General information about the emission control system (BMW 3 Series E46)

1. All engines have a number of devices and functions that are designed to minimize harmful emissions into the atmosphere. The main ones are the engine crankcase ventilation system, the catalytic converter and the fuel vapor management system. In addition, the 4-cylinder engines and the 6-cylinder M52TU engines are also equipped with a secondary air injection system, which helps the catalytic converter to enter working condition faster,

2. Please note: the use of leaded gasoline is not permitted.

Crankcase ventilation control

3. To reduce the emission of unburned hydrocarbons from the crankcase into the atmosphere, the engine is sealed, and the gases that have broken through into the crankcase and oil vapors are removed from it through an oil separator into the intake manifold, from where they enter the cylinders and burn there in the usual way.

4. The pressure in the crankcase is always slightly higher than in the intake manifold, so the gases from the crankcase are sucked into the manifold. If the engine is heavily worn, the gases breaking through into the crankcase have excess pressure and under the influence of this pressure also get into the intake manifold. Thus, the gases will always get into the manifold under any circumstances.

Exhaust gas composition control

5. To reduce harmful components in exhaust gases, all models are equipped with a catalytic converter, which is part of the exhaust system. The system for controlling the composition of the working mixture has feedback through one or two oxygen sensors located in front of and behind the converter. The sensors constantly inform the ECU about the amount of oxygen in the exhaust gases, which allows the mixture composition to be controlled in such a way as to ensure the best conditions for the operation of the converter,



6. The oxygen sensor is equipped with a heating element, which allows the sensor to reach the required temperature more quickly and start working. The tip of the sensor is sensitive to oxygen and, depending on its quantity, sends a voltage of different levels to the ECU. If the working mixture is too rich, the exhaust gases contain little oxygen and the sensor sends a low-level signal to the ECU. When the mixture is lean, the proportion of oxygen in the exhaust gases increases and the sensor sends a high-level signal to the ECU. The best neutralization of all harmful components in the exhaust gases is achieved when the composition of the working mixture corresponds to the chemically necessary fuel-air ratio for complete combustion of the fuel. Such a mixture consists of 14.7 parts air (by weight) and 1 part gasoline (the specified ratio is called stoichiometric). The voltage at the oxygen sensor output changes especially sharply at this point, so the ECU can very accurately regulate the mixture composition by changing the duration of the injector opening pulse.

Fuel vapor management

7. To reduce the possibility of unburned hydrocarbons entering the atmosphere, all models are equipped with a fuel vapor management system. The fuel tank filler neck is hermetically sealed, and fuel vapors from the tank enter the charcoal filter (absorber) located under the bottom at the rear of the car through a ventilation hose. Fuel vapors accumulate in the charcoal filter while the car is parked. When the engine is running, the ECU opens the filter purge valve, through which the accumulated fuel vapors enter the intake manifold and burn in the engine cylinders.



8. To ensure normal engine operation during warm-up and idling, the carbon filter purge valve is closed to prevent over-enrichment of the mixture. The valve opens only when the engine reaches operating temperature and only when operating under load.

Secondary air injection system

9. This system is installed on 4-cylinder engines and M52TU engines. The purpose of the system is to reduce the warm-up time of the catalytic converter. For normal operation, the catalytic converter must have a temperature of at least 300°C. This temperature level is maintained by constantly hot exhaust gases passing through the converter. In order for the converter to reach this temperature level faster, clean air is mixed into the exhaust gases behind the exhaust valves. This oxygen-enriched mixture allows all the fuel that has not had time to burn in the engine cylinders to be burned in the manifold and in the exhaust system. The exhaust gas temperature increases and warms up the converter faster. The system only operates during a cold start (up to 33°C) and switches off after about 2 minutes.