System Description

Fig. 1 LH-Jetronic II fuel injection system:

This system is an electronic system with one injector per cylinder. This is a second generation system which is similar to the LH-Jetronic I system used on earlier models (to 1982). The LH-Jetronic II system can be identified by a throttle position sensor mounted to the throttle housing (which can not be found on the LH-Jetronic I injection). This system consists of a control unit which receives information from various sensors, then uses this information to control the quantity of fuel injected by varying the injection duration. The control unit also regulates the idle speed by varying the opening of the air control valve.
The LH is an abbreviation for the German equivalent of hot air wire. This name is derived from the fact that engine intake air flow is measured by an air mass meter consisting of an electrically heated wire. This wire is cooled by intake air flow. The control unit constantly regulates the wire heating current to keep the wire at a constant temperature.
Heating current is a measure of intake air mass. Because intake air mass is measured, the system is not affected by ambient air pressure or temperature.

The tank pump, pumps fuel from the tank to the main fuel pump and maintains pressure in the fuel line to the main pump. This effectively eliminates vapor lock. The fuel pump supplies the system with fuel and builds up line pressure.
The fuel filter effectively eliminates impurities before they reach components that they can clog or damage. The line pressure regulator senses intake manifold pressure. It regulates fuel pressure to a constant level above intake manifold pressure. The fuel injectors inject the fuel. The injection duration is regulated by the control unit.