Digijet is the name for an engine control unit series from the Volkswagen group. The word Digijet is made up of "digital injection" and describes a digital injection system. The Digijet engine control unit series was produced by Bosch and later also by Motor Vehicle Electronics Nuremberg (KEN).
The Digijet is an electronically controlled injection with programmed injection map with overrun cut-off , lambda control , cold start, warm-up and full load enrichment. The construction of the Digijet corresponds to the L-Jetronic . The injection valves are activated simultaneously and inject the fuel into the intake manifold in front of the intake valves . When starting up until a minimum engine speed is reached, four injections per work cycle, then twice per work cycle. The higher injection frequency at the start is intended to improve the preparation of the mixture. In all Digijet versions, the ignition timing is controlled mechanically by the vacuum unit on the distributor or by a centrifugal actuator in the distributor, sometimes also by both together. In addition, there is the "digital idling stabilization", which keeps the idling speed constant by changing the ignition angle.
The engine control unit does not have a fault memory. A rudimentary diagnosis is only available for a few variants.
If individual sensors fail, standard values are assumed, so that in most cases it is still possible to drive to the workshop (emergency operation).
- The injection valves are opened longer by the control unit in order to enrich the mixture. The opening time decreases as the temperature rises.
- The lambda control is deactivated.
- The auxiliary air slide or an idle speed control increase the idle speed.
- In the warm-up phase, idling is stabilized by the idling adjuster / additional air slide.
- The lambda control is switched on from a certain cooling water temperature.
- The throttle valve switch sends information (closed when idling and full load) to the control unit. The distinction between "idle or full load" is made based on the amount of air passed through. At full load, the mixture is enriched to around 3% CO (maximum output with slightly reduced NO x emissions); at idle, the overrun cut-off is activated above a minimum speed.
A rapid increase in the amount of air also leads to a short-term enrichment similar to the acceleration pump of the classic carburetor.
Change in intake air temperature
- Detection via the intake air temperature resistance. The control unit reacts by changing the injection quantity.
- The control unit receives the speed information from the distributor and reduces the injection quantity between 6400 min −1 and 6500 min −1 .
- Detection via speed , throttle valve switch and air flow meter; the control device stops the injection at the engine is warm, the accelerator pedal released and above 1500 min -1 .
- Detection via speed , throttle valve switch and air flow meter; the control unit also increases the amount of fuel injected. The lambda control is switched off here.
- A lambda probe detects a rich or lean mixture, and the injection quantity is adjusted accordingly.
The Digijet was first installed in the VW T3 with a water boxer engine with the engine code DH (USA), GW (Europe) and DJ. It was later used in the Jetta , Golf , Polo and Polo Coupe models . There in the in-line four-cylinder engine with the engine code NZ. In the case of the water boxer engines, the idle speed is partly regulated by a separate control unit and a flapper plate actuator as a bypass to the throttle valve in order to prevent idle fluctuations and to stabilize the idle speed when the air conditioning is switched on or the steering is turned strongly. Otherwise there was only one additional air valve that increases the idling time (electric heating) and engine temperature during the cold start and the warm-up phase. All variants also have an idle stabilization via the ignition point.
Overview of the Digijet variants
|model||Displacement||design type||cylinder||power||MKB||construction time|
|1.9 l||1888 cc||WBX||4th||60 kW (82 PS)||DH||1982-1985|
|1.9 l||1888 cc||WBX||4th||66 kW (90 PS)||GW||1983-1985|
|2.1 l||2081 cc||WBX||4th||82 kW (112 hp)||DJ||1984-1989|
|1.3 l||1272 cc||line||4th||40 kW (55 PS)||NZ||1987-1992|
- Dieter Korp: now I'm helping myself, Volume 111, Motorbuch Verlag, Stuttgart, 2010, ISBN 3-613-01031-3
- Dieter Korp: now I help myself, Volume 139 Motorbuch Verlag, Stuttgart, 1999, ISBN 3-613-01337-1
- Hans-Rüdiger Etzold: This is how it's done, Volume 43 Delius, Klasing, Bielefeld, 2000, ISBN 3-7688-0473-9