Citroën used various systems of two manufacturers, Bosch and Magneti Marelli. All those systems operate on very similar principles so troubleshooting them involves more or less the same steps.
There are two basic categories: fuel injection (EFI) and engine management (EMS). EFI systems, as their name implies, are responsible for the injection of fuel only, the ignition sparks are created using traditional methods (a breakerless distributor). EMS systems, in contrast, govern both fuel injection and ignition themselves.