Audi 80/Avant (B4)

since 1991-1995 of release

Repair and car operation

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
- Injection system
   + 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 a 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 electrosystem
+ ignition System
+ Lighting
+ 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 number of air because both butterfly valves in this case 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 should be mixed to fuel in precisely certain proportion. For definition of a proportion of fuel/air the system of injection of MPI uses mass of inlet air. The air flowmeter thus is to the MPI control unit a source of information of inlet weight of air. Comparable size of system of injection of MPFI – information on pressure in a final collector and about temperature.

The control unit can give now the correct impulses for opening and closing of vpryskny nozzles. 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. «The injection capacity» nozzles remains thus to a constant. Reduction of quantity occurs by means of reduction «injection time».


The enriched is necessary for start of the cold engine – that is with the raised content of fuel – a mix because fuels much of 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. Therefore, it is necessary to enrich a mix.

The program of start of the cold engine cares of it, written down in memory of the control unit. 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 any time the enriched mix as a fuel quantity still continues to be condensed in admission system 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 raised internal friction at the cold engine. Therefore the bigger effort (richer a mix) to support necessary frequency of rotation is necessary. Receipt of the enriched mix provides already mentioned valve of stabilization of frequency of rotation of a shaft of the engine in an idling mode.


At the closed butterfly valve (the released pedal of an accelerator) 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 a mix for an idling mode. By the way, the mix for a mode of idling is richer in comparison with a usual mix that becomes in order that the engine worked exactly, without ignition differences. During what moment it is necessary to make enrichment for an idling mix, the control unit learns from a butterfly valve potentiometer. How many air will pass through байпас (and, thereby, and the range of frequency of rotation in an idling mode), defines the valve of stabilization 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 fuel consumption.


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

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 a mode of full loading).

Fuel interruption of supply in a mode of compulsory idling (movement nakaty)

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

Restriction of frequency of rotation

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