Mercedes S-Class W-140

1991-1999 of release

Repair and car operation

Mercedes S-Class
+ Mercedes-Benz Cars of a class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ Systems of cooling, heating
+ Power supply system and release
- Engine electric equipment
   - Ignition and engine management systems - the general information
      Checks of a control system by 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 conditioner of air (KV)
      Oscillograph application for supervision of signals of a control system
      Ignition coils - installation details
      Removal, installation and adjustment of the sensor of provision of a camshaft (CMP)
      The ignition distributor (M119.97 engines) - installation details
   + charge and start Systems
+ gear shifting Box
+ Avtomaticheckaya transmission
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment


Search of malfunctions - the general information and preliminary checks

Address also to Diagnostics of malfunctions Introductionsthe Section

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 carrying out diagnostics. At malfunction emergence the control unit writes down some sequence of signals (a malfunction code) which it is possible to consider subsequently as the special device (see in memory. 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 electroconducting).

It is not enough visual check of electroconducting and sockets - surely consider information which is storing 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. Probably, the reason is covered in carelessly established component or unreliably attached socket.

If you try to find the reason of a certain malfunction of the engine, for example capacity falling, in addition to the actions given below measure a compression in cylinders. Be convinced that the fuel filter and an air purifier changed according to the ordered intervals.

Keep in mind that after reading of codes of malfunctions it is necessary to remove them 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 absence 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 (interfaced surfaces should be absolutely pure and without corrosion traces) with a body or the engine.

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

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

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

After restoration of the damaged wire correctly arrange it in an impellent compartment, far from 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 should be established. If on an internal surface of the socket you cover up corrosion traces (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 is necessary to replace it. 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 preserving greasing then establish into place. You can learn greasing type on HUNDRED.

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

Attentively examine all vacuum hoses and the tubes located in an impellent 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 передавлены and are bent too strongly, i.e. do not pass air. Special attention give to the hoses located near keen edges, and also the ends of all hoses. It is necessary to replace all damaged hoses.

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 by 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 pairs of oil in combustion chambers. At pollution or blocking of these hoses the engine will unstably work (especially at single turns).

Following from a 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. Special attention give to junctions of tubes. On them there can be the cracks leading to leakages of fuel.

Uncover cases of an air purifier and examine an element. It should be rather pure and dry. Strongly polluted cleaner shows strong resistance to an air stream that leads to appreciable decrease in engine capacity. Replace an air purifier if necessary.

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

At performance of any works in an impellent compartment at the working engine be extremely careful.

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

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

Watch the hands, do not allow hit of long hair or clothes in an impellent compartment. Steer clear of system of release and other hot details.

Following from an air inlet to an air purifier and further to a throttle, be convinced of absence of leaks from hoses of supply of air (including nearby vacuum hoses). They can be found on characteristic whistle. If whistle is not distributed, put 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 start 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 absence of leakages of gases. For simplification of work you can lift the car on the lift, establish on a platform or over a hole. For carrying out the simplest check stop up a final opening of system of release and listen to system work. 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 moving of each socket on the corresponding plug at the working engine. 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, it is necessary what in certain cases 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 service station for carrying out more careful diagnostics with use of the special equipment.