Ignition System: Description and Operation

The ignition system is of inductive type and has no distributor. The six spark plugs are connected to an ignition coil module containing three ignition coils.

Each ignition coil supplies high-tension current to two spark plugs and produces a spark in two cylinders simultaneously. These two cylinders have the same crankshaft order and the pistons will therefore be just before top dead centre. Since one of the pistons is on its exhaust stroke and the other on its compression stroke, only one of the sparks will be of any use.

The ignition coil module is supplied with current (+15 circuit) and has three terminals connected to the control module.

Ignition is activated as soon as the control module receives pulses from the crankshaft position sensor. The control module connections are grounded and then broken in accordance with the engine's firing order:

^ the primary winding for cylinders 1-4 is connected to pin 49 of the control module
^ the primary winding for cylinders 2-5 is connected to pin 50 of the control module
^ the primary winding for cylinders 3-6 is connected to pin 51 of the control module

Since the ignition system is inductive, the spark is generated when the circuit is broken.

Since the two poles for each secondary winding are each connected to a spark plug, the circuit through the two spark plugs is closed. through the engine block. In the event of a break (no Continuity) in the circuit to a spark plug a spark will still be produced by the other spark plug in the same circuit since the ignition coil and the possibly loose high-tension cable act as a capacitor relative to ground and close the circuit.





Ignition Control
On starting, the ignition timing is dependent on coolant temperature and starting rpm. A typical figure for a hot engine is 15.75° BTDC.

At idling speed the timing is dependent on engine load and rpm. Atypical figure for a hot engine is 9.75° BTDC.

The ignition timing is dependent on engine load and speed when the car is being driven, just as it is when the engine is running at idling speed.

When the engine is laboring under a heavy load, a special timing angle matrix is used to reduce the risk of knocking.

The cam angle varies with engine rpm so that the highest possible ignition energy is always obtained with the least possible generation of heat in the ignition coil and output stage of the control module.

If engine speed drops, as might occur due to the effect of power steering, the ignition will be advanced by a maximum of 4.5° to increase engine, torque and so bring engine rpm up to what it was before.

Similarly, the ignition will be retarded by a maximum of 3.0° if engine rpm increases. Ignition timing control at idling rpm takes care of rapid changes in engine idling speed.





Ignition Timing
Ignition timing, is calculated by the control module chiefly on the basis of the following information:
^ engine load
^ engine speed
^ knocking, if any
^ throttle position (idling only).

The crankshaft position sensor consists of an inductive sensor mounted in the crankcase wall of the engine. The rotor is a slotted ring with 58 ribs mounted on the rear counterweight of the crankshaft.