Mercedes S-Class W-140

In 1991-1999 editions

Repair and enterprise of the car

Mercedes S-Class
+ Mercedes Benz cars of the class S (W-140)
+ operation manual
+ Routine maintenance
+ motor
+ cooling systems, heating
+ Systems of power supply and edition
- Electric equipment of the motor
   - Systems of ignition and management of the motor - the general information
      Checks of tax system ignition and injections
      Search of defects - the general information and preliminary checks
      Check and regulation of a corner of Zuvorkommens of ignition
      Spark plugs
      Self-diagnostics of control systems of the pipe OBD
      Diagnostics of electronic system of the automatic conditioner of air (kilowatt)
      Application of an oscillograph for observation of signals of tax system
      Ignition coils - a device detail
      Removal, device and regulation of a sensor of provision of a wave of curve (CMP)
      The distributor of ignition (M119.97 motors) - a device detail
   + systems of freight and start
+ gear shifting boxes
+ Awtomatitscheckaja transmission
+ connection
+ brake system
+ Aufhängung and management
+ body
+ electric onboard equipment

Application of an oscillograph for observation of signals of tax system

General information

Digital multimeters come nearer for check of electric chains which are in a static state, and also for fixing of slow changes of the checked characteristics perfectly. When conducting dynamic checks which are filled on the working motor and also when tracing the reasons of single violations very irreplaceable tool will be an oscillograph.

Several oscillographs allow to preserve Oszillogramme in the installed memory module with the following conclusion of results on the press or its Swap-In on the carrier of the personal computer already in stationary conditions.

The oscillograph allows to observe periodic signals and, effort, to measure the frequency, width (term) of rectangular impulses, and also levels of gradually changing efforts. The oscillograph can be used at execution of the following procedures:

   a) tracing of violations of unstable character;
   b) check of results of the made corrections;
   c) monitoring of activity of the probe ljambda of tax system of the motor equipped with the catalytic reformer;
   d) the analysis of the signals made by the probe ljambda which deviation of characteristics of norm is by all means the evidence of violation of serviceability of functioning of tax system in general. On the other hand, correctness of a form of the impulses exposed by a sensor can serve for a sure guarantee of lack of violations in tax system.

Reliability and simplicity of the enterprise of modern oscillographs do not demand from the operator of special special knowledge and experience is not present. Interpretation of the obtained information can be easily made by means of elementary visualen of comparison of Oszillogramme accepted during check with following temporary dependences which are typical for various sensors and actuation mechanisms of automobile tax systems.

Characteristics of periodic signals

General instructions

Characteristics of any periodic signal

Each signal accepted by means of an oscillograph, can be described by means of the following key parameters:

   Amplitude: the maximum and minimum efforts () a signal within the period;
   b) period: term of a cycle of a signal (Ms.);
   c) frequency: quantity of cycles for a second (Gz);
   d) width: term of a rectangular impulse (Ms., mks);
   e) porosity: the repetition period relation to width (In foreign terminology is called porosity the characteristic a running cycle down, expressed in % it is used);
   f) signal form: sequence of rectangular impulses, separate marriage, Sinusoide, sägezahnförmigen impulses, etc.

Usually characteristics of wrong establishment from strongly differ reference that easily allows the skilled operator and it quickly to give the refusing component by means of the analysis of the relevant Oszillogramms in day.

Signals of a direct current

The only performance data of such signals is an effort.

Signals of a direct current are made by the following devices:

Sensor of temperature of the cooled liquid of the motor (ECT)

Sensor of temperature of the absorbed air (IAT)

Sensor of situation drosselnoj saslonki (TPS)

The warmed-up probe ljambda

Measuring device of spatial costs of current of air (VAF)

Measuring device of mass of air (MAF)

Signals of alternating current

The main characteristics of these signals are the amplitude, frequency and a form of a signal.

Sensor of explosion (KS)

Inductive sensor of changes of the motor

The signals (TSCHM) modulated by tschastotno

Performance data of the modulated tschastotno of signals are the amplitude, frequency, a form of a signal and width of periodic impulses.

Sources of TSCHM of signals are the following devices:

Inductive sensor of provision of a bent shaft (CKP)

Inductive sensor of provision of a wave of curve (CMP)

Inductive sensor of speed of the movement of the car (VSS)

Workers on effect of the hall sensors of changes and the provision of waves

Optical sensors of changes and provision of waves

Digital sensors of thermo-metric measurement of mass of air (MAF) and absolute pressure in the pipeline of access (MAP)

Signals, modulates on width of an impulse (SCHIM)

Performance data of signals of modulation of width of an impulse (SCHIM) are the amplitude, frequency, a form of a signal and porosity of periodic impulses.

Sources of signals of SCHIM are the devices presented on the following illustrations:

Inschektory of fuel

Devices of stabilization of changes of idling (IAC)

Initial parcels of the coil of ignition

Electromagnetic Durchblasens gate of a coal adsorber (EVAP)

Gates of the rezirkuljazii system of the working gases (EGR)

The coded sequence of rectangular impulses

Performance data are the amplitude, frequency and a form of the sequence of the separated impulses.

