An adjustable mixture former is a carburetor or injection device in which the fuel-air ratio can be changed depending on the vehicle's condition and the oxygen concentration in the exhaust gases. This cannot be achieved in a conventional carburetor, since it does not have a corresponding control unit. Therefore, in this case, either an electronically controlled carburetor or an injection system is used.
The control signals for the mixing unit come from the lambda probe, which is located in front of the catalytic converter or in the exhaust manifold and exhaust gas washer. The lambda probe is an electrical sensor that measures the concentration of oxygen contained in the exhaust gases and transmits a signal to the control unit in the form of a certain voltage level. In accordance with this signal, the control unit affects the ratio of the components of the fuel mixture. On the one hand, this is necessary due to a change in the engine operating mode (idle, full throttle), on the other hand, a certain ratio is necessary to ensure the afterburning of exhaust gases in the catalyst.
In order for the afterburning of exhaust gases to occur in the catalyst at a temperature of 300-800°C, the fuel mixture must have more fuel than is necessary for clean combustion of the mixture in the cylinder. As a result, engines equipped with a catalyst have a 5% higher fuel consumption.
The catalytic converter is located in place of the additional muffler under the car's sump. The catalytic converter is a monolithic ceramic honeycomb structure coated with platinum or rhodium. An elastic and temperature-resistant wire mesh is used to attach the impact-sensitive ceramic housing.
The catalysts currently used are so-called triple catalysts. This means that in such a catalyst, three processes are simultaneously regulated by feedback on exhaust gases: oxidation of carbon monoxide (CO) and hydrocarbons (HC), as well as reduction of nitrogen oxide (NOx).
Rules for handling vehicles equipped with a catalytic converter
To avoid damage to the lambda probe and catalytic converter, it is essential to follow these recommendations:
Use unleaded petrol only.
If the car is additionally equipped with a catalytic converter, at least 2 full fills of unleaded gasoline are required before installation. In addition, for engines requiring the use of super gasoline, the ignition timing should be adjusted in the "later" direction, since the proposed unleaded super gasoline has a lower octane number (ROZ 95). The ignition offset angle depends on the model.
Starting the engine by pushing or towing the vehicle is not allowed. Unburned fuel may ignite and cause the catalytic converter to overheat and be destroyed. For this purpose, starting the engine from an external source is necessary.
It is necessary to exclude frequent cold starts one after another. Otherwise, unburned fuel accumulates in the catalyst, which after the engine warms up, burns explosively, destroying the catalyst.
If you have difficulty starting the engine, do not press the starter for too long, as this will cause unburned fuel to accumulate. It is necessary to find the cause of the poor engine start.
If ignition problems occur, remove the fuel pump or fuel injection control relay until the fault is found. This will prevent fuel injection during start-up.
Do not perform a spark test with the ignition plugs removed.
You cannot check for ignition in individual cylinders by disconnecting the tips. When the ignition of any of the cylinders is disconnected, unburned fuel gets into the catalyst.
If ignition failures occur, it is necessary to identify and establish their cause immediately, but without increasing the engine speed.
[Material republished from the website «AUDImanual»]