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Audi A4, S4since 2000 releaseRepair and operation of the car |
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Audi A4, S4 + Introduction + Governing bodies and methods of safe operation + Current leaving and service + Engine + Cooling systems, heating and air conditioner + Power supply systems, release and decrease in toxicity of the fulfilled gases - Systems of electric equipment of the engine + System of ignition and engine management + System of preheat of the diesel engine - Diagnostics of systems of electronic control and diagnostic equipment General information Diagnostics of electronic control systems of the engine, injection, ignition and auxiliary brake systems The controler of interface of the personal computer to onboard system of self-diagnostics of OBD II under protocols of the SAE standards (PWM and VPW) and ISO 9141-2 Application of an oscillograph for supervision of signals in chains of control systems + Systems of charging and start + Manual box of gear shifting + 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 are suitable for check of the electric chains which are in a static state, and also for fixing of slow changes of the traced parameters. When carrying out the dynamic checks which are carried out on the working engine and also at identification of the reasons sporadic failures the oscillograph becomes absolutely irreplaceable tool. Some oscillographs allow to keep oscillograms in the built-in module of memory with the subsequent conclusion of results to the press or their transfer to the carrier of the personal computer already in stationary conditions. The oscillograph allows to observe periodic signals and to measure tension, frequency, width (duration) of rectangular impulses, and also levels of slowly changing tension. The oscillograph can be used for:
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 brought below typical for various sensors and actuation mechanisms of automobile control systems of temporary dependences. Parameters of periodic signals
Usually characteristics of the faulty device strongly differ from reference that allows the operator easily and quickly visually to reveal the refused component. Signals of a direct current - only signal tension is analyzed. Signals of this sort are developed by the devices given on illustrations below. Signals of alternating current - are analyzed amplitude, frequency and a form of a signal.
Frequency-modulated signals - are analyzed amplitude, frequency, a form of a signal and width of periodic impulses. Sources of similar signals are the devices given on illustrations below. The signals modulated on width of an impulse (ShIM) - are analyzed amplitude, frequency, a form of a signal and porosity of periodic impulses. Sources of similar signals are the devices given on illustrations below. The form of the signal which is given out by an oscillograph depends on a set of various factors and can change considerably. In a look told before starting replacement of the suspected component in case of discrepancy of a form of the removed diagnostic signal with the reference oscillogram, it is necessary to analyse carefully received result. Tension
In chains of a direct current amplitude of a signal is limited to supply voltage. It is possible to give a chain of system of stabilization of turns of idling (IAC) which alarm tension does not change with change of turns of the engine in any way as an example. In chains of alternating current signal amplitude already unambiguously depends on the frequency of work of a source of a signal, so, amplitude of the signal which is given out by the sensor of provision of a cranked shaft (CKP) will increase with increase of turns of the engine. In a look told if amplitude of the signal removed by means of an oscillograph is excessively low or high (up to trimming of top levels), it is only enough to switch the working range of the device, having passed to the corresponding scale of measurement. Frequency Frequency of repetition of alarm impulses depends on the working frequency of a source of signals. The form of the removed signal can be edited and brought to a look, convenient for the analysis, by switching on an oscillograph of scale of temporary development of the image.
As it was already told above, for reduction of a signal to a legible look it is enough to switch the scale of temporary development of an oscillograph. In certain cases characteristic changes of a signal are developed specularly rather reference dependences that is explained by reversibility of polarity of connection of the corresponding element and, in the absence of a ban on change of polarity of connection, can be ignored in the analysis. Typical signals of components of control systems of the engine Modern oscillographs are usually equipped with only two alarm wires in a compartment with a set of the various probes allowing to carry out connection of the device practically to any device. The red wire is connected to a positive pole of an oscillograph and is usually connected to the plug of the electronic control unit (ECM). The black wire should be connected to reliably grounded point (weight). Injectors Control of composition of air and fuel mix in modern automobile electronic systems of injection of fuel is exercised by timely adjustment of duration of opening of electromagnetic valves of injectors. Duration of stay of injectors abroach is defined by duration of the electric impulses developed by the control unit given on an entrance of electromagnetic valves. Duration of impulses is measured in milliseconds and usually does not exceed the limit of the range of 1 - 14 ms.
