An adjustable carburetor is a carburetor or fuel injection system in which the fuel-to-air ratio can be constantly changed depending on the driving conditions and the oxygen content of the exhaust gases. This cannot be done with a traditional carburetor, as it is not equipped with a corresponding control unit. For this reason, either an electronically adjustable carburetor or a fuel injection system is used.
The carburetor receives control commands from the oxygen sensor, which is installed in the exhaust pipe before the catalytic converter or in the exhaust manifold and is washed by the exhaust gas flow here. The oxygen sensor is a sensitive element and signals the residual oxygen content in the exhaust gases by means of voltage fluctuations and helps to issue a conclusion on the composition of the fuel-air mixture. In a fraction of a second, the oxygen sensor can transmit the corresponding electrical signals to the carburetor control unit and, thanks to this, the fuel-air ratio is constantly changing. On the one hand, this is necessary, since in any case, the operating conditions are constantly changing (idle speed, full throttle opening), and, on the other hand, also because only in this case does afterburning occur on the catalytic converter, since there is still a sufficient proportion of gasoline in the exhaust gases of the engine.
Therefore, in order for afterburning to occur at all on the catalyst at temperatures from 300 to 800°C, the combustible mixture must have a higher percentage of fuel than would be required for clean combustion. Thus, when using a catalyst, it is necessary to take into account increased fuel consumption, reaching from one to five percent.
The catalytic converter is installed under the base of the car body instead of an additional muffler. The catalytic converter consists of a porous ceramic monolith coated with a layer of platinum or rhodium. An elastic and heat-resistant metal fabric is used to install the shock-sensitive ceramic body.
In this case, we are talking about the so-called three-functional catalyst. This means that on this catalyst, based on the data received from the oxygen sensor, the oxidation of carbon monoxide (CO) and hydrocarbons (HC) to CO₂ and H2O is carried out, as well as the simultaneous reduction of nitrogen oxides (NOx) to nitrogen.
Maintenance of vehicles equipped with a catalytic converter
To avoid damage to the oxygen sensor and catalytic converter, be sure to follow these instructions:
- Always refuel your vehicle with unleaded gasoline. If you accidentally fill up with leaded gasoline, you must replace the exhaust pipe before the catalytic converter, as well as the catalytic converter. Before installing new catalytic converter parts, you must drive out at least two fuel tanks filled with unleaded gasoline. Pushing or towing the engine can only be done if the engine starts immediately. Unburned fuel can cause the catalytic converter to overheat and thus be destroyed when ignited. Use a starter starter from an auxiliary battery.
- Frequent, consecutive cold engine starts should be avoided. In this case, unburned fuel accumulates on the catalytic converter, which suddenly ignites when heated, causing damage to the catalytic converter.
- If you have difficulty starting the engine, do not press the starter for a long time. Fuel is continuously injected during starting. Determine and eliminate the cause of the malfunction.
- Use only approved Mercedes spark plugs.
- Do not perform a spark test on the spark plug wire ends.
- If spark misfires are observed, avoid high engine speeds and promptly correct the defect.
- Do not park the vehicle over dry leaves or grass. The exhaust system becomes very hot in the catalytic converter area and emits residual heat even after the engine has stopped.
- When filling or topping up engine oil, pay special attention to the fact that the maximum mark on the oil level indicator is never exceeded. Otherwise, excess oil due to incomplete combustion gets onto the catalyst and can damage the noble metal or completely destroy the catalyst.