Additional air supply valves of the K-Jetronic system (BMW 5 Series E12)

This valve serves to increase the crankshaft speed during engine warm-up. When starting a cold engine, the additional air supply channel is opened by the rotary valve flap, which moves when the bimetallic spring heats up. As the engine warms up, the additional air supply channel gradually closes.

In addition, the supply of additional air is regulated by the pressure disk of the air quantity meter, the movement of which leads to a corresponding rise of the distribution plunger, which also contributes to an increase in the crankshaft speed (with the throttle valve closed).

When starting a cold engine, the electromagnetic starting injector, controlled by a thermal time relay, sprays an additional amount of fuel into the intake manifold.

Fuel is supplied to the starting injector directly from the distributor under a pressure of approximately 4.7 kg/cm².

The maximum operating time of the injector at a temperature of minus 20°C is 8 s. At a coolant temperature above 15°C, the starting injector does not turn on.

[This article is based on data from the website BMWMan]