K-Jetronic

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

D-Jetronic (1967–1979)

Analogue fuel injection, 'D' is from german: "Druck" meaning pressure. Inlet manifold vacuum is measured using a pressure sensor located in, or connected to the intake manifold, in order to calculate the duration of fuel injection pulses. Originally, this system was called Jetronic, but the name D-Jetronic was later created as a retronym to distinguish it from subsequent Jetronic iterations.

D-Jetronic was essentially a further refinement of the Electrojector fuel delivery system developed by the Bendix Corporation in the late 1950s. Rather than choosing to eradicate the various reliability issues with the Electrojector system, Bendix instead licensed the design to Bosch. With the role of the Bendix system being largely forgotten D-Jetronic became known as the first widely successful precursor of modern electronic common rail systems; it had constant pressure fuel delivery to the injectors and pulsed injections, albeit grouped (2 groups of injectors pulsed together) rather than sequential (individual injector pulses) as on later systems.

As in the Electrojector system, D-Jetronic used analogue circuitry, with no microprocessor nor digital logic, the ECU used about 25 transistors to perform all of the processing. Two important factors that led to the ultimate failure of the Electrojector system: the use of paper-wrapped capacitors unsuited to heat-cycling and amplitude modulation (AM radio) signals to control the injectors were superseded. The still present lack of processing power and the unavailability of solid-state sensors meant that the vacuum sensor was a rather expensive precision instrument, rather like a barometer, with brass bellows inside to measure the manifold pressure.

Although conceptually similar to most later systems with individual electrically controlled injectors per cylinder, and pulse-width modulated fuel delivery, the fuel pressure was not modulated by manifold pressure, and the injectors were fired only once per 2 revolutions on the engine (with half of the injectors being fired each revolution).

The system was last used (with a Lucas designed timing mechanism and Lucas labels super-imposed on some components) on the Jaguar V12 engine ( XJ12 and XJ-S) from 1975 until 1979.

K-Jetronic (1973–1994)

Mechanical fuel injection, 'K' stands for german: "Kontinuierlich", meaning ''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 lambda loop 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, Nissan, Renault, Volvo, Saab, 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 a moving vane in the air flow meter, 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. 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 (Lambda)

First introduced in the Volvo 265 in 1976 and later used in the DeLorean in 1981. A variant of K-Jetronic with closed-loop lambda control, also named Ku-Jetronic, the letter u denominating USA. The system was developed to comply with U.S.A. state of California's California Air Resources Board exhaust emission regulations, and later replaced by KE-Jetronic.

KE-Jetronic (1985–1993)

Electronically controlled mechanical fuel injection. The engine control unit (ECU) may be either analog or digital, and the system may or may not have closed-loop lambda control. The system is based on the K-Jetronic mechanical system, with the addition of an electro-hydraulic actuator, essentially a fuel injector inline with the fuel return. Instead of injecting fuel into the intake, this injector allows fuel to bypass the fuel distributor, which varies the fuel pressure supplied to the mechanical injection components based on several inputs (en