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
      Operating procedure
      Malfunctions and independent diagnostics
      Independent repair
      Visual check
      Check of separate elements
      Removal of vpryskny nozzles
      Check of the mode of idling and analysis of exhaust gases
      List of malfunctions
   + System of injection of KE-III-Jetronic
   + Systems of injection of MPI and MPFI
+ 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

System of injection of Digifant

On this illustration the system of injection of Digifant with its components is schematically presented. The way of air is shown by white shooters, supply with fuel is presented in the red color.

1 – fuel tank;
2 – fuel filter;
3 – pressure regulator;
4 – fuel distributor;
5 – nozzle;

6 – inlet collector;
7 – air flowmeter;
8 – idling stabilization valve;
9 – fuel pump.

Multipoint injection

The system of injection in which each cylinder has own vpryskny nozzle, than that in which injection is carried out only by one central nozzle is suitable for perhaps more exact distribution of mix of fuel/air better. Therefore the 85 Kw engine is supplied with the multipoint (distributed) system of injection. It is about electronically the operated system with the programmed characteristic of injection, with the operated system of ignition, with the ignition moment regulated on a detonation, with the integrated stabilization of frequency of rotation in the mode of idling and with interruption in supply of fuel in the mode of compulsory idling.

To whom the name of this system of injection is reminded by the word "Elefant" (elephant), that is near from truth at all. Electronics engineers of Volkswagen and Audi took this name from "a white elephant" (weiber Elefant) – among programmers so call Jacks of all trades. New word formation – Digitaler Elefant.

Basic elements

Control unit

The control unit receives via the multicontact plug the following types of information from:

  • Starter from the plug 50 – about the beginning and the end of process of start.
  • Potentiometer of a butterfly valve – about the current provision of a butterfly valve.
  • The Hall sensor in the ignition distributor – about the frequency of rotation of the engine.
  • Lambda probe in catalytic converter – about the content of residual oxygen in the fulfilled gases.
  • Potentiometer in an air flowmeter – about position of the retaining valve (amount of the let-in air).
  • The sensor of temperature of inlet air in an air flowmeter.
  • The sensor of temperature of cooling liquid in a cooling system branch pipe.
  • The sensor of detonation combustion on the block of cylinders for "detonation" combustion, see also head System of ignition.

On the basis of information on the frequency of rotation and loading the control unit counts duration of opening of electromagnetic vpryskny nozzles and by that injectable amount of fuel. For this purpose characteristics of injection and in addition the characteristic of ignition are at the disposal of the control unit. These characteristics represent collection of data for various situations at operation of the engine and the corresponding amounts of fuel, and also the ignition moments. These indicators the control unit can change after receipt of so-called adjustment signals (for example temperatures of inlet air and cooling liquid).

Butterfly valve

Two butterfly valves are in a branch pipe in an inlet collector. Smaller from these gates it is connected by a cable of the drive of "gas" with a pedal in salon. It doses a stream of inlet air in the engine. If the pedal of an accelerator is squeezed out more strongly, draft opens the second, big gate, in the provision of full "gas" both gates are open.

Potentiometer of a butterfly valve

The potentiometer of a butterfly valve covers the provision of a butterfly valve from "idling" at present (the butterfly valve is closed) to "full loading" (the butterfly valve is completely open). On the basis of its information idling stabilization, interruption in supply of fuel in the mode of compulsory idling or enrichment of gas mixture at full opening of a butterfly valve is activated.

Pressure regulator

It is located in front of the distributor of fuel and regulates pressure of supply of fuel to vpryskny nozzles. For this purpose he receives information on a condition of depression in an inlet collector. At the closed butterfly valve and high depression it keeps lower pressure in the idling mode. At decrease in depression at bigger loading of the engine the regulator of pressure increases fuel supply pressure. The fuel pump gives fuel with more high working pressure, but thanks to the regulator of pressure of plums of gasoline back in a fuel tank respectively increases or, if necessary, decreases.


At each turn of a cranked shaft they inject gasoline in vpryskny the channel in front of the inlet valve of the corresponding cylinder – duration of this process defines the control unit. The corresponding cylinder receives one portion for emergency, and the second at the open inlet valve directly in the combustion chamber.

The sensor of temperature of the arriving air

It is located sideways in a flowmeter of air and thus can precisely determine temperature of the arriving air. Temperature of inlet air gets to the control unit in the form of resistance indicator. This indicator is necessary for an optimum dosage of fuel.

Sensor of temperature of cooling liquid

Temperature of cooling liquid is necessary for management of many functions of injection: enrichment of starting mix, poststarting enrichment (on all range of temperatures), enrichment at acceleration and shutdown of supply of fuel in the mode of compulsory idling (the movement by a setup). Information on temperature of cooling liquid comes to the control unit also in the form of resistance indicator. The control unit counts the necessary duration of injection which at the engine warmed up to the working temperature is in range between two and eight milliseconds. This indicator can increase to 70% if temperature of cooling liquid reaches –25 °C.

Air flowmeter

The air, necessary for combustion arriving from the air filter, more or less (depending on the let-in quantity) wrings out a valvate lock in an air flowmeter aside, thus the attenuation valve connected with a valvate lock prevents fluctuations of a valvate lock. The potentiometer sends to the control unit depending on the provision of a valvate lock a signal in the form of tension: a high voltage at full opening and a large amount of air, small tension at small opening.

Starting fuel valve

This vpryskny nozzle with the electromagnetic drive injects in vpryskny the collector additional amount of fuel during 1 — 4 with depending on engine temperature at start. Duration of injection defines the control unit of system of injection of Digifant.

Idling stabilization valve

In a warming up phase, at full turn of the amplifier of the steering mechanism, at the working conditioner or at the included step of an automatic transmission this valve frees the additional air canal, bypassing thereby a butterfly valve.

The strengthened air exchange in the direction of an inlet collector at the same time leads to the strengthened fuel supply. The increased friction in the engine in a cold state or higher load of the engine caused by the power steering pump spending energy, the conditioner compressor, and also an automatic transmission is so counterbalanced.

The valve of stabilization of frequency of rotation of a shaft of the engine in the mode of idling is used and in the mode of compulsory idling. It allows to arrive to amount of air, necessary for the movement, at the closed butterfly valve.