Audi A4

since 1994 release

Repair and operation of the car



A4 Audi
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and channels of absorption
- System of injection
   - System of injection of Motronic
      The major knots
      So the system of injection of Motronic functions
      Violations in work and self-diagnostics
      The self-help at injection
      Visual control
      Search of malfunctions in separate knots
      Check of idling and exhaust gases
      Check of exhaust gases (AU)
      Cable of a butterfly valve
      The help at malfunctions
   + System of injection of MPI and MPFI
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
+ Electrotechnical equipment
+ System of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ body Details
+ Salon
Search of malfunctions
Technical characteristics





The major knots

Electronic control unit

The control unit in an electronic box via the mnogoshtyrkovy socket receives information:

  • starter, the plug 50 began also completion of process of start-up;
  • potentiometer of a butterfly valve, its situation at the moment;
  • the sensor of the Hall of system of ignition for adjustment of number of turns of the engine;
  • lambda probe in the catalytic converter for measurement of the content of residual oxygen in exhaust gases;
  • the measuring instrument of a stream of the soaked-up air;
  • the sensor of temperature of the soaked-up air (only in the 110 kW turbo engine);
  • the sensor of temperature of cooling liquid in a tube of supply of cooling liquid behind a head of the block of cylinders;
  • sensor of a detonation of I on the block engine at "detonation" combustion;
  • sensor of a detonation of II (only in engines with a working volume of 1,8 l) also on the engine block for exact localization of detonation combustion.

On the basis of information on number of turns and pressure in an inlet collector the control unit counts duration of opening of the injectors which are put in action in the electromagnetic way, and, respectively, amount of injectable fuel. For this purpose the characteristics of the engine representing collection of data on all imaginable situations of the engine about amount of fuel, necessary for each situation, and the corresponding moment of ignition are made to the control unit available. The control unit can vary still characteristics after receipt of the so-called correcting signals (for example, temperature of the soaked-up air and cooling liquid).

Control unit of a butterfly valve

The control unit (2) systems of ignition/injection is in an electronic box at the left behind in a motive compartment (in the so-called moistening tank). In an arm (1) near the control unit there is height sensor place for the turbo engine.


The control unit of a butterfly valve in the turbo engine with a working volume of 1,8 l: 1 – lever of a butterfly valve; 2 – junction point of power supply of the control unit (3) of a butterfly valve; 4 – butterfly valve.


The control unit of a butterfly valve in the engine with a working volume of 1,6 l in principle is identical to the engine block with a working volume of 1,8 l, though assembly situation at it another. Are designated by figures: 1 – a junction point to power supply; 2 – lever of a butterfly valve.

In the so-called control unit of a butterfly valve three separate knots known on other systems of injection as functional blocks are integrated.

Butterfly valve. It is connected by a cable with a pedal in salon and doses a stream of fresh air in the engine. The more the gas pedal is pressed, the butterfly valve opens more strongly, at full gas it is open completely.

Potentiometer of a butterfly valve. The potentiometer of a butterfly valve defines the provision of a butterfly valve on given the moment in the range from idling (the butterfly valve is closed) to full gas (the butterfly valve is open completely). On the basis of its information the idling stabilization valve which is also integrated in a branch pipe of a butterfly valve becomes more active, there is a shutdown of draft or enrichment of mix at full loading.

Idling stabilization valve. It lets in the dosed additional amount of air canals of absorption behind a butterfly valve at a stage of warming up of the engine, at full turn of a servoupravleniye, at the working climatic installation or the established step of automatic transfer. The raised air stream in the direction of the soaking-up pipeline is distinguished by the measuring instrument of a stream of fresh air and as a result causes the increased fuel supply. Thus, there is a decrease in the increased friction in not heated-up engine or at the raised load of the engine at the expense of a servonasos, the compressor of climatic installation or automatic transfer which take away power from the engine.

Pressure regulator

The regulator of pressure (1) fuel is connected to a branch pipe of a butterfly valve by means of a vacuum hose (2). It regulates pressure in system by increase or decrease of recirculation of fuel.

It is in the distributor of fuel and regulates its pressure upon injectors. For this purpose information on level of the lowered pressure is transferred to it in an inlet collector. Idling at the closed butterfly valve and very low pressure it holds lower pressure. With pressure drop at the raised load of the engine the regulator of pressure increases fuel pressure. The fuel pump creates much more high operational pressure, but by means of pressure regulator return of gasoline to a fuel tank respectively increases or decreases.

Injection valves

Valves of injection (4–7) settle down in the direction of travel on the left side of a head of the block of cylinders in an inlet collector. Further are designated by figures: 1 – fuel pressure regulator; 2 – the giving fuel pipe; 3 – distributive tube of fuel.


On this model in a section it is visible that each valve of injection (3) makes injection in the soaking-up pipe (4). Fuel arrives to it from a distributive tube (1), signals for injection go through cable connection (2) to the control unit.

At each turn of the crankshaft they inject gasoline into the canal of absorption in front of the inlet valve of the corresponding cylinder – duration is defined by the control unit.

The sensor of temperature of the soaked-up air

At the 110 kW turbo engine he is in an airintaking hose and can precisely take air temperature, served by a turbocompressor. Information on temperature comes to the control unit in the form of resistance size. It is used for an optimum dosage of fuel. The hot turbocompressor depending on a working condition strongly heats the soaked-up air.

Sensor of temperature of cooling liquid

Temperature of cooling liquid is used at management of several functions of injection: at enrichment of fuel and air mix during start of the cold engine, poststarting enrichment (on all range of temperatures), at enrichment during accelerations and draft shutdown. Information on temperature of cooling liquid is transferred to the control unit also in the form of resistance size. He counts the correct time of injection which in the heated-up engine makes from 2 to 8 ms. This size can increase almost for 70% when temperature goes down to the Arctic level of -25 °C.

Measuring instrument of a stream of fresh air

In a stream of the soaked-up air there is an electroconductive plate which is warmed up in the electroway. Depending on amount of the soaked-up air its stream which cools a plate stronger or more weakly changes. Change of temperature causes change of electric resistance of the conductor. This measured size is used by the control unit.

Behind on the right in a motive compartment of the naturally aspirated engine with a working volume of 1,6 and 1,8 l there is a measuring instrument of a stream of fresh air (1), priflantsovanny to the case of the air filter. The figure "2" showed the connection socket. In the turbo engine with a working volume of 1,8 l the measuring instrument of a stream of fresh air settles down inside in the case of the air filter.