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) 
Analog fuel injection. The 'D' is an abbreviation from German: "Druck", which means pressure. The depression (vacuum) is measured using a pressure sensor located in the intake manifold, in order to calculate the duration of the fuel injection pulses. Originally, this system was just called Jetronic, but the name D-Jetronic was later created as a retronym to distinguish it from the newer versions.
K-Jetronic (1973–1994) 
Mechanical fuel injection. The 'K' stands for German: "Kontinuierlich", meaning continuous. This 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 (72.5 psi). The air that is taken in is also weighed - to determine the amount of fuel to inject. Commonly called 'Continuous Injection System' (CIS) in the USA. 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 and Ford automobiles. The final car to use K-Jetronic was the 1994 Porsche 911 Turbo 3.6.
Gasoline is pumped from the fuel tank to a large control valve called a fuel distributor, which separates the single fuel supply pipe from the tank into smaller pipes, 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 flowrate of air past 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 (Lambda) 
A variant of K-Jetronic with closed-loop lambda control, also named Ku-jetronic, the letter u denominates the USA. The system was developed to comply with Californian exhaust emission regulations, and later replaced by KE-Jetronic. First introduced in the Volvo 265 in 1976.
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. Commonly known as 'CIS-E' in the USA. The later KE3 (CIS-E III) variant features knock sensing capabilities.
L-Jetronic (1974–1989) 
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 movable vane (indicating engine load) known as the mass air flow sensor (MAF) — referred to in German documentation as the LuftMassenMesser 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.
L-Jetronic was used heavily in 1980s-era European cars, 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. 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) 
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 AFM 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 AFM.
LU2-Jetronic (1983–1991) 
The same as LE2-Jetronic, but with closed-loop lambda control. Initially designed for the US market.
LH-Jetronic (1982–1998) 
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; incincluding 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.
Mono-Jetronic (1988–1995) 
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.
See also 
- History of the D-Jetronic System
- Volvo enthusiasts. The site mostly focuses on 240-series cars with the Bosch K-Jet fuel injection systems