Audi A4

since 1994 of release

Repair and car operation



A4 Audi
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ exhaust System
+ cooling System
+ Fuel tank and fuel pump
+ Air filter and absorption channels
- Injection system
   + System of injection of Motronic
   - System of injection of MPI and MPFI
      Additional functions
      Knots of system of injection
      Functioning
      Adjustment with the help a lambda probe
      Violations in work and self-diagnostics
      Self-help
      Visual control
      Check of knots
      Dismantle of separate details
      Butterfly valve cable
      Inlet collector
      Idling adjustment
      Check of exhaust gases
      The help at malfunctions
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
+ Electrotechnical equipment
+ ignition System
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ body Details
+ Salon
Search of malfunctions
Technical characteristics





Knots of system of injection

In order 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 Sensor of number of turns of the engine
2 — the Sensor of the moment of ignition
3 — the Hall Sensor
4 — the Sensor of temperature of cooling liquid
5 — the Sensor of temperature of soaked-up air
6 — the Potentiometer of a butterfly valve and the switch of a mode of idling
7 — the Sensor of a detonation of I
8 — the Sensor of a detonation of II
9 — the Lambda probe of I
10 — the Lambda probe of II
11 — injection Valves
12 — the Target cascade of capacity
13 — Coils of double ignition
14 — the Valve of stabilization of idling
15 — the Electromagnetic valve of system of the coal filter
16 — the Control unit heating a lambda probes
17 — the Relay of the fuel pump

This scheme illustrates the electric party of system of ignition/injection, in this case on MPFI example with the sensor of pressure of air in an inlet collector. On the left side sensors and sensors which influence behavior of the control unit take place. On the right those knots of ignition and injection to which the control unit sends the signals are represented.

Fuel party of system of ignition/injection of MPI/MPFI

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

3–injection valve.


The control unit (2) system of ignition/injection of MPI/MPFI is in an electronic box at the left behind in an impellent compartment (in the so-called moistening tank). In an arm near the control unit here in the engine with working volume of 2,6 l the relay (1) heating a lambda probes takes place.

At the left: injection valves (1, 2 and 3) in the six-cylinder engine are located 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 of 2,8 l priflantsovanny to the case of the air filter. Figure «2» designated the connection socket.

Control unit

Between entering information (from various sensors) and valves of injection there is an electronic control unit. Depending on existing conditions of loading and temperature it sends absolutely certain amount of fuel to the engine. For this purpose the control unit varies duration of opening of valves of injection operated by an electromagnetic way. The amount of injected fuel can change only at the expense of duration of injection. Information for determination of duration of injection arrives in the control unit from various knots, it:

  • Only in the engine of 2,8 l with MPI: measuring instrument of a stream of fresh air; from it information on amount of soaked-up air arrives.
  • Only in the engine 2,6 with MPFI: the sensor of temperature of soaked-up air; in a combination to the sensor of pressure of air in an inlet collector (in the control unit) it gives comparative size soaked up / oh amounts/masses of air.
  • The sensor of temperature of cooling liquid; it delivers comparative size of temperature of the engine.
  • Butterfly valve potentiometer; from it information on load of the engine arrives.
  • Sensor of number of turns; it transmits a signal about number of turns of the crankshaft.
  • The signal about start of the engine arrives from the plug 50 of the lock of ignition (starter).
  • Lambda probes send a signal about correctness of structure of a fuel and air mix.
  • Other sizes influencing, arrive from: sensors of a detonation, a transmission, a speedometer and if is, from climatic installation.

Injection valves

In the channel of absorption of each cylinder of the engine takes place on one valve of injection. It submits amount of fuel necessary at present to each cylinder and at the same time 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 supply of fuel to all valves of injection. Besides, the distributive tube functions as a collector and thanks to it does not allow pressure fluctuations. The ring-shaped form of the tube, allowing to submit fuel to all six valves is interesting.

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 amount of the fuel flowing on a retsirkulyatsionny tube. If more fuel comes back, pressure goes down; at small return of fuel it rises.

At the expense of connection of a vacuum hose the pressure regulator at the same time receives information on a condition of load of the engine. At full loading it lifts pressure a little more. As a result of it more fuel which the engine needs for achievement of full capacity is injected.

Fuel pump and relay

In more detail you learn about the fuel pump with the electric drive, the relay of the fuel pump and other MPI/MPFI relays in 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 more strongly or more poorly cools a wire changes. Change of temperature causes change of resistance of a wire, and it is measured by the control unit.

The sensor of pressure of air in an inlet collector

Only MPFI

The sensor of pressure of air in an inlet collector is in the MPFI control unit. The inlet collector and the sensor incorporate among themselves a thin hose. For the control unit pressure of air in an inlet collector is the major information for calculation of load of the engine. It influences duration of injection and at the moment of ignition.

Sensor of temperature of a stream of fresh air

Only MPFI

The sensor of temperature of soaked-up air is screwed in to the canal of absorption of the third cylinder (behind on the right). In addition to the sensor of pressure of air it serves the control unit for calculation of load of the engine. At high temperature of soaked-up air (it is equivalent low density of air) injection time, for example, should be reduced and the moment of ignition is slightly more shifted in the direction "later".

Butterfly valve branch pipe

Where the stream of fresh air enters into an inlet collector of the engine, in the union there are two butterfly valves. Smaller from them it is connected by a butterfly valve cable to a pedal in salon. It doses out a stream of soaked-up air in the engine to the provision of semi-gas.

In process of increase in pressing at a gas pedal the system of drafts opens the second, big zaslonka until at full gas both butterfly valves completely will not be open.

Butterfly valve potentiometer

The potentiometer of a butterfly valve is put in action by its shaft. The potentiometer defines the provision of a butterfly valve at present and in the form of electric tension sends a signal to the control unit. This information on loading, besides other signals, is used by the control unit for adjustment of idling, a choice of the characteristic of ignition and calculation of duration of injection.

Valve of stabilization of idling

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

The valve thus is only an executive element. A brain of adjustment is the MPI or MPFI control unit. 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 a butterfly valve thus changes. If the auxiliary channel is open, more air and consequently the measuring instrument of a stream of fresh air "considers" that the butterfly valve is open is soaked up. It, in turn induces system of injection to direct the necessary amount of fuel that leads to increase of number of turns of the engine.

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