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


Search of malfunctions - the general information and preliminary checks

Address also Diagnostics of malfunctionsthe Section Introductions

The system of ignition and fuel system are the interconnected components of a control system of the engine.

General information

The system of ignition and fuel system have the general diagnostic system intended for preservation of codes of malfunctions and performing diagnostics. At malfunction emergence the control unit writes down in memory some sequence of signals (a malfunction code) which can be considered the special device subsequently (see the Section Self-diagnostics of Systems of Electronic Control of OBD).

If failures in operation of the engine of the car are observed, the reason of it, most likely, can be found out, having investigated memory of the control unit. After reading of codes of malfunctions it is possible to find out what knot is faulty and to execute the corresponding checks (either the knot, or its electrical wiring).

Visual check of an electrical wiring and sockets is not enough - surely consider information which is stored in memory of the control unit.

Preliminary checks

If malfunction arose soon after service of any knot, first of all carefully check this knot and surrounding space. Perhaps, the reason is covered in carelessly installed component or unreliably attached socket.

If you try to find the reason of a certain malfunction of the engine, for example falling of power, in addition to the actions given below measure a compression in cylinders. Make sure that the fuel filter and the air cleaner changed according to the ordered intervals.

Keep in mind that after reading of codes of malfunctions they need to be removed from memory of the control unit by means of the same diagnostic scanner then to eliminate malfunction.

Open a cowl and be convinced of reliability of accession of tips of wires to plugs of the accumulator and lack of corrosion on them. At detection of traces of corrosion or damages replace or clear wires. Similarly check all tires of grounding, having convinced that they provide reliable contact (the interfaced surfaces have to be absolutely pure and without corrosion traces) with a body or the engine.

After that attentively examine all visible conducting laid in a motive compartment. Be convinced of reliability of all connections. At this stage you are interested in obviously damaged wires. They can be cut or ground about the sharp or moving engine knots, for example, of a detail of a suspension bracket or a driving belt. The break of a wire can result from negligent installation of any knot. The wire can melt at contact with system of release. The wrong laying of its plaits in a motive compartment after performance of repair or service of any knot is the most probable cause of damage of conducting.

Wires can be damaged or short-circuited without damage of their isolation. In this case survey will not lead to anything. Similar damages can arise after a pulling of wires or the wrong placement of conducting in a motive compartment. If you consider that similar damage is possible, check a wire, following the sequence stated below.

The damaged wire can be repaired, having sealed a piece of a new wire in a gap. The soldering is necessary for receiving reliable contact. Isolation can be restored enough an insulating tape or a thermoshrinkable tube. If damages are considerable and the damaged wire plays an essential role, the most right exit (though) replacement of the corresponding plait on new will be rather expensive.

After restoration of the damaged wire correctly arrange it in a motive compartment, far from the rotating and hot knots. Do not forget to fix a wire in intermediate clamps (if is).

Be convinced of reliability and purity of all available sockets. All clamps have to be established. If on the internal surface of the socket you cover up corrosion tracks (white or green deposits, and also rust traces) or excessive pollution, remove it from the corresponding plug and carefully clear. For this purpose you can use special spray. If the socket is seriously damaged, it should be replaced. Keep in mind that in certain cases you should replace a plait entirely.

If you could remove completely corrosion traces from the socket, fill it with the preserving lubricant then establish into place. You can learn lubricant type on HUNDRED.

On all models the inductive sensor of position of the crankshaft is installed (also VMT of the first cylinder decides on its help). On models of early release its working part can be polluted by oil or dust that can lead to failures in its work and, respectively, to admissions of ignition. The sequence of actions at removal and installation of the sensor is given in the Head of the Power supply system and release.

Attentively examine all vacuum hoses and tubes located in a motive compartment. Be convinced of reliability of an inhaling of collars and lack of cracks, stratifications and traces of damages on hoses. Be convinced also that no hoses not of a peredavlena and are bent too strongly, i.e. do not pass air. Pay special attention to the hoses located near keen edges and also the ends of all hoses. All damaged hoses need to be replaced.

Be convinced of lack of traces of damages and pollution on hoses of system of ventilation of a case. Be convinced also that they are not blocked from within. The quantity and installation sites of hoses of system depends on car model, but on all models the hose connecting the top part of the engine to a hose an air inlet or the inlet pipeline is established. Hoses of system connect also the block of cylinders (or a maslozalivny mouth) to the inlet pipeline. These hoses deliver oil vapors in combustion chambers. At pollution or blocking of these hoses the engine will unstably work (especially at single turns).

Following from the fuel tank via the fuel filter to the fuel distributive highway along fuel pipelines, attentively examine them. At detection of traces of damages or excesses replace the corresponding section. Pay special attention to junctions of tubes. On them there can be cracks leading to fuel leak.

Uncover the case of the air cleaner and examine an element. It has to be rather pure and dry. Strongly polluted cleaner shows strong resistance to an air stream that leads to noticeable deceleration of power of the engine. Replace the air cleaner if necessary.

Start the engine and leave it to work at single turns.

When performing any works in a motive compartment at the working engine be extremely careful.

Besides high probability of receiving burns from the heated details of the engine or system of release, you risk to suffer a serious injury from the rotating details (for example, the fan of a radiator or a driving belt).

Before work, first of all take measures and observe safety measures stated at the beginning of each Chapter.

You watch the hands, do not allow hit of long hair or clothes in a motive compartment. You steer clear of system of release and other hot details.

Following from an air inlet to the air cleaner and further to a throttle, be convinced of lack of leaks from air supply hoses (including nearby vacuum hoses). They can be found on characteristic whistle. If whistle does not sound, apply a small amount of soap water on suspicious section of a hose. If the hose is damaged, kind of work of the engine will change, and on the processed surface of a hose there will be bubbles (or, depending on pressure in a hose, water can begin to be soaked up inside). At leak detection reliably tighten a collar or replace the damaged hose.

Similarly check all system of release (from a collector to back section). Be convinced of lack of leak of gases. For work simplification you can lift the car on the elevator, establish on a platform or over a hole. For conducting the simplest check stop up the outlet of system of release and listen to work of system. If you heard characteristic whistle, leak takes place. At detection of leak tighten the corresponding collar, bolts or nuts, replace laying or the burned-through section.

Further check consists in serial movement of each socket on the corresponding plug at the working engine. The unreliable contact will be determined by change of kind of work of the engine. Restore reliability of contact, having replaced or having cleared the corresponding socket. Keep in mind that in certain cases it is necessary to change the whole plaits.

If as a result of preliminary checks you did not find the reason of unstable operation of the engine, the car should be driven away on the station of service for performing more careful diagnostics with use of the special equipment.