Mercedes S-Class W-140

1991-1999 of release

Repair and operation of the car



Mercedes S-Class
+ Mercedes-Benz cars of the class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ Cooling systems, heating
+ Power supply system and release
- Engine electric equipment
   - Systems of ignition and engine management - the general information
      Checks of a control system of ignition and injection
      Search of malfunctions - the general information and preliminary checks
      Check and adjustment of a corner of an advancing of ignition
      Spark plugs
      Self-diagnostics of systems of electronic control of OBD
      Diagnostics of electronic system of the automatic air conditioner (AC)
      Application of an oscillograph for observation of signals of a control system
      Ignition coils - installation details
      Removal, installation and adjustment of the sensor of position of the camshaft (CMP)
      The distributor of ignition (M119.97 engines) - installation details
   + Systems of a charge and start
+ Gear shifting box
+ Automatic transmission
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment






Checks of a control system of ignition and injection

General information

Components of system of ignition are very reliable. Malfunctions are, as a rule, connected with unreliability or pollution of contacts. Breakdowns of high-voltage wires most often arise because of pollution, humidity or damage of isolation, but not because of malfunction of components of system. Before drawing a conclusion on malfunction of any component, check its conducting.

To check operability of a high-voltage wire, having removed it from a candle and having brought closer to the surface of the engine (watching existence of a spark), it is impossible. You risk not only to receive blow by current, but also to damage the control unit or the coil of ignition. If the engine works unstably, never remove tips of wires from candles for definition of faulty.

The checks described below should be carried out if malfunction is obvious (refusal of a starter, admissions of ignition, etc.). Some malfunctions are less obvious and can not be shown because the control system of the engine switched in the mode of safe functioning. Malfunctions of this sort are shown in increase in fuel consumption, instability of turns of idling, loss of power, a detonation, etc. If you found similar symptoms, address on HUNDRED.

The engine is not started

Keep in mind that at failure of the anti-theft device you will not be able to start the engine. Switch-off the device (address the Head the Operation manual)


If the engine is not turned at inclusion of a starter or turned very slowly, check a starter and the rechargeable battery. Attach the voltmeter to plugs of the battery and measure tension at an engine crankshaft provorachivaniye by a starter. Do not include a starter more, than for 10 seconds. If the voltmeter shows 9.5 B and less, be convinced of serviceability of the rechargeable battery, a starter and system of charging.

If at inclusion of a starter the engine rotates with a usual speed, but is not started, check all high-voltage components of system of ignition.

Following instructions of the manufacturer, connect a stroboscope and turn the engine crankshaft a starter. If the lamp on a stroboscope lights up, tension arrives on spark plugs. Be convinced of serviceability of candles. If the lamp is not lit, check high-voltage wires (see the Head Routine maintenance). If candles or wires are serviceable (the spark is), follow the recommendations provided in the Section Search of Malfunctions - the general information and preliminary checks.

If there is no spark, be convinced of serviceability of the coil of ignition (or replace the coil with obviously serviceable or check resistance of windings). If malfunction is not found, look for it in other place. If after replacement of the coil the engine began to be started - malfunction is found. You do not hurry to throw out the coil and to buy new. Be convinced of reliability of accession of conducting to the coil (the engine could not be started because of the oxidized contact).

If the coil as it should be, it is faulty, possibly, the powerful buffer output cascade which is an engine control unit component, one of sensors of a control system of the engine or the accompanying knot. In this case in memory of the control unit the malfunction code which can be considered from memory has to be written down.

Codes of malfunctions can be considered by means of the special equipment.

Admissions of ignition

Most often the unreliable contact of conducting with plugs of the coil of ignition or any sensor is the reason of admissions of ignition.

Switch off ignition and be convinced of reliability of connection of all sockets of system of ignition.

Check high-voltage wires. Make sure that they are reliably fixed in points of intermediate fastenings and do not adjoin to metal parts of the engine. If the wire concerns metal and it damaged isolation, then during the operation of the engine the spark will be given not on a candle, and on weight. At detection even of insignificant damage of isolation at least of one wire replace all set.

It is possible to be convinced of full operability of wires, having temporarily replaced them with obviously serviceable.

When replacing wires change them on one. It you will avoid risk of the wrong connection. Do not damage a wire at installation.

If high-voltage wires are completely serviceable, most likely, the coil of ignition or any spark plug is the reason of emergence of admissions of ignition. Establish a new set of candles (see the Head Routine maintenance) or check the coil (see the Section Check and adjustment of a corner of an advancing of ignition). The faulty or dirty sensor of position of the crankshaft can be the cause of admissions of ignition (see the Section Power supply system and injection of fuel of the petrol engine - the general information of the Head of the Power supply system and release.

If check of above-mentioned knots did not lead to improvement of operation of the engine, consider codes of malfunctions from memory of the control unit.












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