Similar floor signals the module of memory of self-diagnostics makes ECM of tax system the motor.

Signal of Kodes of defect of the module of self-diagnostics of tax system the motor (to a code in 1223)

By means of the analysis of width and a form of impulses, and also calculation of its quantity in each of groups Kodes of defects kept in memory can be schitana.

Amplitude and form of a signal constantly remain, the written-down value will be issued until memory of the module is not cleared.

Oszillogramme interpretation

The form of the signal exposed by oscillographs depends on the mass of various factors and considerably can change. It is said by a look it is necessary before beginning compensation of the suspected component in case of discrepancy of a form of the accepted diagnostic signal with reference Oszillogramm, to analyze carefully received result.

Digital signal

Similar signal

Effort

Cannot zero level of a reference signal as absolute basic value, - consider "zero" real signal, depending on concrete characteristics of the tested chain, it can be moved concerning reference [1] within a certain admissible volume.

The tested contour removes the full amplitude of a signal from working tension, and also can exchange in certain borders concerning reference value [3 and [2].

In chains of a direct current amplitude of a signal is limited in working tension. As it is possible to give an example a chain of system of stabilization of changes of idling (IAC) which alarm effort does not change at change of changes of the motor in the way.

In chains of alternating current signal amplitude unambiguously depends already on the frequency of wear of a source of a signal, amplitude of a signal which is exposed by a sensor of provision of a bent shaft (CKP) at increase in changes of the motor will increase.

To switch by a look it is said if amplitude of the signal accepted by means of an oscillograph is excessively low or it is high, (up to trimming of top levels), it is enough only the working volume of the device, passed to the corresponding scale of measurement.

When checking the equipment of chains with electromagnetic management (for example, the IAC system) at power off throws of effort [4] which in the analysis of results of measurement can quietly be ignored can be observed.

It is necessary for itself also at emergence of such deformations of Oszillogramms not to disturb as skaschiwanije of the lower part of a facade of rectangular impulses [5] if, naturally, the fact wypolaschiwanija of the front is not a sign of violation of serviceability of functioning of the tested component.

Frequency

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

The form of the accepted signal can be edited to a look, convenient for the analysis, by means of switching on an oscillograph of scale of temporary palpation of the image and to be brought.

At observation of signals in chains of alternating current temporary palpation of an oscillograph depends on the frequency of a source of a signal [3], defines with changes of the motor.

As it is even higher, to switch the scale of temporary palpation of an oscillograph for the management of a signal to look udobotschitajemomu enough.

In several cases there is Oszillogramm of a signal develops like a mirror concerning reference dependence that rewersiwnostju of polarity of accession of the corresponding element clears up and, in the absence of the ban of change of polarity of accession, can be ignored in the analysis.

Typical signals of components of tax systems motor

Modern oscillographs need to be carried out only 2 alarm lines together with the offer variously of schtschupow, allowing usually equipped, connection of the device is valid to any establishment.

The red line joins in a positive pole of an oscillograph and usually joins to a clip of the electronic module of management (ECM). The black line is necessary to include it, too of course, sasemlennoj to point (weight).

Inschektory of an injection

Control of composition of mix of combustible air in modern electronic autosystems of an injection of fuel is exercised by means of timely correction of term Aufmachens of electromagnetic inschektorow gates.

The term of stay of inschektorow abroach clears up from term is made from the module of management of electric impulses which are served on an entrance of electromagnetic gates. The term of impulses becomes measured in milliseconds and usually it does not appear from a frame of volume of 1 ÷ 14 Ms.

Typical Oszillogramm of the operating wear of inschektora of an impulse — an impulse of management of Aufmachens inschektora of an injection of fuel

Often on Oszillogramm it is possible to observe also a series of short pulsing which support following directly introductory negative rectangular impulse and the electromagnetic inschektora gate abroach, and also a strong positive throw of effort, the moment of closing of the gate it is accompanied.

Serviceability of functioning of ECM can be easily checked by means of an oscillograph by means of visualen of observation of changes of a form of the operating signal at a variation of performance data of the motor. Thus the term of impulses at motor proworatschiwanii on not aggravated changes owes be slightly higher, than in operating time of the device on low changes. Increase in changes of the motor has to be followed by the corresponding increase in time of stay of inschektorow abroach. This dependence is shown when opening drosselnoj saslonki the short seals on the accelerator pedal especially well.

By means of thin schtschupa from the offer enclosed to an oscillograph you include the red line of the device to inschektornoj of a clip of ECM of tax system the motor. Schtschup of the second alarm line (in black color) an oscillograph, of course, sasemlite.

Analyze a form it is selected during signal motor proworatschiwanija.

The motor started you check a form of the operating signal on not aggravated changes.

Pressed strongly the accelerator pedal, you lift the frequency of Drehens of the motor to 3000 rpm, - the term of the operating impulses has to increase during acceleration considerably, with the following stabilization at the level is identical, or hardly small typically idling changes.

Bystry closing of drosselnoj saslonki has to go to sprjamleniju Oszillogramme, confirming the fact perekrywanija inschektorow (for which give systems with fuel transfer otsekanijem).

