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

Spark plugs

General description

The spark plug consists of the central electrode, the insulator with the case and a weight electrode(s). Between the central electrode and an electrode of weight the spark igniting fuel-air mix slips. It is not necessary to apply the spark plugs other than recommended. The recommended type of candles is defined among other things by kalilny number.

The Kalilny number characterizes degree of thermal loading of a candle. The kalilny number of a candle is lower, the degree of its thermal loading is higher. At the same time the candle takes away heat better thanks to what the possibility of kalilny ignition of fuel mix is excluded. The candle with the high thermal characteristic has that shortcoming that its temperature of self-cleaning lies above. It is more inclined to formation of a deposit, in particular when the engine in operating time often does not reach the working temperature, for example the movement in the city, short movements by winter.
The correct kalilny number of a candle is defined by the manufacturer of the car. There are candles with one or several electrodes of weight, with various length of a carving and its diameter. When replacing a candle it is necessary to establish only the candles corresponding to instructions of the manufacturer of the car.

Middle service life of a candle is various. At the same time a serious role is played also by material of electrodes. Chrome-nickel alloy is characterized by very high heat conductivity and high corrosion resistance. Silver possesses the best heat sink, and platinum electrodes have high corrosion resistance and firmness against an obgoraniye. Service life of candles lies between 20 000 and 100 000 km of a run, depending on material of electrodes and their number.

Depending on a design of engines distinguish two types of consolidation between spark plugs and a head of cylinders.

Flat consolidation has an external sealing ring which is not lost and is fixed on the candle case. At conical consolidation additional sealing elements are not required. At limited space for installation, candles with a flat landing surface and the turnkey small size are in most cases applied. Candles with a conic landing surface thanks to a compact design have the smaller sizes.
Spark plugs it is necessary to change each 60 000 km of a run (see the Head Routine maintenance).

On appearance of a candle it is possible to draw a conclusion on work of candles, quality management of mix and a condition of the engine (pistons, piston rings, etc.)

Coal deposits

Symptoms: Availability of soot indicates reenrichment of fuel-air mix or weak intensity of a spark. Causes admissions of ignition, complicates start and results in instability of operation of the engine.
Recommendations: Whether check the air cleaner is hammered whether fuel level in the float-operated camera is not too high, whether the air gate is jammed and whether contacts are not too worn-out. Try to use candles with longer insulator that increases the resilience to pollution.


Symptoms: Oiling of a candle is caused by wear of maslootrazhatelny caps. Oil gets to the combustion chamber through worn-out guides of valves or piston rings. Causes admissions of ignition, complicates start and results in instability of operation of the engine.
Recommendations: Perform mechanical recovery work and replace candles.

Normal state of a candle

Symptoms: Gray-brown color and easy wear of electrodes. The Kalilny number of candles corresponds to type of the engine and its general state.
Recommendations: When replacing candles establish candles of the same type.


Symptoms: Soft deposits of brownish color on one or both electrodes of a candle. A source of their education are the applied additives to oil and/or fuel. Excessive accumulation can lead to isolation of electrodes and cause admissions of ignition and unstable operation of the engine at acceleration.
Recommendations: At bystry accumulation of deposits change maslootrazhatelny caps that will prevent hit of oil in combustion chambers. Try to replace fuel brand.


Symptoms: Porous, white insulator, erosion of electrodes and lack of any deposits. Leads to reduction of service life of a candle.
Recommendations: Check whether the kalilny number of the established candles conforms to requirements of Specifications, whether the ignition advancing corner is correctly exposed, whether too poor fuel-air mix moves, whether there is no leak of vacuum of the inlet pipeline and whether valves are jammed. Check also the level of a cooler and whether the radiator is corked.


Symptoms: A rounding off of electrodes with a small congestion of deposits on the working end. Color is normal. Leads to difficulty of start of the engine in cold damp weather and to increase in fuel consumption.
Recommendations: Change candles on new, the same type.

Too early ignition

Symptoms: are melted off. The insulator has white color, but maybe is polluted owing to admissions of ignition or hit in combustion chambers of foreign particles. Can lead to an engine exit out of operation.
Recommendations: Check kalilny number of the established candles, an ignition advancing corner, quality of mix (whether it is not too grown poor) whether the cooling system is corked and whether the lubrication system normally functions.


Symptoms: Insulators can be chopped off or burst. Also inaccurate technology of adjustment of a candle gap can lead to damage of the insulator. Can lead to damage of pistons.


Symptoms: After admissions of ignition during a long period of adjournment can be loosened at preservation of working temperature in the combustion chamber. At high speeds of adjournment in flakes come off the piston and stick to the hot isolation center, causing admissions of ignition.
Recommendations: Replace candles or smooth out and establish into place old.

Electroconductive luster

Symptoms: The insulator has yellowish color and the polished appearance. Speaks about sudden temperature increase in combustion chambers at sharp acceleration. Usual deposits at the same time are melted off, taking a form of a varnish covering. Leads to admissions of ignition at high speeds of the movement.
Recommendations: Replace candles (colder, at preservation of a manner of driving).

Mechanical damages

Symptoms: Can be caused by hit of foreign materials in the combustion chamber or arise at blow of the piston about too long candle. Lead to refusal of functioning of the cylinder and to damage of the piston.
Recommendations: Remove foreign particles from the engine and/or replace

Short circuit of electrodes

Symptoms: Waste of products of combustion gets to interelectrode space. Firm deposits accumulate, forming a crossing point between electrodes. Leads to refusal of ignition in the cylinder.
Recommendations: Remove deposits from interelectrode space.

At a vvinchivaniye of candles you watch that they were not drawn as the sealing washer can be damaged. Do not exceed the inhaling moment specified in Specifications.