Under the adjustable mixture preparation device in technology is meant a carburetor or injection system, where the proportion of air and fuel can constantly change depending on the parameters of movement and the oxygen content in the exhaust gases. A conventional carburetor does not provide this, since it does not have an appropriate control unit. For this reason, either a carburetor with an electronic control system or a fuel injection system is installed.
The mixture preparation device receives control commands from a lambda probe located in front of the catalyst or in the exhaust manifold, where it flows around the exhaust gases. The lambda probe is an electrical measuring sensor that detects the content of residual oxygen in the exhaust gases, converts it into electrical voltage and thus allows you to adjust the composition of the air-fuel mixture. In a fraction of a second, information about the oxygen content is transmitted from the lambda probe to the control unit of the mixture preparation device, which ensures constant regulation of its composition. This is necessary, on the one hand, because the operating modes are constantly changing (idle, full throttle), and on the other hand, also because the afterburning of the fuel in the catalyst occurs only when the exhaust gases contain a sufficient proportion of gasoline.
Thus, in order for the afterburning of fuel to occur in the catalyst at temperatures of 300-800°C, its proportion in the air-fuel mixture must be higher than is required for clean combustion. Thus, when operating a controlled catalyst, an increase in fuel consumption of about 5 percent should be expected.
The catalytic converter is located in place of the pre-muffler under the bottom of the car. The catalyst consists of a honeycomb ceramic monolith plated with platinum or rhodium. Elastic and heat-resistant wire cloth is used to retain the shock-sensitive body of the catalyst.
The catalyst for conventional use is a so-called 3-way catalyst. This means that in such a catalyst, under lambda control, carbon monoxide is simultaneously oxidized (SO) and hydrocarbons (PC), as well as a decrease in nitrogen oxides (Nox).
Operation of vehicles with a catalyst
To avoid damage to the lambda probe and catalytic converter, the following instructions must be observed:
- Refuel with unleaded gasoline only.
- Refuel at least 2 times with unleaded fuel before installing the catalytic converter. In addition, on engines that require supergas, the ignition should be set to a later one, since unleaded supergas has an octane rating of only 95. How many degrees to change the ignition depends on the model.
- Do not start the engine by towing or «with a push». Unburned fuel, when ignited in the catalyst, will cause it to overheat. When the battery is dead, start the engine from the battery of another car.
- Avoid frequent starts of a cold engine in a row. In this case, unburned fuel accumulates in the catalyst, when it is heated, its impact combustion occurs and the catalyst fails.
- If it is difficult to start the engine, do not turn on the starter for a long time unnecessarily. When the starter is running, fuel is constantly injected. Determine and eliminate the source of the problem.
- If a misfire occurs, remove the fuel pump relay connector before determining the cause. This prevents fuel injection when starting the engine. The fuel pump relay is located at the foot of the front passenger in front of the A-pillar under the side trim.
- Do not test for spark with spark plug tips removed.
- Cannot compare cylinders (balance test) by turning off the ignition of one of the cylinders. When the ignition of one of the cylinders is turned off - even with the help of an engine tester - unburned fuel enters the catalyst.
- In the event of ignition failures, avoid running the engine at high speeds and repair the fault immediately.
- Install only spark plugs recommended for vehicles with a catalytic converter.