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The K-Jetronic is the first mechanical-hydraulic and continuous fuel injection. It only appeared late in the development of the motor-car because the injection amounts are so small. In addition, the technology delivers the minutest pressure difference valves. Apart from the electronics, it is always regarded as the technically most demanding mixture processing system with good values, particularly with the responding properties of the Otto engine.

Basic Function

Per cylinder, one injector-valve through its own controller, is connected with the fuel distributor. There, a suitable number of pressure difference valves provides for the fuel delivery control. The difference of 0.1 bar, is caused by a spring in the upper chambers, which presses on the steel membrane. All the lower chambers are connected to the system pressure with 4.7 bar.

In the center of the circularly arranged difference valves, a control piston is raised by the air sensor plate working in the vacuum tract according to the amount of intake air. This occurs either by the rising current principle (figure 2), or the air sensor plate is pressed downwards by the falling airflow. In any event, the lever mechanism is so formed that the control piston moves upwards and allows only a 1/10 mm wide slot to open the to single upper chambers.To be able to regulate fuel amounts of e.g., only 5 mm³ per cylinder for two crankshaft rotations, the opening cross section, as well as the pressure difference, are minimised precisely.

Special Function

The mixture enrichment is regulated almost by itself because of the constant oscillating sensor plate. The warm running regulation is somewhat more complicated. If the cold engine has been started by the L-Jetronic with suitable cold starting equipment and additional cold starting valve with a thermo time switch, it needs a richer mixture. for this purpose, a portion of the system pressure, through a throttle, is directed from above, onto the control piston. In a warm engine, this hinders the control piston on its way upwards (normal mixture). However, if the engine is cold, this control pressure of approx. 3.3 bar, is lowered down, depending on the temperature, to as little as 1 bar. Thus, more fuel-flow develops at the same air-transfer rate, providing a richer mixture.

The warming-up controller (figure 5) is responsible for the pressure reduction. A bi-metal with its spring weakens the closing force of a holding valve in the flow-back. This means a shallower pressure gradient to the flow-back, and thus, a lower control pressure. As soon as the ignition is switched on, it is heated and the spring tension decreases. Thus the retaining spring can assert itself more, and provides for an increase in the control pressure. Later, the warm-running compensator receives an additional full-strain membrane with vacuum connection. This lowers the control pressure and provides, through enrichment, for the achievement of the catalogue values.


Vehicles with continuous injection, are especially sensitive to fouling in the fuel-cycle and long down-times. An examination is possible, by bridging the fuel pump relay and injecting the single injectors into small test tubes (max. 10% deviation when the air sensor plate is in the center position).

Exhaust gas decontamination

For foreign countries, a K-Jetronic with Lambda-control, called the KA-Jetronic, is available. 10/09

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