The typical oscillogram of the managing director of operation of an injector of an impulse is given on an illustration above. Often on the oscillogram it is possible to observe also a series of the short pulsations following directly the initiating negative rectangular impulse and supporting the electromagnetic valve of an injector abroach, and also the sharp positive throw of tension accompanying the moment of closing of the valve. Serviceability of functioning of ECM can be easily checked by means of an oscillograph by visual supervision of changes of a form of the operating signal at a variation of working parameters of the engine. So, duration of impulses at an engine provorachivaniye on single turns has to be slightly higher, than during the operation of the unit on low turns. Increase of turns of the engine has to be followed by corresponding increase in time of stay of injectors abroach. This dependence is especially well shown when opening a butterfly valve by short pressing a gas pedal. By means of the thin probe from the set attached to an oscillograph connect a red wire of the device to the injector ECM plug of a control system of the engine. Reliably ground the probe of the second alarm wire (black) oscillograph. Analyse a form of the signal engine which is read out during a provorachivaniya. Having started the engine, check a form of the operating signal on single turns. Having sharply pressed a gas pedal, lift the frequency of rotation of the engine to 3000 rpm, - duration of the operating impulses at the time of acceleration has to increase considerably, with the subsequent stabilization at the level equal, or slightly smaller peculiar to idling turns. Fast closing of a butterfly valve has to lead to the oscillogram flattening confirming the fact of an overshoot of injectors (for systems with fuel supply trim). At cold start the engine needs some enrichment of air and fuel mix that is provided with automatic increase in duration of opening of injectors. In process of warming up duration of the operating impulses on the oscillogram has to be reduced continuously, gradually coming nearer to value, typical for single turns. In systems of injection in which the injector of cold start is not applied, at cold start of the engine the additional operating impulses which are shown on the oscillogram in the form of pulsations of variable length are used. Typical dependence of duration of the operating impulses of opening of injectors on a working condition of the engine is presented in the table provided below. Inductive sensors
The increase in turns of the engine has to be followed by increase in amplitude of the pulse signal developed by the sensor. Electromagnetic valve of stabilization of turns of idling (IAC) In automotive industry electromagnetic IAC valves of a set of various types which are giving out signals of also various form are used. The common distinctive feature of all valves is that fact that porosity of a signal has to decrease with increase of the load of the engine connected with inclusion of the additional consumers of power causing decrease of turns of idling. If porosity of the oscillogram changes with increase in loading, however at inclusion of consumers violation of stability of turns of idling takes place, check a condition of a chain of the electromagnetic valve, and also correctness of the given-out ECM of a command signal. Usually in chains of stabilization of turns of idling the 4-polar step electric motor which description is given below is used. Check of 2-contact and 3-contact IAC valves is made in a similar manner, however oscillograms of the alarm tension which is given out by them are absolutely unlike. Step electric motor, reacting to the given-out ECM the pulsing operating signal, makes step correction of turns of idling of the engine according to the working temperature of cooling liquid and the current load of the engine. Levels of the operating signals can be checked by means of an oscillograph which measuring probe is connected serially to each of four plugs of the step motor. Warm up the engine up to the normal working temperature and leave it working at single turns. For increase in load of the engine include headlights, the air conditioner, or, - on models with the power steering, - turn a steering wheel. Turns of idling have to fall for a short time, however right there again be stabilized due to operation of the IAC valve.
Lambda probe (oxygen sensor)
Connect an oscillograph between the plug a lambda probe on ECM and weight. Make sure that the engine is heated-up up to the normal working temperature.
If the removed signal is not wavy, and represents linear dependence, that, depending on tension level, it testifies to excessive reimpoverishment (0 - 0.15 In), or reenrichment (0.6 - 1 In) air and fuel mix. If on single turns of the engine the normal wavy signal takes place, try to squeeze out several times sharply gas loops, - fluctuations of a signal should not exceed the limit of the range of 0 - 1 Century. The increase in turns of the engine has to be followed by increase of amplitude of a signal, reduction - decrease. Sensor of a detonation (KS) Connect an oscillograph between the plug of the sensor of a detonation of ECM and weight. Make sure that the engine is heated-up up to the normal working temperature.
At insufficient image sharpness slightly knock on the block of cylinders around placement of the sensor of a detonation. If it is not possible to achieve unambiguity of a form of a signal, replace the sensor, or check a condition of an electrical wiring of its chain. Ignition signal at the exit of the amplifier Connect an oscillograph between the plug of the amplifier of ignition of ECM and weight. Warm up the engine up to the normal working temperature and leave it working at single turns. At increase in turns of the engine the frequency of a signal has to increase in direct ratio. Primary winding of the coil of ignition Connect an oscillograph between the plug of the coil of ignition of ECM and weight. Warm up the engine up to the normal working temperature and ostavtey working at single turns.
Unevenness of throws can be caused by the excessive resistance of a secondary winding, and also malfunction of a condition of VV of a wire of the coil or a candle wire. |
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