Audi 80/Avant (B4)

Since 1991-1995 of release

Repair and car operation

Audi 80/Avant
+ The description
+ Engines
+ System of release of the fulfilled gases
+ Cooling system
+ Fuel tank and the fuel pump
+ The air filter and воздухозаборные channels
- Injection system
   + System of injection Mono-Motronic
   + System of injection Digifant
   + System of injection KE-III-Jetronic
   - Systems of injection MPI and MPFI
      Operating procedure
      Malfunctions and independent diagnostics
      Independent repair
      Visual check
      Check of separate elements
      Removal of elements
      Trosovyj drive of "gas"
      Check of a mode of idling and the analysis of exhaust gases
      The list of malfunctions
+ Coupling
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
+ Antiblocking system of brakes
+ Wheels and tyres
+ Kuzovnaja electrosystem
+ Ignition system
+ Illumination
+ Signalling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ Body elements
+ Search of malfunctions
+ Specifications


Systems of injection MPI and MPFI

Cхема in detail shows ignition and injection system on an example of system MPFI with the pressure gauge in an inlet collector. On a left-hand side gauges and the sensor controls influencing behaviour of the block of management are located. On the right components of systems of ignition and injection to which the management block sends the commands are presented.

Cистема injection MPI/MPFI with т.з. Fuel givings

1 – a regulator of pressure of giving of fuel;
2 – the fuel distributor;

3 – впрыскная an atomizer.

Electronics helps to constrain a few "appetites" of the engine even the most powerful version Audi 80. However, at more than probable expense of fuel over 12 l on 100 km not always it is possible to be quite convinced that this good intention is carried out. But nevertheless follows that high capacity of the engine justifies this extra charge for high high-speed qualities of the car.

Multidot injection

The 2,8-litre engine is supplied by system of injection with designation MPI. Behind this reduction English words Multi Point Injection – in Russian multidot injection disappear. (The Distinctive sign of system of injection MPI is a flowmeter of air in an air inlet sleeve behind on the right in a motor compartment).

Almost identical system of injection of the 2,6-litre engine is named MPFI actually only for their distinction. This reduction is in turn deciphered as Multi Point Fuel Injection – that is in Russian multidot injection of fuel. (The Distinctive sign of system – absence воздухомера).

The technical distinctive sign of these both systems is a way of measurement of quantity (or weights) arriving air:

    MPI applies for this purpose термоанемометрический воздухомер with a heated up thread. MPFI applies for this purpose the pressure gauge in a final collector (it is built in a monitor and is connected with a final collector a connecting hose), and also the gauge of temperature of arriving air (in a final collector).

Additional functions

    MPI/MPFI Is very difficult system of the injection which block of management in addition includes also electronic system of ignition. The block of management of system of injection MPI/MPFI is completely suitable to diagnostics. It means that malfunctions arising during operation register in memory of the store of malfunctions which is erased only after switching-off of the storage battery. Feature – storing even short-term malfunctions. From practice it is known that it those defects which are extremely difficult for finding out. After 50 starts of the engine the malfunction which has arisen only once, is erased from memory of the store of malfunctions.

Basic elements

For the best understanding of the general functioning of this system of injection it is necessary to get acquainted with separate problems of components at first.

The management block

Between arriving (from various gauges) the management block is the information and впрыскными atomizers. He allows the engine, depending on operating conditions of loading and temperature, to receive precisely certain quantity of fuel. For achievement of it the management block varies duration of opening of atomizers with an electromagnetic drive. As pressure in system of giving of fuel constantly remains almost invariable, the quantity of injected fuel can be regulated only by means of change of duration of injection. Whence the management block receives the information according to which he establishes this duration of injection? For it various gauges answer:

    Only the 2,8-litre engine with system of injection MPI: air flowmeter; it gives out the information on quantity of arrived air. Only the 2,6-litre engine with system of injection MPFI: the temperature gauge in a final collector; he informs in a combination to the pressure gauge in an inlet collector (in the management block) size of quantity/weight of arrived air. The gauge of temperature of a cooling liquid; he informs size of temperature of the engine. Potentiometer throttle заслонки; it gives the information on loading on the engine. The gauge of frequency of turns; it transmits a signal about frequency of rotation for system of ignition/injection MPI/МPFI. The gauge of the moment of ignition; he informs on position of a cranked shaft. So the management block learns, what cylinder on turn for ignition or injection. The start-up signal arrives from the plug 50 (the ignition and starter lock-switch). Ljambda-probes inform, whether the mix structure is correct. Other indicators arrive from gauges of detonation combustion, from transmission, from a tachometre, even from the conditioner.

