L-Jetronic fuel injection system
The Bosch L-Jetronic fuel injection system was used on most E28 models ("old style"). This electronic fuel injection system uses one solenoid injector per cylinder. The system is controlled by an Electronic Control Unit (ECU), which processes information received from various sensors, and then produces an accurate fuel dosage for the cylinders by adjusting the open state of the injector. An electric fuel pump delivers high pressure fuel to the injectors through the fuel lines and an in-line filter. The pressure regulator ensures that the fuel is supplied at the optimum pressure, allowing the pressure to rise and fall depending on engine speed and load. All excess fuel is returned to the fuel tank via a separate line.
A sensor in the air intake duct continuously measures the amount of incoming air, and the ECU regulates the fuel mixture to obtain the optimum air/fuel ratio.
Other components included in the system are the throttle valve (which controls the flow of air), coolant temperature sensor, throttle position sensor, idle speed control valve (which, to stabilize the idle speed, removes air, bypassing the throttle valve) and associated relays and fuses.
Motronic fuel injection system
The Motronic system combines L-Jetronic fuel injection system control with ignition timing, idle speed and exhaust control in one unit.
The fuel injection and idle control functions are similar to those described above for the L-Jetronic system. For more information about the Motronic system, please refer to the Head Engine management and emission control systems.
An oxygen sensor on later models with a catalytic converter is installed in the exhaust system. This sensor continuously measures the oxygen concentration in the exhaust gases. This information is used by the ECU to adjust injection timing, allowing the fuel mixture to be set for optimum converter efficiency and minimum emissions.