Composite ignition system (ignition/fuel system) (Peugeot 405)

On all models except L3.1 and LU2, the ignition system is integrated with the fuel injection system and is controlled by a single ECU.

Bosch Motronic ML4. l and Fenix IB systems have a distributor cap and rotor to distribute the ignition spark to the cylinders (together with a conventional ignition coil).

All other models use an ignition system consisting of only two ignition coils. The ignition coil actually consists of two separate windings that supply spark to two cylinders each (one to cylinders 1 and 4, and the other to cylinders 2 and 3). An ignition pulse is sent to two spark plugs at once for each engine cycle, one on the compression stroke and one on the exhaust stroke - the spark on the exhaust stroke has no effect on the engine's operation, so it is wasted. The ECU uses inputs from various sensors to calculate the required ignition timing and the time it takes for the energy to build up in the ignition coil.

On some models, the knock sensor is integrated into the ignition system. The sensor is mounted on the cylinder head and prevents detonation in the cylinders under load. The sensor is sensitive to vibration and detects detonation, which occurs when the fuel mixture in the cylinders burns with detonation. The knock sensor sends an electrical signal to the ECU, which in turn reduces the ignition timing until detonation stops.