From Citroen SM Wiki
Revision as of 10:56, 15 June 2013 by Brodule (talk | contribs)

D-Jetronic was developed by Bosch as early as the sixties. Citroën had already been using it for the DS IE, and launched the SM IE with it in 1972.

The 'D' in D-Jetronic stands for "Drück" and it's a Speed-density system, meaning that no air flow meter is required. Instead a MAP (Manifold Absolute Pressure) sensor is used to measure load. Speed-Density systems are quite common even today.

The ECU is competely analog and is a pretty sturdy unit. Injectors are low impedance, requiring ballast resistors in the ECU.

The D-Jetronic system is good for what it is. The primary issue with the system is that it does not use a lambda sensor, and cannot compensate for wear on the engine and sensors.

Cars after February 15 1973 were fitted with a new and safer two piece fuel rail. Earlier models were fitted with a four piece fuel rail.


  • NEVER start or run the car with the original Bosch 0 280 150 003 injectors. Replace immediately with 0 280 150 043. YOU HAVE BEEN WARNED. The original injectors leak internally, and can lead to catastrophic fire.
  • NEVER run the car with the original external fabric sheath fuel pipe, however good it looks. Replace every piece if present with modern fuel injection piping. YOU HAVE BEEN WARNED.
  • The ECU may go lean when the engine is very hot.
  • A larger/modern alternator (see Alternator) makes the car run much better, even though the fuel computer can operate as low as 5V, as the car will be charge even at idle.
  • Check that the cooling fans have not dropped a magnet internally (e.g. both take the same current). This can be characterised by a sharp crack when they turn on. A failed magnet causes much more current draw, lowering the voltage avalable at idle.

See also