Mercedes of the S-class W202

1993-2000 of release

Repair and operation of the car

Mercedes W202
+ 1.2. General information
+ 2. Maintenance
+ 3. Engines
+ 4. Lubrication system
+ 5. Cooling system
+ 6. Heating, ventilation
+ 7. System of ignition
- 8. Fuel system
   + 8.1.1. Introduction
   + 8.2. System of injection of petrol engines
   + 8.3. System of injection and power supply of diesel engines
   - 8.4. System of production of exhaust gases
      8.4.2. Main and average mufflers
      8.4.3. Cars with the catalyst
      8.4.4. Device of neutralization of exhaust gases of the diesel car
      8.4.5. Rub in one – or how to save the catalyst
+ 9. Transmission
+ 10. Running gear
+ 11. Steering
+ 12. Brake system
+ 13. Body
+ 14. Electric equipment
+ 14.2. Electrical circuitries

8.4.5. Rub in one – or how to save the catalyst


Replacement of the failed catalyst will run into money therefore well to foreknow what problems with it happen as the situation with them in the market of spare parts is.

Until recently we knew about the catalyst only the following: it is such piece which it is unclear why it is necessary, it is unclear as works that our gasoline "kills" it, generally – one troubles. To cut out – and any problems! But gradually we began to get used that the catalyst – a thing after all reasonably useful, at least thoughts of "surgical intervention" in the exhaust system visit more and more seldom and the lesser number of the heads.

In the spring when the staff of GAI begins "fight for purity of air", one more problem falls down us – it is necessary to adjust WITH. Owners of the cars equipped with catalysts do not even think of it, and check posts WITH pass without shiver in knees and fear for the purse. However, the same purse can decently "lose weight" for other reason. Penalties for excess of the SO level will seem cheap in comparison with expenses on purchase and replacement of the catalyst if it fails. Therefore absolutely not harmfully to the nobility as to treat it, and for this purpose it is necessary to understand at first as it устрон and as works.

How they work?

At combustion of working mix a number of unhealthy products of the person of combustion, in particular, carbon monoxide (SO), various hydrocarbons (SN) and oxides of nitrogen (NO) is formed. Though these substances also make only 1% of the general exhaust (the rest is a nitrogen, carbon dioxide and water vapor), they are very harmful and demand neutralization. There are several ways of fight against harmful exhausts – for example, impoverishment of mix which the engine or recirculation of an exhaust uses – but any of them will not be compared by efficiency to catalytic converter.

As experts speak, catalytic converter is a simple device in which there is a difficult chemical process. "In the case from stainless steel there is ceramic or metal "brick" having cellular structure. At this monolith huge surface area, and all it is covered with the thinnest layer of special alloy – actually the catalyst containing platinum, rhodium and palladium. These precious metals are responsible for wonderful properties of the catalyst, they determine its high cost".

Exhaust gases "wash" a monolith surface, and when temperature reaches "critical" value of 270 °C, catalytic reaction begins. Carbon monoxide turns into dioxide (carbon dioxide), hydrocarbons turn into water and besides carbon dioxide, and oxides of nitrogen turn into water and nitrogen. All this is less harmful to the environment.

Catalytic converters are capable to reduce quite effectively toxicity of an exhaust, at the same time they do not influence consumption of fuel and engine capacity. In the presence of the catalyst the return pressure of an exhaust slightly increases from what the engine loses 2–3 h.p., but it is, practically, all "payment" for cleaning of an exhaust. However, installation of catalytic converter – not the ideal decision. Theoretically, it has to serve infinitely as above-mentioned precious metals serve only as the catalyst which at chemical reaction, as we know, is not spent. In practice life of the catalyst has the limit...

What ruins them?

The refusal of catalytic converter can happen for several reasons though, usually, it is process gradual which cannot be caught without the special equipment.

"Core" of the majority of catalysts is made of ceramics - the material known for the fragility. The car can get at a speed to a hollow, hit against something or it is even simple "to strike" the catalyst case on a stone, and from it catalytic "brick" can burst. After that loss by "core" of the working qualities – a matter of time.

The converters of new generation containing a metal monolith are not so vulnerable in this respect. It is possible to break them, of course, but, in any case, it is not so simple.

Enemies of the catalyst

Except physical destruction there is one more frequent reason of failure of the catalyst. Fuel. It is extremely sensitive to composition of fuel. If gasoline ethylated, then the lead tetraethyl which is contained in it is laid on an active surface of catalytic "brick" and quickly "salts" it from what any reactions stop. Apparently, at gas stations and tips of hoses began to put the different size, and paint distributing columns in different colors, and write about it at every turn, and all the same consumers sometimes confuse and fill not in that gasoline. And it is enough "to burn" a half-tank of such gasoline, and the catalyst will die irrevocably.

But not only ethylated gasoline – the enemy of the catalyst. The catalyst can be ruined and unleaded if the control system of the engine is faulty, incompleteness mix burns down or the engine is strongly worn-out.

Threefold catalytic converters ("threefold" because as the catalyst serves set of three precious metals) install only on those cars which engines are equipped with the closed exhaust control system. In front of the catalyst the oxygen sensor which traces structure of an exhaust and transfers these data to the central processing unit is installed. Depending on the content of oxygen in an exhaust, BEU regulates composition of gas mixture and ignition so that their optimum values were maintained. It serves as the main protection for the catalyst, and also provides economy of fuel and overall performance of the engine. The catalyst does not transfer big deviations as a part of working mix. Badly adjusted engine with the increased content of hydrocarbons in an exhaust just ruin the catalyst. If mix too poor, it can cause a sharp overheat of the catalyst what the monolith, only already "physically" again will suffer from. Thus, "life" of the catalyst depends on serviceability of a control system of the engine.

A lot of things depend also on serviceability of the most oxygen sensor. With "age" it becomes "lazy" or absolutely fails that affects composition of mix and, respectively, serviceability of the catalyst.

Can damage the catalyst also an exhaust of strongly worn-out engine burning oil. It, getting together with an exhaust to the catalyst, "is baked" on a monolith surface, like a varnish, and does not allow the catalyst to work.

There are also other harmful factors. For example – candles. Improper candles will not give full combustion that can cause pernicious reaction of fusion in the catalyst".

Be very careful in use of gasoline additives or to oil. The majority does not think of it, and additives can harmfully influence the catalyst too. If on a product it is not written: "it is compatible to the catalyst", do not risk better.

One more dangerous case – start of the engine towage. At the same time there can be a hit in the catalyst of just pure gasoline. It, first, poisons the catalyst, but also can cause instant reaction and even explosion. You look also where you go – try not to get to deep pools. Working temperature of the catalyst makes about 900 °C. Its sudden hit in water can be fatal.

In general, it is noticed that service life of the catalyst is influenced by service conditions. More catalysts by the cars operated in city conditions when the engine is often started suffer. On the other hand, at long high-speed driving on highways the catalyst also spoils from what overheats.

At last, you arrive reasonably if you begin to examine all system of an exhaust regularly. If arms are broken or rubber suspension brackets fell off, the exhaust pipe will vibrate, transferring unnecessary loads to the catalyst.