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Jetronic is a trade name of a fuel 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 (1967–1976)[edit]

Analog fuel injection, 'D' is from German: "Druck" meaning pressure. Inlet manifold depression (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 newer versions.

D-Jetronic was a precursor of modern common rail systems as 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.

K-Jetronic (1973–1994)[edit]

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, Renault, 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 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)[edit]

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. First introduced in the Volvo 265 in 1976.

KE-Jetronic (1985–1993)[edit]

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 (engine speed, air pressure, coolant temperature, throttle position, lambda etc.) via the ECU. With the electronics disconnected, this system will operate as a K-Jetronic system.[1]

Commonly known as 'CIS-E' in the USA. The later KE3 (CIS-E III) variant features knock sensing capabilities.

L-Jetronic (1974–1989)[edit]

Analog fuel injection. L-Jetronic was often called Air-Flow Controlled (AFC) injection to further separate it from the pressure-controlled D-Jetronic — with the 'L' in its name derived from German: 'luft', meaning 'air'. In the system, air flow into the engine is measured by a moving vane (indicating engine load) known as the volume air flow sensor (VAF) — referred to in German documentation as the LuftMengenMesser or LMM. L-Jetronic used custom-designed integrated circuits, resulting in a simpler and more reliable engine control unit (ECU) than the D-Jetronic's.[2]

L-Jetronic was used heavily in 1980s-era European cars,[3] as well as BMW K-Series motorcycles. Licensing some of Bosch's L-Jetronic concepts and technologies, Lucas, Hitachi Automotive Products, NipponDenso, and others produced similar fuel injection systems for Asian car manufacturers. L-Jetronic manufactured under license by Japan Electronic Control Systems was fitted to the 1980 Kawasaki Z1000-H1, the world's first production fuel injected motorcycle. Despite physical similarity between L-Jetronic components and those produced under license by other manufacturers, the non-Bosch systems should not be called L-Jetronic, and the parts are usually incompatible.

LE1-Jetronic, LE2-Jetronic, LE3-Jetronic (1981–1991)[edit]

This is a simplified and more modern variant of L-Jetronic. The ECU was much cheaper to produce due to more modern components, and was more standardised than the L-Jetronic ECUs. The connections between mass airflow meter and ECU are simplified. Three variants of LE-Jetronic exist: LE1, the initial version. LE2 (1984–), featured cold start functionality integrated in the ECU, which does not require the cold start injector and thermo time switch used by older systems. LE3 (1989–), featuring miniaturised ECU with hybrid technology, integrated into the junction box of the mass airflow meter.

LU1-Jetronic, LU2-Jetronic (1983–1991)[edit]

The same as LE1-Jetronic and LE2-Jetronic respectively, but with closed-loop lambda control. Initially designed for the US market.

LH-Jetronic (1982–1998)[edit]

Digital fuel injection, introduced for California bound 1982 Volvo 240 models. The 'LH' stands for German: "Luftmasse-Hitzdraht" - the hotwire anemometer technology used to determine the mass of air into the engine. This air mass meter is called HLM2 (Hitzdraht-LuftMassenmesser 2) by Bosch. The LH-Jetronic was mostly used by Scandinavian car manufacturers, and by sports and luxury cars produced in small quantities, such as Porsche 928. The most common variants are LH 2.2, which uses an Intel 8049 (MCS-48) microcontroller, and usually a 4 kB programme memory, and LH 2.4, which uses a Siemens 80535 microcontroller (a variant of Intel's 8051/MCS-51 architecture) and 32 kB programme memory based on the 27C256 chip. LH-Jetronic 2.4 has adaptive lambda control, and support for a variety of advanced features; including fuel enrichment based on exhaust gas temperature (ex. Volvo B204GT/B204FT engines). Some later (post-1995) versions contain hardware support for first generation diagnostics according to ISO 9141 (a.k.a. OBD-II) and immobiliser functions.[citation needed]

Mono-Jetronic (1988–1995)[edit]

Digital fuel injection. This system features one centrally positioned fuel injection nozzle. In the US, this kind of single-point injection was marketed as 'throttle body injection' (TBI, by GM), or 'central fuel injection' (CFI, by Ford).

Mono-Jetronic is different from all other known single-point systems, in that it only relies on a throttle position sensor for judging the engine load. There are no sensors for air flow, or intake manifold vacuum. Mono-Jetronic always had adaptive closed-loop lambda control, and due to the simple engine load sensing, it is heavily dependent on the lambda sensor for correct functioning.

The ECU uses an Intel 8051 microcontroller, usually with 16 kiB of program memory and without advanced on-board diagnostics (OBD-II) became a requirement in model-year 1996.)

See also[edit]


  1. ^ Robert Bosch GmbH (1985). Electronically Controlled Gasoline Fuel-Injected System with Lambda Closed-Loop Control - KE-Jetronic.
  2. ^ Baggeroer, Artgur B. L-Jetronic fuel injection. July 1985: 43+. General OneFile. Web. 23 July 2012.
  3. ^ Lee Thompson, John De Armond (22 June 1993). "L-Jetronic" (archived usenet message). Retrieved 17 November 2009. 

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