Audi A4, S4

Since 2000 of release

Repair and car operation



Audi A4, S4
+ Introduction
+ Controls and receptions of safe operation
+ Current leaving and service
+ The engine
+ Systems of cooling, heating and the air conditioner
+ Power supply systems, release and decrease in toxicity of the fulfilled gases
- Systems of an electric equipment of the engine
   + Ignition and engine management system
   + System of preheat of the diesel engine
   - Diagnostics of systems of electronic control and the diagnostic equipment
      The general data
      Diagnostics of electronic control systems by the engine, injection, ignition and auxiliary brake systems
      The controller of interface of the personal computer with onboard system of self-diagnostics OBD II under reports of standards SAE (PWM and VPW) and ISO 9141-2
      Application of an oscillograph for supervision of signals in chains of control systems
   + Gymnastics and start systems
+ Manual box of a gear change
+ Automatic transmission
+ Coupling, power shafts and differential
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment



Application of an oscillograph for supervision of signals in chains of control systems

Digital multimeters perfectly approach for check of electric chains being in a static condition, and also for fixing of slow changes of traced parametres. At carrying out of the dynamic checks which are carried out on the working engine, and also at revealing of the reasons sporadic failures by absolutely irreplaceable tool there is an oscillograph.

Some oscillographs allow to keep oscillograms in the built in module of memory with the subsequent conclusion of results to the press or their swapping to the carrier of the personal computer already in stationary conditions.

The oscillograph allows to observe periodic signals and to measure pressure, frequency, width (duration) of rectangular impulses, and also levels of slowly varying pressure.

The oscillograph can be used for:

  • Revealings of failures of astable character.
  • Checks of results of the made corrections.
  • The control of activity of a ljambda-probe of a control system of the engine equipped catalytic with the converter.
  • The analysis of the signals developed by a ljambda-probe which deviation of parametres from norm is unconditional the certificate of infringement of serviceability of functioning of a control system as a whole, - on the other hand, correctness of the form of impulses given out by a ljambda-probe can serve as a reliable guarantee of absence of infringements in a control system.

Reliability and simplicity of operation of modern oscillographs do not demand any special special knowledge and experience from the operator. Interpretation of the received information can be easily made by elementary visual comparison of the oscillograms removed during check with resulted more low typical for various gauges and actuation mechanisms of automobile control systems of time dependences.

Parametres of periodic signals

Each signal removed by means of an oscillograph, can be described by means of the following key parametres:

  • Amplitude: the Difference of the maximum and minimum pressure () a signal within the period;
  • The period: Duration of a cycle of a signal (мсек)
  • Frequency: Quantity of cycles in a second (Hz);
  • Width: Duration of a rectangular impulse (мс, мкс);
  • Porosity: the Relation of the period of repetition to width (In foreign terminology return is applied porosity parametre named a running cycle, expressed in %);
  • The signal form: Sequence of rectangular impulses, individual emissions, a sinusoid, sawtooth impulses, etc.

Usually characteristics of the faulty device strongly differ from reference that allows the operator easily and quickly visually to reveal the refused component.

Direct current signals - pressure of a signal is analyzed only.

This sort of signals are developed by the devices presented on illustrations more low.

The gauge of temperature of a cooling liquid of the engine (ECT)

The gauge of temperature of soaked up air (IAT)

The gauge of position throttle заслонки (TPS)

Warmed up ljambda-probe

Measuring instrument of the volume expense of a stream of air (VAF)

Measuring instrument of weight of air (MAF)

Alternating current signals - are analyzed amplitude, frequency and the signal form.

The detonation gauge (KS)

The inductive gauge of turns of the engine

The frequency-modulated signals - are analyzed amplitude, frequency, the form of a signal and width of periodic impulses. Sources of similar signals are the devices presented on illustrations more low.

The inductive gauge of position of a cranked shaft (CKP)

The inductive gauge of position of a camshaft (CMP)

The inductive gauge of speed of movement of the car (VSS)

Working on effect of the Hall gauges of turns and position of shaft

Optical gauges of turns and position of shaft

Digital gauges of thermometric measurement of weight of air (MAF) and absolute pressure in the inlet pipeline (MAP)

The signals modulated on width of an impulse (ШИМ) - are analyzed amplitude, frequency, the form of a signal and porosity of periodic impulses. Sources of similar signals are the devices presented on illustrations more low.

Injectors

Devices of stabilisation of turns of idling (IAC)

Primary winding of the coil of ignition

The electromagnetic valve of a purge of a coal adsorber (EVAP)

System valves recycling the fulfilled gases (EGR)

The form of a signal given out by an oscillograph depends on set of various factors and can change appreciably. In a kind told before to start replacement of a suspected component in case of discrepancy of the form of the removed diagnostic signal with the reference oscillogram, it is necessary to analyse the received result carefully.

