Audi 80/Avant (B4)
since 1991-1995 release
Repair and operation of the car
+ Technical specification
+ 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 Mono-Motronic
+ System of injection Digifant
+ System of injection KE-III-Jetronic
- Systems of injection of MPI and MPFI
Malfunctions and independent diagnostics
Check of separate elements
Removal of elements
Hummock drive of "gas"
Check of the mode of idling and analysis of exhaust gases
List of malfunctions
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Anti-blocking system of brakes
+ Wheels and tires
+ Body electrical system
+ System of ignition
+ Signaling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ Body elements
+ Search of malfunctions
Interaction of components
The pistons rising and falling at the working engine involve air. If you completely squeeze out an accelerator pedal, then the engine soaks up the greatest possible number of air because in this case both butterfly valves are completely open. Respectively at the closed or partially open provision of butterfly valves the amount/weight of air is less. For neat job of the engine inlet air has to be mixed to fuel in precisely certain proportion. For definition of a proportion of fuel/air the system of injection of MPI uses the mass of inlet air. The air flowmeter at the same time is the MPI control unit a source of information of inlet mass of air. The comparable size of system of injection of MPFI – information on pressure in a final collector and about temperature.
For start of the cold engine it is necessary enriched – that is with the increased content of fuel – mix because fuels, many of droplets, are condensed on internal walls of system of injection already on the way to combustion chambers, that is do not participate in combustion process. Therefore, it is necessary to enrich mix.
Phase of warming up of the engine
After start the enriched mix as a fuel quantity still continues to be condensed in system of an admission is also necessary for the engine during some time. For this purpose there is "a poststarting enrichment". During certain time depending on temperature the bigger amount of fuel arrives. The control unit obtains necessary information on engine temperature from the sensor of temperature of cooling liquid.
At the closed butterfly valve (the released accelerator pedal) a small amount of air passes through the channel by a butterfly valve. The amount of this air is defined by a flowmeter of air or the sensor of pressure and is supplemented with necessary amount of fuel for receiving mix for the idling mode. By the way, mix for the mode of idling is richer in comparison with usual mix that becomes in order that the engine worked exactly, without differences of ignition. At what moment it is necessary to make enrichment for idling mix, the control unit learns from a potentiometer of a butterfly valve. How many air will pass through байпас (and, thereby, and rotation frequency range in the idling mode), defines the valve of stabilization of frequency of rotation of a shaft of the engine in the idling mode.
In the mode of partial loading the engine receives normal portions of fuel. At the same time the maximum attention is paid to perhaps more economic fuel consumption.
If the pedal of an accelerator is suddenly squeezed out, then it causes enrichment of mix for acceleration in case increase of the amount/weight of inlet air in a second exceeds a certain size. Also the signal of dispersal arrives from a potentiometer of a butterfly valve. If the engine still cold, then dispersal requires a bigger amount of fuel. The control unit therefore distinguishes the corresponding impulse of a flowmeter of air or the sensor of pressure and a potentiometer of a butterfly valve as a signal of dispersal and increases fuel supply.
The potentiometer of a butterfly valve signals the control unit that the driver completely squeezed out an accelerator pedal. For achievement of the maximum load the engine receives the enriched mix (enrichment for the mode of full loading).
Interruption in supply of fuel in the mode of compulsory idling (the movement by a setup)
If the car goes downhill and at the same time the accelerator pedal is not squeezed out, then the engine does not need fuel supply. The car moves itself under the weight or by inertia. On the high frequency of rotation and the provision of the closed butterfly valve (by means of a potentiometer of a butterfly valve) the control unit distinguishes the mode of compulsory idling (the movement by a setup) and can switch in the provision of "fuel economy".
Restriction of frequency of rotation
The system of injection compares the operating rotation frequency with maximum, making 6500 rpm, and at excess it just stops fuel supply (see also head Dvigateli).