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
   - System of injection of MPI and MPFI
      Additional functions
      Knots of system of injection
      Adjustment with the help a lambda probe
      Violations in work and self-diagnostics
      Visual control
      Check of knots
      Dismantle of separate details
      Cable of a butterfly valve
      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
+ System of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ body Details
+ Salon
Search of malfunctions
Technical characteristics


The coordinated work of separate details

When the engine works, the pistons rising and falling in cylinders soak up air. If you completely wring out a gas pedal, the engine soaks up the maximum quantity of air as in this case both butterfly valves are completely open. It is necessary for a neat job of the engine that with the soaked-up air fuel in an exact proportion mixed up. For definition of a proportion of air and gasoline in working mix in MPI the mass of the soaked-up air is used. In MPFI as comparative size information on pressure serves in an inlet collector and temperature.

Now the control unit can give the correct signals for opening and closing of valves of injection. Long opening is provided for big amount of fuel, short time — at need for a small amount of fuel.


For start of the cold engine more saturated is necessary, i.e. working mix rich with fuel as the set of droplets of fuel settles on walls in the field of absorption on their way to combustion chambers and does not participate in combustion process any more. Therefore the fuel share in fuel and air mix has to be raised.

During management of start of the cold engine injection duration valves increases. Such factors as temperature of cooling liquid and frequency of rotation of the engine, influence injection duration. After a certain number of turns of the engine the amount of fuel necessary for start of the cold engine, slowly decreases and starts corresponding to the standard.

Heated-up engine

After start the engine some time needs the enriched working mix as still certain amount of fuel is condensed in the field of absorption. For this purpose there is "a poststarting increase". Depending on temperature some time moves more fuel. The control unit receives the necessary information on engine temperature from the sensor of temperature of cooling liquid.

Engine oil, quite viscous at the cold engine, causes the increased internal friction in the car. The increased effort to hold engine turns is necessary. Already mentioned idling stabilization valve is intended for ensuring giving of this increased amount of working mix.


At the closed butterfly valve via the roundabout channel round a butterfly valve a small amount of air is carried out. This air is fixed by the air stream measuring instrument, or pressure sensor and therefore in working mix for idling it is supplemented with necessary amount of fuel. In general working mix idling contains more gasoline, than at usual operation in order that the engine worked exactly and trouble-free in ignition.

The amount of air passing the roundabout channel (and, therefore, number of turns of the engine idling), is defined by the idling stabilization valve.

Partial loading

At partial loading the engine receives standard amount of fuel. Thus significance is attached to fuel consumption minimization.


If the gas pedal is suddenly wrung out, the enrichment of fuel and air mix necessary for acceleration when the gain of the soaked up amount/weight of air in a second exceeds a certain size is caused. Also the potentiometer of a butterfly valve gives a signal of acceleration. At the cold engine accelerations require bigger amount of fuel. Therefore the control unit estimates each impulse of the measuring instrument of a stream of fresh air or a sensor of pressure and a potentiometer of a butterfly valve as a signal of acceleration and increases fuel supply.

Full loading

The potentiometer of a butterfly valve shows to the control unit that the driver completely wrung out a gas pedal. To develop the maximum power, the engine receives more enriched working mix now (enrichment of working mix at full loading).

Mode of compulsory idling

At the movement downhill with the released gas pedal it is not necessary to give fuel to the engine. The car itself slides at the expense of the weight or dispersal. On high turns of the engine and the provision of a butterfly valve (from its potentiometer) the control unit learns when there is a mode of compulsory idling, and can "save fuel".

Restriction of number of turns

The system of injection compares the frequency of rotation of the engine to the maximum number of turns in 6500 rpm at present and at their excess simply closes "the crane with fuel".