Pressure

Digital signal

Analogue signal

Zero level of a reference signal cannot be considered as absolute basic value, - "zero" of a real signal, depending on concrete parametres of a checked chain, it can appear shifted concerning reference (the Digital signal [1] see) within a certain admissible range (the Digital signal [2] and the Analog signal [1] see).

The full amplitude of a signal depends on pressure of a food of a checked contour and also can vary concerning reference value in certain limits (the Digital signal [3] and the Analog signal [2] see).

In chains of a direct current the amplitude of a signal is limited to pressure of a food. As an example it is possible to result a chain of system of stabilisation of turns of idling (IAC) which alarm pressure does not change in any way with change of turns of the engine.

In chains of an alternating current the amplitude of a signal already unequivocally depends on frequency of work of a source of a signal so, the amplitude of the signal which is given out by the gauge of position of a cranked shaft (CKP) will increase with increase of turns of the engine.

In a kind told if the amplitude of a signal removed by means of an oscillograph appears excessively low or high (up to trimming of top levels), it is enough to switch only a working range of the device, having passed to a corresponding scale of measurement.

At check of the equipment of chains with electromagnetic management (for example, system IAC) at food switching-off can be observed throws of pressure [4], которыеможно easy ignore at the analysis of results of measurement.

It is not necessary to worry also at occurrence of such deformations of the oscillogram, as скашивание the bottom part of forward front of rectangular impulses [5] if, of course, the fact выполаживания front is not a sign of infringement of serviceability of functioning of a checked component.

Frequency

Frequency of repetition of alarm impulses depends on working frequency of a source of signals.

The form of a removed signal can be edited and led to a kind convenient for the analysis by switching on an oscillograph of scale of time development of the image.

At supervision of signals in alternating current chains time development of an oscillograph depends on frequency of a source of the signal [3], defined by engine turns.

As already it was told above, for signal reduction to a legible kind it is enough to switch scale of time development of an oscillograph.

In certain cases characteristic changes of a signal appear developed mirror concerning reference dependences that speaks реверсивностью polarity of connection of a corresponding element and, in the absence of an interdiction for change of polarity of connection, can be ignored at the analysis.

Typical signals of components of control systems of the engine

Modern oscillographs are usually equipped only by two alarm wires in a compartment with a set various probeов, allowing to carry out device connection practically to any device.

The red wire is connected to a positive pole of an oscillograph and usually connected to the plug of the electronic block of management (ECM). The black wire should be connected to reliably earthed point (weight).

Injectors

Management of structure of an air-fuel mix in modern automobile electronic systems of injection of fuel is carried out by timely updating of duration of opening of electromagnetic valves of injectors.

Duration of stay of injectors abroach is defined by duration developed by the block of management of the electric impulses submitted on an input of electromagnetic valves. Duration of impulses is measured in milliseconds and usually does not fall outside the limits a range 1 - 14 мс.

Impulse of management of opening of an injector of fuel

The typical oscillogram of an injector of an impulse operating operation is presented on an illustration above. Often on the oscillogram it is possible to observe also a series of the short pulsations following directly behind the initiating negative rectangular impulse and supporting the electromagnetic valve of an injector abroach, and also the sharp positive throw of pressure accompanying the moment of closing of the valve.

Serviceability of functioning ECM can be checked easily up by means of an oscillograph by visual supervision of changes of the form of an operating signal at a variation of working parametres of the engine. So, duration of impulses at проворачивании the engine on single turns should be a little above, than at unit work on low turns. Increase of turns of the engine should be accompanied by respective increase in time of stay of injectors abroach. The given dependence is especially well shown at opening throttle заслонки by short pressing a gas pedal.

By means of thin probeа from a set applied on an oscillograph connect a red wire of the device to инжекторной to plug ECM of a control system of the engine. Щуп the second alarm wire (black) oscillograph reliably earth.

Analyse the form read out during time проворачивании the signal engine.

Having started the engine, check up the form of an operating signal on single turns.

Sharply having pressed a gas pedal, lift frequency of rotation of the engine to 3000 rpm, - duration of operating impulses at the moment of an acceleration should increase considerably, with the subsequent stabilisation at level equal, or hardly smaller peculiar to idling turns.

Fast closing throttle заслонки should lead to the flattening of the oscillogram confirming the fact перекрывания of injectors (for systems with отсеканием fuel givings).

