Audi A4

Since 1994 of release

Repair and car operation



Audi А4
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ Exhaust system
+ Cooling system
+ Fuel tank and the fuel pump
+ The air filter and channels всасывания
- Injection system
   + System of injection Motronic
   - System of injection MPI and MPFI
      Additional functions
      Knots of system of injection
      Functioning
      Adjustment by means of a ljambda-probe
      Infringements in work and self-diagnostics
      The self-help
      The visual control
      Check of knots
      Dismantle of separate details
      Cable throttle заслонки
      Inlet collector
      Idling adjustment
      Check of the fulfilled gases
      The help at malfunctions
+ Coupling
+ Transmission and the main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tyres
+ The electrotechnical equipment
+ Ignition system
+ Illumination
+ The alarm equipment
+ Tools and devices
+ Heating and ventilation
+ Body details
+ Salon
Search of malfunctions
Technical characteristics



Knots of system of injection

That it is better to understand functioning of system of injection as a whole, in the beginning it is important to learn about problems of its separate knots.

1 — the Gauge of number of turns of the engine
2 — the Gauge of the moment of ignition
3 — the Hall Gauge
4 — the Gauge of temperature of a cooling liquid
5 — the Gauge of temperature of soaked up air
6 — the Potentiometer throttle заслонки and the switch of a mode of idling
7 — the Sensor control of a detonation I
8 — the Sensor control of a detonation II
9 — the Ljambda-probe I
10 — the Ljambda-probe II
11 — injection Valves
12 — the Target cascade of capacity
13 — Coils of double ignition
14 — the Valve of stabilisation of idling
15 — the Electromagnetic valve of system of the coal filter
16 — the Block of management of heating of ljambda-probes
17 — the Relay of the fuel pump

This scheme illustrates the electric party of system of ignition/injection, in this case on example MPFI with the gauge of pressure of air in an inlet collector. On a left-hand side gauges and sensor controls which influence behaviour of the block of management take places. On the right those knots of ignition and injection to which the management block sends the signals are represented.

The fuel party of system of ignition/injection MPI/MPFI

1 – a regulator of pressure of fuel;
2 – a distributive tube of fuel;

3 – the injection valve.


The block of management (2) system of ignition/injection MPI/MPFI is in an electronic box at the left behind in an impellent compartment (in the so-called humidifying tank). In an arm near to the management block here in the engine with working volume 2,6 l take places the relay (1) heatings of ljambda-probes.

At the left: injection valves (1, 2 and 3) in the six-cylinder engine are located by groups on three on the right and to the left of the central inlet collector.

On the right: behind on the right in an impellent compartment there is a measuring instrument of a stream of fresh air (1), in the engine with working volume 2,8 l прифланцованный to the case of the air filter. Figure "2" designates a connection socket.

The management block

Between the entering information (from various gauges) and injection valves there is an electronic block of management. Depending on existing conditions of loading and temperature it directs absolutely certain quantity of fuel to the engine. With that end in view the management block varies duration of opening of valves of injection operated an electromagnetic way. The quantity of injected fuel can change only at the expense of duration of injection. The information for definition of duration of injection arrives in the block of management from various knots, it:

  • Only in the engine of 2,8 l with MPI: a measuring instrument of a stream of fresh air; from it the information on quantity of soaked up air arrives.
  • Only in the engine 2,6 with MPFI: the gauge of temperature of soaked up air; in a combination to the gauge of pressure of air in an inlet collector (in the management block) it gives comparative size of soaked up/oh quantity/weight of air.
  • The gauge of temperature of a cooling liquid; it delivers comparative size of temperature of the engine.
  • Potentiometer throttle заслонки; from it the information on loading on the engine arrives.
  • The gauge of number of turns; it transmits a signal about number of turns коленвала.
  • The signal about engine start arrives from the plug 50 locks of ignition (starter).
  • Ljambda-probes send a signal about correctness of structure of a toplivno-air mix.
  • Other sizes influencing, arrive from: sensor controls of a detonation, a transmission, a speedometer and if is, from climatic installation.