Vprysknye atomizers

In an inlet collector of each cylinder of the engine is on one впрыскной to an atomizer. They deliver to corresponding cylinder quantity of fuel necessary at present and simultaneously provide thin dispersion of gasoline.

Atomizers are set in motion by an electromagnet. Thus the spray needle rises from the saddle approximately on 0,1 mm – fuel can arrive. That circumstance is interesting that management of everyone separate впрыскной atomizers occurs precisely in an injection step. That means that injected fuel even does not have time to be condensed on walls of an inlet collector (there are no fuel losses).

The fuel distributor

It is intended for uniform supply by fuel of all впрыскных atomizers. Besides, the fuel distributor operates and as the fuel store, thereby preventing pressure differences. The U-shaped form of the pipe, allowing a fuel supply to all is very interesting to six atomizers.

Regulator of pressure of giving of fuel

It is located behind on the right on the distributor of fuel and should – according to the name – to support constant level of pressure in the fuel distributor. It is carried out by means of more or less strong outflow of fuel back in a fuel tank on a drain highway. If on a drain highway leaves more fuel pressure decreases; if it is less – pressure raises.

Through connection of the vacuum pipeline to a pressure regulator the information on loading on the engine besides arrives. At full loading the regulator increases pressure even more. Thanks to it it is injected more fuel necessary for the engine for achievement of the maximum capacity.

The fuel pump and the relay

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

Air flowmeter

Only MPI

On a way of a stream of soaked up air there is a wire which is warmed up электрически. Depending on the let in quantity the air stream changes that leads more or to less strong cooling of the mentioned wire. Temperature change leads to change of electric resistance of a wire which is measured by the management block.

The pressure gauge in an inlet collector


The pressure gauge in an inlet collector is in the block of management MPFI. Connection between an inlet collector and the gauge represents a thin hose. Pressure in an inlet collector is for the block of management a front view of the information for calculation of loading of the engine. It influences duration of injection and the ignition moment.

The gauge of temperature of inlet air


The gauge of temperature of inlet air is screwed in in the inlet channel of the third cylinder (behind on the right). In addition to the pressure gauge in an inlet collector it is for the block of management of a source инофрмации for loading calculation on the engine. At a heat of inlet air (that is equivalent low density of air) it is necessary to reduce, for example, duration of injection and to shift the ignition moment aside "later" a little.

The case of throttle knot

There, where the stream of soaked up air gets to an inlet collector of the engine, in one case there are two throttle заслонки. Smaller from заслонок it is connected by means of тросового a drive to an accelerator pedal. It doses out a stream of inlet air in the engine before position половинной loadings. By the further pressing a pedal of an accelerator the draught lever opens the second, big заслонку until in position of full loading there are no completely opened both заслонки.

Potentiometer throttle заслонки

The potentiometer throttle заслонки is put in action by the platen throttle заслонки. The potentiometer defines position throttle заслонки at present time and hands over to the management block this information in the form of electric resistance. The management block requires this information on loading, for example, for regulation of frequency of rotation in a mode of idling, a choice of the characteristic of ignition and calculation of duration of injection.

The valve of stabilisation of frequency of idling

As it is already clear under the name, this valve constantly provides constant frequency of rotation of a shaft of the engine in an idling mode – all the same, whether the engine is cold or heated-up, are included or not powerful consumers of the electric power of type of the conditioner.

Thus the valve – executing body. The regulation centre is the block of management of systems of injection MPI or MPFI. It compares frequency of rotation at present with standard and thus provides the co-ordinated opening and closing of the regulating valve for an equilibration of frequency of rotation is thin. The cross-section section of the additional air channel laid bypassing throttle заслонок thus varies. When the channel is opened, let in большее quantity of air, thereby a flowmeter of air or the pressure gauge in a final collector because of increase in quantity of air "thinks" that is opened throttle заслонка. That in turn gives the grounds to injection system to increase quantity of arriving fuel to the necessary.

It is necessary to notice still that in different systems of injection different valves for stabilisation of frequency of rotation operate: in system of injection MPI – smoothly regulating; in system of injection MPFI – put in action the so-called step-by-step engine. This last regulates opening of channels in small, is thin the adjusted steps.