Operating principle of the Motronic DME M1.7 system (four-cylinder engine) (BMW 3 Series E36)

Fuel is supplied by an electric fuel pump from the fuel tank through the fuel filter to the distribution pipe and then to the valve injectors. A pressure regulator in the distribution pipe ensures a constant pressure of 3.0 bar (320i from January 1995, 325i: 3.5 bar). The injectors are electrically controlled and perform pulse fuel injection. The injectors have semi-sequential control, i.e. during one revolution of the crankshaft, simultaneous injection is performed by two injectors, namely alternately by injectors of cylinders 1-3 or by injectors of cylinders 2-4.

Air is sucked in by the engine through the air filter and air intake pipe and is measured by the air flow meter. The air flow meter housing contains a flap that is deflected by the air passing through it at a certain angle. The angular position of the flap serves as a measure of the amount of air passing through. Information about the amount of air passing through is transmitted to the control unit from the potentiometer.

The control unit regulates the injection time and thus the amount of fuel injected according to the measured air mass. With a longer opening time of the injector, more fuel can be injected. Additional sensitive elements and sensors ensure that the required amount of fuel is supplied even in extreme driving situations.



The throttle switch is located directly on the throttle axis. It sends signals to the control unit about the throttle position in idle mode and the full load position. This primarily controls the forced running mode: as long as the throttle switch contact is closed and at the same time the engine speed exceeds a certain value, the control unit blocks the fuel supply to the engine.



The fuel pump relay is located in the relay box in the left rear of the engine compartment. It supplies power to the fuel pump. When the pulses from the speed sensor stop coming in with the ignition on (when the engine stalls) the control circuit interrupts the power supply.

The current position of the engine crankshaft and the number of revolutions are determined by 2 inductive sensors: The speed and reference mark sensor is located in the mount on the crankshaft belt pulley, the cylinder recognition sensor is an inductive loop on the ignition wire of cylinder 4.

Lambda probe (oxygen sensor) measures the oxygen content in the exhaust gas flow on vehicles equipped with a regulated catalytic converter and transmits a corresponding electrical signal to the control unit. Based on this information, the control unit changes the composition of the intake air-fuel mixture to ensure optimal combustion of the exhaust gases in the catalytic converter.

The idle speed controller regulates the amount of air in the idle mode in the throttle valve area. This ensures a stable speed regardless of whether additional consumers such as the power steering or the air conditioning compressor are connected. The idle speed controller is controlled by the electronic control unit of the fuel injection system.

The coolant temperature sensor measures engine temperature, which has a major impact on fuel consumption.

The activated carbon container accumulates fuel vapors from the fuel tank. When the engine is running, these vapors are supplied in portions through the fuel tank ventilation valve to the engine, thereby reducing the emission of harmful substances and saving fuel.