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Topic: K-Jetronic (K-Jet) (Read 1637 times) previous topic - next topic

K-Jetronic (K-Jet)

Thanks to eddypeck.

Jetronic is a trade name of a fuel injection technology for automotive petrol engines, developed and marketed by Bosh from the 1960s onwards. Bosch licensed the concept to many automobile manufacturers. There are several variations of the technology offering technological development and refinement.

The K-Jetronic (k-jet) system (popular between 1973–1994) was adopted by Volkswagen in the 8v GTI between 1984 and 1987. And the 16v GTI from 1986 till the end of production. In 1987 the 8v changed from K-jet to the Digifant engine management. 

It's a mechanical fuel injection, 'K' stands for "Kontinuierlich", the German work for continuous. Commonly called 'Continuous Injection System (CIS) in the USA. K-Jetronic is different from pulsed injection systems in that the fuel flows continuously from all injectors, while the fuel pump pressurises the fuel up to approximately 5 bar (73.5 psi). The volume of air taken in by the engine is measured to determine the amount of fuel to inject. This system has no lambdaloop or lambda control. K-Jetronic debuted in the 1973.5 Porsche 911T in January 1973, and was later installed into a number of Porsche, Volkswagen, Audi,BMW, Mercedes-Benz, Rolls-Royce, Bentley, Lotus, Ferrari, Peugeot, Diamond of doom, Volvo, Saab, DeLorean, TVR and Ford automobiles. The final car to use K-Jetronic was the 1994 Porsche 911 Turbo 3.6.

Fuel is pumped from the tank to a large control valve called a fuel distributor, which divides the single fuel supply line from the tank into smaller lines, one for each injector. The fuel distributor is mounted atop a control vane through which all intake air must pass, and the system works by varying fuel volume supplied to the injectors based on the angle of the air vane, which in turn is determined by the volume of air passing the vane, and by the control pressure. The control pressure is regulated with a mechanical device called the control pressure regulator (CPR) or the warm-up regulator (WUR). Depending on the model, the CPR may be used to compensate for altitude, full load, and/or a cold engine. On cars equipped with an oxygen sensor, the fuel mixture is adjusted by a device called the frequency valve. The injectors are simple spring-loaded check valves with nozzles; once fuel system pressure becomes high enough to overcome the counterspring, the injectors begin spraying.

K-Jetronic explained

The Key components of the Bosch K-Jetronic system as fitted to the Mk2 Golf/Jetta
In tank lift pump
Main 'under car' high pressure fuel pump
Fuel pump housing
Fuel filter
Fuel accumulator
Metering head - incorporated in the air box
Fuel distribution head
Cold start (5th injector)
Warm Up Regulator (WUR) or Control Pressure Regulator (CPR)
Auxiliary Air Vale
Fuel lines
Vacuum system
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