Peugeot 205 Manual
General informationIgnition system / General information
Electronic breakerless ignition
A number of different breakerless ignition systems are used on 205 models according to engine type and fuel system fitted. Some are simple self-contained systems and some work in conjunction with the fuel system to form an integrated engine management package.
In order that the engine may run correctly it is necessary for an electrical spark to ignite the fuel/air mixture in the combustion chamber at exactly the right moment in relation to engine speed and load.
Basically the ignition system functions as follows. Low tension voltage from the battery is fed to the ignition coil, where it is converted into high tension voltage. The high tension voltage is powerful enough to jump the spark plug gap in the cylinder many times a second under high compression pressure, providing that the ignition system is in good working order.
The distributor contains a reluctor mounted onto its shaft and a magnet and stator fixed to its body. An ignition amplifier unit is mounted either remotely, adjacent to the ignition coil, or on the side of the distributor body.
When the ignition is switched on but the engine is stationary the transistors in the amplifier unit prevent current flowing through the ignition system primary (LT) circuit.
As the crankshaft rotates, the reluctor moves through the magnetic field created by the stator. When the reluctor teeth are in alignment with the stator projections a small AC voltage is created. The amplifier unit uses this voltage to switch the transistors in the unit and complete the ignition system primary (LT) circuit.
As the reluctor teeth move out of alignment with the stator projections the AC voltage changes and the transistors in the amplifier unit are switched again to interrupt the primary (LT) circuit. This causes a high voltage to be induced in the coil secondary (HT) windings which then travels down the HT lead to the distributor and onto the relevant spark plug.
The ignition is advanced and retarded automatically by centrifugal weights and a vacuum capsule or by the engine management electronic control unit to ensure that the spark occurs at the correct instant in relation to engine speed and load.
Static distributorless ignition
A static ignition system is used on models with MMFD Mono-point G5 and G6 engine management systems. The system is integrated with the fuel injection system, and is controlled by the MMFD electronic control unit (ECU). The ECU receives information from various sensors, and using this information, the optimum ignition advance for the prevailing engine conditions is selected from a series of “mapped” values stored in the ECU memory (see Chapter 4B for further information).
The single ignition module replaces the amplifier unit, HT coil and distributor in a conventional system. The ignition module incorporates a double coil, with four high-tension outputs to the spark plugs, which dispenses with the requirement for a conventional distributor and rotor arm.
Each coil is controlled by the MMFD electronic control unit. Each time one of the coil primary circuits is switched, two sparks are provided, one to a cylinder on the compression stroke, and one to a cylinder on the exhaust stroke. The spark to the cylinder on the exhaust stroke is effectively a “wasted spark”, but has no detrimental effect on the performance of the engine.