At cold start the engine requires some enrichment of an air-fuel mix that is provided with automatic increase in duration of opening of injectors. In process of warming up duration of operating impulses on the oscillogram should be reduced continuously, gradually coming nearer to value typical for single turns.

In injection systems in which the injector of cold start is not applied, at cold start of the engine the additional operating impulses shown on the oscillogram in the form of pulsations of variable length are used.

In the table resulted more low typical dependence of duration of operating impulses of opening of injectors on a working condition of the engine is presented.

Inductive gauges

Engine condition

Duration of an operating impulse, мс

Single courses

1.5 5

2000 3000 rpm.

1.1 3.5

Full gas

8.2 3.5

Start the engine and compare the oscillogram removed from an exit of the inductive gauge from the resulted reference.

The increase in turns of the engine should be accompanied by increase in amplitude of a pulse signal developed by the gauge.

The electromagnetic valve of stabilisation of turns of idling (IAC)

In motor industry electromagnetic valves IAC of set of the various types which are giving out signals also of the various form are used.

The general distinctive feature of all valves is that fact that porosity of a signal should decrease with loading increase for the engine, connected with inclusion of additional consumers of the capacity causing fall of turns of idling.

If porosity of the oscillogram changes with loading increase, however at inclusion of consumers infringement of stability of turns of idling takes place, check up a condition of a chain of the electromagnetic valve, and also correctness given out ECM a command signal.

Usually in chains of stabilisation of turns of idling the 4-polar step-by-step electric motor which description is resulted more low is used. Check of 2-contact and 3-contact valves IAC is made in a similar manner, however oscillograms of alarm pressure given out by them are absolutely unlike.

The step-by-step electromotor, reacting on given out ECM a pulsing operating signal, makes step updating of turns of idling of the engine according to working temperature of a cooling liquid and current loading on the engine.

Levels of operating signals can be checked up by means of an oscillograph, measuring probe which is connected serially to each of four plugs of the step-by-step motor.

Warm up the engine to normal working temperature and leave its working on single turns.

For increase in loading at the engine include headlights, air conditioner, or, - on models with the wheel hydraulic booster, - turn a steering wheel. Idling turns should fall to short time, however there and then again to be stabilised for the account of operation of valve IAC.

Compare the removed oscillogram to the resulted reference.

Ljambda-probe (the oxygen gauge)

In Section the oscillograms typical for oxygen gauges most often used on cars циркониевого of type in which basic pressure 0.5В is not used are resulted. Recently the increasing popularity is got by titanic gauges, рабочийдиапазон which signal makes 0 - 5 In, and high level of pressure stands out at combustion of the impoverished mix, low, - enriched.

Connect an oscillograph between the ljambda-probe plug on ECM and weight.

Make sure that the engine is heated-up to normal working temperature.

Compare the oscillogram displayed a measuring instrument to the resulted reference dependence.

If the removed signal is not wavy, and represents linear dependence, that, depending on pressure level, it testifies to excessive repauperization (0 - 0.15), or reenrichment (0.6 - 1) an air-fuel mix.

If on single turns of the engine the normal wavy signal takes place, try to squeeze out sharply some times педель gas, - signal fluctuations should not fall outside the limits a range 0 - 1 Century

The increase in turns of the engine should be accompanied by increase of amplitude of a signal, reduction - decrease.

The detonation gauge (KS)

Connect an oscillograph between the plug of the gauge of detonation ECM and weight.

Make sure that the engine is heated-up to normal working temperature.

Sharply squeeze out a pedal of gas and compare the form of a removed signal of an alternating current to the resulted reference oscillogram.

At insufficient image sharpness slightly knock on the block of cylinders around placing of the gauge of a detonation.

If to achieve unambiguity of the form of a signal it is not possible, replace the gauge, or check up a condition of electroconducting of its chain.

Ignition signal on an amplifier exit

Connect an oscillograph between the plug of the amplifier of ignition ECM and weight.

Warm up the engine to normal working temperature and leave its working on single turns.

On the oscillograph screen the sequence of rectangular impulses of a direct current should stand out. Compare the form of an accepted signal to the resulted reference oscillogram, paying steadfast attention to coincidence of such parametres, as amplitude, frequency and the form of impulses.

At increase in turns of the engine frequency of a signal should increase in direct ratio.

Primary winding of the coil of ignition

Connect an oscillograph between the plug of the coil of ignition ECM and weight.

Warm up the engine to normal working temperature and оставьтеего working on single turns.

Compare the form of an accepted signal to the resulted reference oscillogram, - positive throws of pressure should have constant amplitude.

Non-uniformity of throws can be caused excessive resistance of a secondary winding, and also malfunction of condition ВВ of a wire of the coil or a candle wire.