Injection valves

In the channel всасывания each cylinder of the engine takes places on one valve of injection. It submits quantity of fuel necessary at present to each cylinder and simultaneously provides thin dispersion of gasoline.

Valves are put in action in the electromagnetic way. Thus dosing out needle rises in the saddle approximately on 0,1 mm – fuel can flow.

Distributive tube of fuel

It serves for uniform giving of fuel to all valves of injection. Besides, the distributive tube functions as a collector and thanks to it does not suppose pressure fluctuations. The tube form is interesting кольцевидная, allowing to submit fuel to all to six valves.

Regulator of pressure of fuel

It settles down behind on the right on a distributive tube of fuel and should keep constant pressure of fuel in a distributive tube. It provides it by increase or reduction of quantity of the fuel flowing on рециркуляционной to a tube. If comes back more fuel, pressure goes down; at small return of fuel it rises.

At the expense of connection of a vacuum hose the pressure regulator simultaneously receives the information on a loading condition on the engine. At full loading it lifts pressure a little more. As a result of it it is injected more fuel which the engine requires for total power achievement.

The fuel pump and the relay

In more details you learn about the fuel pump with the electric drive, the relay of the fuel pump and other relays MPI/MPFI in the head the Fuel tank and the fuel pump.

Measuring instrument of pressure of fresh air

Only MPI

In a stream of soaked up air the wire which heats up an electric way is placed. Depending on weight of soaked up air the stream of air which cools a wire more strongly or more poorly changes. Temperature change causes change of resistance of a wire, and it is measured by the management block.

The gauge of pressure of air in an inlet collector

Only MPFI

The gauge of pressure of air in an inlet collector is in the block of management MPFI. The inlet collector and the gauge incorporate among themselves a thin hose. For the block of management pressure of air in an inlet collector is the major information for loading calculation on the engine. It influences duration of injection and at the moment of ignition.

The gauge of temperature of a stream of fresh air

Only MPFI

The gauge of temperature of soaked up air is screwed in in the channel всасывания the third cylinder (behind on the right). In addition to the gauge of pressure of air it serves the block of management for loading calculation on the engine. At a heat of soaked up air (it is equivalent low density of air) injection time, for example, should be reduced and the ignition moment hardly is more shifted in a direction "later".

Branch pipe throttle заслонки

There, where the stream of fresh air enters into an inlet collector of the engine, in the union there are two throttle заслонки. Smaller from them it is connected by a cable throttle заслонки to a pedal in salon. It doses out a stream of soaked up air in the engine before semigas position.

In process of increase in pressing at a pedal of gas the system of draughts opens the second, big заслонку until at full gas both completely will not be opened throttle заслонки.

Potentiometer throttle заслонки

The potentiometer throttle заслонки is put in action by its shaft. The potentiometer defines position throttle заслонки at present and in the form of electric pressure sends a signal to the management block. This information on loading, besides other signals, is used by the block of management for adjustment of idling, a choice of the characteristic of ignition and calculation of duration of injection.

The valve of stabilisation of idling

As it is clear under the name, this valve provides constant number of turns of idling – not important, the engine is heated-up or not, capacity consumers (climatic installation) are connected or not.

The valve thus is only an executive element. An adjustment brain is the block of management MPI or MPFI. It compares number of turns at present with nominal and provides the adjusted opening and the closing of the adjusting valve adjusting number of turns is thin. The cross-section section of the auxiliary air channel which bypasses throttle заслонку thus changes. If the auxiliary channel is opened, is soaked up more air and consequently the measuring instrument of a stream of fresh air "considers" that is opened throttle заслонка. It, in turn induces injection system to direct the necessary quantity of fuel that leads to increase of number of turns of the engine.

It is necessary to notice still that various valves of stabilisation of idling are applied: бесступенчатый regulating valve MPI; the valve with a drive from the so-called step-by-step electric motor at MPFI. Last changes an aperture байпаса the small, precisely adjusted steps.