Catalytic converter: monster under the bottom

Car manufacturers began using catalytic converters in the last century to reduce the toxicity of exhaust gases of a car engines with spark ignition.

Inside the neutralizer there is a porous carrier material - a ceramic block with honeycomb structure. On the surface of this ceramic block there is an intermediate layer of activators and over it will be a catalytically active layer of precious metals (platinum, palladium and rhodium). It is the catalytic layer where chemical reactions occur - the toxic substances of exhaust gases (carbon monoxide and nitrogen oxides) are converted to carbon dioxide and elemental nitrogen, and hydrocarbons are converted to carbon dioxide and water vapor. The degree of exhaust gases purification in an efficient neutralizer reaches 98%.

Catalytic converter works without the active substance consumption. In most modern vehicles with Euro-4 and Euro-5 toxicity standards, catalytic converters are located as close as possible to the engine outlets and bolted through the gasket to the cylinder head.

Such close proximity of the massive and hot catalytic converter to the engine makes it difficult to assemble the engine compartment and leads to an increase in the temperature there. But on the other hand the catalytic converter core is warming up much faster after the engine is started. After all, only the properly heated catalytic converter can effectively purify the exhaust gases. Catalytic reactions are effective only at temperatures above 300 degrees Celsius.

For proper system operation in front of the catalytic unit and immediately behind it there will be installed oxygen sensors (lambda probes). Sensor standing before the neutralizer is called the controller, and the one behind it is called diagnostic.

There is also another catalytic converter arrangement used the world practice. Such a scheme with the keg of the catalytic converter located under the bottom of the car appeared at the dawn of this method of reducing the toxicity of exhaust gases and is still used, for example, in Renault cars with Euro-4 and even Euro-5 standards.

Catalytic converter is considered by the manufacturers to be a reliable part of any modern car and so they do not provide any certain regulations for its replacement procedure. That is, in their opinion, the life of catalytic convertor should be equal to the life of the entire car. Nevertheless, practice has shown that catalytic converters do not always serve flawlessly.

What may happen to the neutralizer?

  • The first catalytic converter active element malfunction is its reflow, which manifests itself in the form of honeycombs sintering and as a result it becomes much more difficult for the exhaust gases to pass. Usually this happens after the gas temperature exceeds 900 degrees.
  • The second possible scenario is the destruction of a ceramic layer in catalytic converters. In other words, ceramic crumbling.
  • And the third common malfunction is when a catalytic converter is clogged with products of incomplete fuel and oil combustion, which is preventing the car engine from "breathing".

A number of manufacturers use a porous structure instead of a ceramic base. And between car owners this option is considered more reliable.

Honeycombs melting can usually be diagnosed by a drop in engine power - acceleration becomes worse, until the engine stops gaining speed even without a load. The maximum speed becomes lower and lower, and starting the engine, both cold or heated, becomes difficult. Later on it generally ceases to start. In case there is such a malfunction, the Check-Engine indicator lights up, and it's hard not to notice it.

Much more insidious is a malfunction when particles of ceramics begin to crumble from the honeycombs surface. The reason for the ceramic destruction is most often in a poor fuel quality, which burns out at the discharge cycle. And crushing begins in the hottest zone, on the edges of honeycombs, located closer to the engine.

When the engine is running in different modes, a portion of the exhaust gases can be thrown back into engine cylinders. Ceramic dust, which is actually an abrasive, may get with the flow of gases into the cylinder. In this case it will quickly disable the piston group and lead to scuffing on cylinders walls.

However, this phenomenon is dangerous not for all types of engines. We will not even talk about models where the catalytic converter (on the contrary to global trends) is fixed under the bottom of the car, and therefore the harmful particles would have to overcome almost a meter "against the current." Some manufacturers are using correct design solutions and could manage to avoid these problems or to eliminate them in time.

What about the warranty?

The example with the Nissan QR engine is typical. These engines, for example, were installed on the X-Trail first generation (T-30). At a run of no more than 40-60 thousand km, the process that we mentioned above was already starting. Engines were failing due to the increased wear of the cylinders due to the particles of the destroyed ceramic block. But Nissan took the right position on this matter. The block of cylinders with a piston and a short-block were replaced by the warranty and the catalytic converter was replaced with the modern one. At that time the car owners could easily define the new converter from the old one by to the angle of the oxygen sensor inclination. The same phenomenon was encountered by Toyota Camry owners, only there the wear manifested itself later, after about 100 thousand km. And in this case there were owners who have managed to repair their cars using warranty, but there were those who could not make it on time.

Considering this pleasant attitude towards the consumer, KIA is making a sharply negative impression. Service books of cars manufactured by this brand before the beginning of 2016 had an inscription that the warranty obligations for the catalytic converter extend till 1 (!) thousands of kilometers. Roughly speaking, the car owner makes two fuelings, and then "bad Russian gasoline" can damage the catalytic converter, but the company is no longer responsible for this. But since 2016 the catalytic converter warranty has been extended to 150 thousand km.

In the opinion of the author, the catalytic converter warranty should be no less than the duration of the car itself.

Now let's take a closer look at what should and what should not be done by the car owner so the catalytic converter will last longer.

Reasons for the catalytic converter failure:

  1. Poor fuel quality - most often with a low octane rating. The engine control system switches to a later ignition. This causes the mixture to burn out at the outlet while the exhaust gases temperature rises.
  2. Incorrect operation of the ignition system (misfiring). Not burned in one cylinder, the fuel is immediately ignited and burns in the converter.
  3. Catalytic converter mechanical damage. Increased vibration of the power unit and mechanical impacts on the catalytic converter both may lead to the ceramic block crumbling.
  4. Thermal shock. Instantaneous cooling of the incandescent catalytic converter while overcoming the puddle, for example, may cause cracks in the ceramic element.
  5. Incorrect air / fuel mixture composition caused, for example, by a malfunction of the oxygen sensor. The same effect will have unsealed, pouring jets.
  6. Adding additives to gasoline. Cocktails from untested manufacturers or a concentration violation may increase the combustion temperature at the outlet.
  7. The newest engine designs with minimal toxicity are programmed for rapid converter warming. In cold weather, in order to accelerate the warm-up, the engine control units first re-enrich the mixture, which burns out on the surface of the catalytic converter.
  8. In car production history there were frank defects in the catalytic converters design. For example, Suzuki held a campaign for the complete replacement of catalytic converters on SX4 cars.

What if this is the end?

The failed catalytic converter on a car that has no warranty will rarely be replaced. It’s far too expensive. So what could be the right option in this case?

  1. Just knock out the stuffing from the catalytic converter. This requires the control unit reflashing so that it will not be able to recognize signal from the second oxygen sensor, or installing a mechanical or electronic blend. The mechanical one is a bushing with a piece of catalytic converter fixed in it, and the electronic one simply simulates the correct signal of the oxygen sensor.
  2. Remove the filling and install a flame suppressor instead. It is a series of chambers with holes that serve to reduce the gas temperature and pressure. This somewhat reduces the noise and facilitates the operation of other components of the exhaust system. The "brains" of the car have to be deceived, as described above.
  3. Install a universal repair catalytic converter instead of a ceramic block. Most often it has metal basis. The degree of gas neutralizing will be slightly lower, but it’s still better than nothing.