of KE-III-Jetronic
   - Systems of injection of MPI and MPFI
      Operating procedure
      Lambda regulation
      Malfunctions and independent diagnostics
      Independent repair
      Visual check
      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
+ Coupling
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Anti-blocking system of brakes
+ Wheels and tires
+ Body electrical system
+ System of ignition
+ Lighting
+ Signalling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ body Elements
+ Search of malfunctions
+ Specifications

Operating procedure

Interaction of components

The 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 number of air because in this case both butterfly valves are completely open. Respectively at the closed or partially open provision of butterfly valves the amount/weight of air is less. For a neat job of the engine inlet air has to be mixed to fuel in precisely certain proportion. For definition of a proportion of fuel/air the system of injection of MPI uses the mass of inlet air. The air flowmeter thus is the MPI control unit a source of information of inlet mass of air. The comparable size of system of injection of MPFI – information on pressure in a final collector and about temperature.

The control unit can give the correct impulses for opening and closing of vpryskny nozzles now. More long opening is necessary if there is a need for a large amount of fuel, – it is enough short-term opening if only a small amount of fuel is necessary. "Injection power" of nozzles remains thus to a constant. Reduction of quantity happens by means of reduction of "injection time".


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

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

Phase of warming up of the engine

After start during some time the enriched mix as a fuel quantity still continues to be condensed in system of an admission is also necessary for the engine. For this purpose there is "a poststarting enrichment". During certain time depending on temperature the bigger amount of fuel arrives. The control unit receives necessary information on engine temperature from the sensor of temperature of cooling liquid.

Rather viscous engine oil causes the increased internal friction at the cold engine. Therefore the bigger effort (richer mix) to support the necessary frequency of rotation is necessary. Intake of the enriched mix provides already mentioned valve of stabilization of frequency of rotation of a shaft of the engine in the idling mode.


At the closed butterfly valve (the released accelerator pedal) a small amount of air passes through the channel by a butterfly valve. The amount of this air is defined by a flowmeter of air or the sensor of pressure and is supplemented with necessary amount of fuel for receiving mix for the idling mode. By the way, mix for the mode of idling is richer in comparison with usual mix that becomes in order that the engine worked exactly, without ignition differences. At what moment it is necessary to make enrichment for idling mix, the control unit learns from a potentiometer of a butterfly valve. How many air will pass through baypas (and, thereby, and rotation frequency range in the idling mode), defines the valve of stabilization of frequency of rotation of a shaft of the engine in the idling mode.

Partial loading

In the mode of partial loading the engine receives normal portions of fuel. Thus the maximum attention is paid to perhaps more economic fuel consumption.


If the pedal of an accelerator is suddenly squeezed out, it causes enrichment of mix for acceleration in case increase of amount/weight of inlet air in a second exceeds a certain size. Also the signal of dispersal arrives from a potentiometer of a butterfly valve. If the engine still cold, dispersal requires still bigger amount of fuel. The control unit therefore distinguishes the corresponding impulse of a flowmeter of air or the sensor of pressure and a potentiometer of a butterfly valve as a signal of dispersal and increases fuel supply.

Full loading

The potentiometer of a butterfly valve signals the control unit that the driver completely squeezed out an accelerator pedal. For achievement of the maximum loading the engine receives the enriched mix (enrichment for the mode of full loading).

Interruption in supply of fuel in the mode of compulsory idling (the movement by a setup)

If the car goes downhill and thus the accelerator pedal is not squeezed out, the engine does not need fuel supply. The car moves itself under the weight or by inertia. On the high frequency of rotation and situation of the closed butterfly valve (by means of a potentiometer of a butterfly valve) the control unit distinguishes the mode of compulsory idling (the movement by a setup) and can switch in the provision of "economy of fuel".

Restriction of frequency of rotation

The system of injection compares the operating rotation frequency with maximum, making 6500 rpm, and at excess it simply stops fuel supply (see also head Dvigateli).