At cold start the motor needs some enrichment of mix of combustible air that is guaranteed at automatic increase in term of Aufmachens inschektorow. Depending on warming up the term of the operating impulses has to be reduced by Oszillogramm continuously, to value, typical for not aggravated changes, gradually bringing closer.

In systems of an injection in which inschektor of cold start is not used at cold start of the motor the additional operating impulses which are shown on Oszillogramm in the form of pulsing of variabelen of length are used.

Typical dependence of term of the operating impulses of Aufmachens inschektorow is presented in the following table by working position of the motor.

Condition of the motor	The term of the operating impulse, Ms.
Not aggravated changes	1.5 ÷ 5
In 2000 + 3000 rpm.	1.1 ÷ 3.5
Full gas	8.2 ÷ 3.5

Inductive sensors

Start the motor and compare Oszillogramm which is accepted by an exit of an inductive sensor with given on an illustration reference.

Increase in changes of the motor has to be followed by increase in amplitude of the impulse signal made by a sensor.

Electromagnetic gate of stabilization of changes of idling (IAC)

In automotive industry there will be electromagnetic IAC gates of mass of various types, various signals also a form give out is used.

The general sign of all gates is the fact that themselves porosity of a signal with increase of load of the motor connected with the appendix of additional consumers of the power, immersion of changes of idling called has to reduce.

If porosity of Oszillogramms at increase in loading changes, violation of stability of changes of idling is available, nevertheless, at the appendix of consumers, check a condition of a chain of the electromagnetic gate, and also correctness ECM of a signal of command is exposed.

It is usually used in chains of stabilization of changes of idling 4-poljusnyj the electric motor of a step which description nizheperechisleno. Check of 2 contact gates and contact gates 3 IAC is made in a similar manner, however, Oszillogramme of the alarm efforts exposed by them are very dissimilar.

The step electric motor, on ECM the pulsing operating signal is exposed reacting, makes the classified correction of changes of idling of the motor according to the worker of temperature of the cooled liquid and the current load of the motor.

Levels of the operating signals can be checked by means of an oscillograph, measuring schtschup joins alternately each 4 clips of the motor of a step.

Heat the motor up to normal working temperature and give from his worker on not aggravated changes.

For increase in load of the motor there will be header searchlights which accept the air conditioner, or, - on models with the steering drive with a servomechanism, - you turn a steering wheel. Idling changes for a short time have to fall to be stabilized, however, here again due to wear of the IAC gate.

Compare the accepted Oszillogramm with given on an illustration reference.

Probe ljambda (oxygen sensor)

Oszillogramme which are typical for used by cars in the frequent Estonian the probes ljambda zirkonijewogo type in which the basic effort 0.5B is not used are given in office. Lately sensors of the titan which working volume of a signal 0 ÷ 5 forms In gain the increasing popularity, and the high level of effort at combustion of abgereicherten of mix is issued, low, - enriches.

Include an oscillograph between a probe ljambda clip on ECM and weight.

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

Compare it is displayed the measuring Oszillogramm device with the reference dependence given on an illustration.

If the accepted signal not wavy, and linear dependence, it, depending on the level of effort represents, it testifies about pereobednenii (0 ÷ 0.15), or pereobogaschtschenii (0.6 ÷ 1) about mix of combustible air is raised.

If on not aggravated changes of the motor the normal wavy signal is available, пытаьтесь repeatedly strongly to express gas pedel, - fluctuations of a signal of volume of 0 ÷ 1 W. should not surpass borders

Increase in changes of the motor has to be followed by increase in amplitude of a signal, reduction - immersion.

Sensor of explosion (KS)

Include an oscillograph between a clip of a sensor of explosion of ECM and weight.

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

Strongly you express the accelerator pedal and you compare a form of the accepted signal of alternating current with reference brought on the illustration Oszillogramm.

At insufficient sharpness of the image legonko you tap the block of cylinders in placement of a sensor of explosion.

If it is not possible to strive for unambiguity of a form of a signal, replace KS sensor, or check a condition of the electric leading device of its chain.

Ignition signal at the exit of the amplifier of ignition

Include an oscillograph between a clip of the amplifier of ignition of ECM and weight.

Heat the motor up to normal working temperature and give from his worker on not aggravated changes.

Oscillograph the sequence of rectangular impulses of a direct current has to be released. Compare a form of the received signal with reference brought on the illustration Oszillogramm, motionless attention to an obrushivaniye of such characteristics as amplitude, the frequency and a form of impulses devoting.

At increase in changes of the motor the frequency of a signal has to increase absolutely in proportion.

Initial parcels of the coil of ignition

Include an oscillograph between a clip of the coil of ignition of ECM and weight.

Heat the motor up to normal working temperature and give from his worker on not aggravated changes.

Compare a form of the received signal with reference brought on the illustration Oszillogramm, - positive throws of effort have to have constant amplitude.

Unevenness of throws can be caused by the increased resistance of repeated Wickelns, and also to defect of a condition of the WW line of a roll of a film or the line of candles.