VW fuel-injection systems explained
Differences between Bosch K-Jetronic, KA-Jetronic, KE-Jetronic, Digijet, Digifant and Simos.
From mechanical continuous injection to electronic engine management: a technical overview based on the supplied documents.
K-Jetronic
How it works
Continuous injection: rather than being injected in timed pulses for each cylinder, fuel is delivered continuously ahead of the inlet valves – hence the K, from the German word 'kontinuierlich'.
Air-flow sensor plate: incoming air lifts a mechanical sensor plate in the intake tract.
Fuel distributor: a lever mechanism transfers the plate's movement to a control plunger in the fuel distributor, metering fuel in proportion to the incoming air.
No electronic control: the basic system operates mechanically, without an electronic control unit.
Warm-up regulator: when the engine is cold, the regulator alters control pressure to enrich the mixture.
KA-Jetronic
An extension of K-Jetronic: an electrically operated frequency valve in the control-pressure circuit, commanded using a lambda sensor, allows limited mixture correction for catalytic-converter operation.
KE-Jetronic
Mechanical foundation: like K-Jetronic, it uses an air-flow sensor plate and lever-operated plunger in the fuel distributor to supply fuel continuously to the injectors.
Electronic addition: E stands for electronics. An ECU evaluates signals including the lambda sensor, coolant temperature and the sensor-plate potentiometer.
Electrohydraulic pressure actuator: an electrohydraulic actuator (EHA) on the fuel distributor allows the ECU to alter differential pressure and adjust mixture strength to driving conditions.
Digijet
Fuel injection only: unlike the later Digifant system, Digijet controls fuel injection but not ignition. Ignition advance is controlled separately by the distributor's centrifugal and vacuum mechanisms.
Digifant
The name: the source text derives it from the words 'digital' and 'Elefant' (elephant), reflecting a nickname used by VW developers.
Operation: sensors measure engine speed, temperature and air flow. Using programmed maps, Digifant calculates fuel quantity and ignition timing.
Simos
Successor to Digifant: Simos superseded the earlier Digifant management system from the mid-1990s onwards.
Functions: the system centrally controls fuel injection, ignition timing, idle speed and emissions-related functions, including lambda control and evaporative-emissions management.
Sensor-based operation: the required fuel quantity is calculated from engine load, using inputs such as air-mass flow and engine speed.
Adaptive control: the ECU can adapt to wear and changing operating conditions and may incorporate cylinder-selective knock control.
These are simplified descriptions. Equipment and control strategies vary by vehicle and system version.