Audi 80/Avant (B4)

since 1991-1995 of release

Repair and car operation

Cхема in detail shows ignition and injection system on a MPFI system example with the pressure sensor in an inlet collector. On the left side sensors and the sensors influencing behavior of the control unit are located. On the right components of systems of ignition and injection to which the control unit sends the teams are presented.

Cистема of injection of MPI/MPFI with т.з. supply of fuel

Electronics helps to constrain a few "appetites" of the engine even the most powerful Audi 80 version. However, at more than probable fuel consumption 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 engine capacity justifies this extra charge for high high-speed qualities of the car.

Multipoint injection

The 2,8-liter engine is supplied with injection system with MPI designation. Behind this reduction the English words Multi Point Injection – in Russian «multipoint injection» disappear. (The distinctive sign of system of injection of 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-liter engine is called MPFI actually only for their distinction. This reduction is in turn deciphered as Multi Point Fuel Injection – that is in Russian «multipoint injection of fuel». (A distinctive sign of system – absence an airmeasure).

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

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

Additional functions

• MPI/MPFI is very difficult system of the injection which control unit in addition includes also electronic system of ignition.
• The control unit of system of injection of MPI/MPFI is completely suitable for diagnostics. It means that malfunctions arising during operation register in memory of the store of malfunctions which is erased only after shutdown of the storage battery.
• Feature – storing even short-term malfunctions. From practice it is known that it is those defects which are extremely difficult for finding.
• 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.

Control unit

Between arriving (from various sensors) the control unit is information and vpryskny nozzles. He allows the engine, depending on operating conditions of loading and temperature, to receive precisely certain amount of fuel. For achievement of it the control unit varies duration of opening of nozzles with an electromagnetic drive. As pressure in system of supply of fuel constantly remains almost invariable, the amount of injected fuel can be regulated only by means of change of duration of injection. From where the control unit receives information according to which he establishes this duration of injection? For it various sensors answer:

• Only the 2,8-liter engine with system of injection of MPI: air flowmeter; it issues information on amount of the arrived air.
• Only the 2,6-liter engine with system of injection of MPFI: the temperature sensor in a final collector; he reports in a combination to the pressure sensor in an inlet collector (in the control unit) size of amount/weight of the arrived air.
• The sensor of temperature of cooling liquid; he reports size of temperature of the engine.
• Butterfly valve potentiometer; it gives information on load of the engine.
• Sensor of frequency of turns; it transmits a signal about frequency of rotation for system of ignition/injection of MPI/MPFI.
• Sensor of the moment of ignition; he reports about the provision of a cranked shaft. So the control unit learns, what cylinder on turn for ignition or injection.
• The signal of start-up arrives from the plug 50 (the ignition and starter lock switch).
• Lambda probes report, whether the mix structure is correct.
• Other indicators arrive from sensors of detonation combustion, from transmission, from a tachometer, even from the conditioner.

Vprysknye of a nozzle

In an inlet collector of each cylinder of the engine is on one vpryskny nozzle. They deliver to the corresponding cylinder amount of fuel necessary at present and at the same time provide thin dispersion of gasoline.

Nozzles are actuated by an electromagnet. Thus the needle of a spray rises from the saddle approximately on 0,1 mm – fuel can arrive. That circumstance is interesting that management of each separate vpryskny nozzle occurs precisely in an injection step. That means that injected fuel even has no time to be condensed on walls of an inlet collector (there are no fuel losses).

Fuel distributor

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

Regulator of pressure of supply 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 the drain highway. If on the drain highway more fuel leaves, pressure decreases; if it is less – pressure raises.

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

Fuel pump and relay

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

Air flowmeter

Only MPI

On a way of a stream of soaked-up air there is a wire which is warmed up electricly. Depending on the let-in quantity the air stream changes that leads to more or less strong cooling of the mentioned wire. Change of temperature leads to change of electric resistance of a wire which is measured by the control unit.

The pressure sensor in an inlet collector

Only MPFI

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

Sensor of temperature of inlet air

Only MPFI

The sensor 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 sensor in an inlet collector it is for the control unit an inofrmatsiya source for calculation of load of the engine. At high temperature 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.

Case of throttle knot

Where the stream of soaked-up air gets to an inlet collector of the engine, in one case there are two butterfly valves. Smaller from a zaslonok it is connected by means of a hummock drive to an accelerator pedal. It doses out a stream of inlet air in the engine before situation by a loading half. By further pressing an accelerator pedal the lever of draft opens the second, big zaslonka until in the provision of full loading there are no completely open both zaslonka.

Butterfly valve potentiometer

The potentiometer of a butterfly valve is put in action by the butterfly valve roller. The potentiometer defines the provision of a butterfly valve at present time and hands over to the control unit this information in the form of electric resistance. The control unit needs 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.

Valve of stabilization of frequency of idling

As it is already clear according to 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 such as the conditioner.

Thus the valve – executing body. The center of regulation is the control unit of systems of injection of MPI or MPFI. It compares frequency of rotation at present with standard and thus provides the coordinated 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 butterfly valves thus varies. When the channel is open, the bigger amount of air, thereby a flowmeter of air is let in or the pressure sensor in a final collector because of increase in amount of air "thinks" that the butterfly valve is open. That in turn gives the grounds to system of injection to increase amount of arriving fuel to the necessary.

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