Peugeot 405 Manual

Ignition system - general information
Ignition system / Ignition system - general information


Breakerless
Electronic ignition system All carburettor models, and models fitted with the Bosch L3.1-Jetronic and Bosch LU2- Jetronic fuel injection systems are equipped with a breakerless electronic ignition system is used. The system comprises solely of the HT ignition coil and a distributor mounted on the left-hand end of the cylinder head and driven by the camshaft. On carburettor models the coil is mounted on a bracket attached to the cylinder block, and on models fitted with L3.1 and LU2 systems it is mounted on the inlet manifold.

The distributor contains a reluctor mounted onto its shaft and a magnet and stator fixed to its body. The ignition amplifier unit is also mounted onto the side of the distributor body.

The system operates as follows.

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.

A TDC sensor is fitted to the rear of the flywheel but the sensor is not part of the ignition system. It is there to be used for diagnostic purposes only.

Integral ignition/
fuel injection system
On fuel-injected models except the L3.1 and LU2 systems, the ignition system is integrated with the fuel injection system to form a combined engine management system under the control of one ECU (See the relevant Part of Chapter 4 for further information).

The Bosch Motronic ML4.1 and Fenix 1B systems retain the distributor cap and rotor arm assembly in order to distribute the spark to the cylinders, together with a conventional ignition coil.

All other models use a static (distributorless) ignition system, consisting only of a four output ignition coil. The ignition coil actually consists of two separate HT coils which supply two cylinders each (one coil supplies cylinders 1 and 4, and the other cylinders 2 and 3). Under the control of the ECU, the ignition coil operates on the wasted spark principle, ie. each spark plug sparks twice for every cycle of the engine, once on the compression stroke and once on the exhaust stroke - the spark on the exhaust stroke has no effect on the running of the engine, and is therefore wasted. The ECU uses its inputs from the various sensors to calculate the required ignition advance setting and coil charging time.

On some models a knock sensor is incorporated into the ignition system. The sensor is mounted onto the cylinder head and prevents the engine pinking under load. The sensor is sensitive to vibration and detects the knocking which occurs when the engine starts to pink (pre-ignite). The knock sensor sends an electrical signal to the ECU which in turn retards the ignition advance setting until the pinking ceases.

Direct ignition system
The ignition system on 1998 cc XU10J4 (16-valve) models is of the direct type. The system components consist of two amplifier modules, four ignition HT coils, and a knock sensor. The ignition system is integrated with the fuel injection system, to form a combined engine management system under the control of one ECU via the ignition amplifier modules.

Each ignition amplifier module operates two HT coils; the ignition HT coils are integral with the plug caps, and are pushed directly onto the spark plugs, one for each plug. This removes the need for any HT leads connecting the coils to the plugs. The ECU uses the inputs from the various sensors to calculate the required ignition advance setting and coil charging time.

The knock sensor is mounted onto the cylinder head, and prevents the engine pinking under load. The sensor detects abnormal vibration, and is thus able to detect the knocking which occurs when the engine starts to pink (pre-ignite). The knock sensor sends an electrical signal to the ECU, which in turn retards the ignition advance setting until the pinking ceases.


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