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What is the ignition/what does it do?

The ignition system varies; depending on the year of manufacture and make, model and engine type. The system which is switched on from the ignition key allows the delivery of the electrical power to enable the firing and control of the combustion engine.

Getting into the details of the ignition

In older petrol engines with carburation fuel delivery, the firing sequence is initiated via an electrical coil.  This coil increases the electrical power to the high voltage charge required to enable an arc on the gap of each spark plug in sequential timing for each cylinder, through a rotor arm inside a distributor. Inside the distributor cap the mechanically driven rotor arm spins picking up power from a sprung loaded carbon tip onto the top center of the rotor this power travels along the arm making a connection with contacts around the inside of the cap. As the engine increases in speed the rotor spins faster distributing an electrical pulse to each contact for each cylinder. The charge travels down each cable to each spark plug in turn causing the combustion of the fuel mixture which has been delivered in each piston. Spares for these older types include high tension cables (HT), ignition coils. distributor caps, and rotor arms.

In more modern petrol driven cars, the fuel is delivered by direct fuel injection the system is controlled electronically with various components which control fuel delivery, composition and firing sequences. The distributor is no longer used as individual coils are used for each spark plug and cylinder positioned in close proximity to each spark plug. This has done away with the distributor, the high voltage cabling and a much better delivery of the power to each spark plug is achieved, giving better performance and reliability. On some engines there is one coil supplying a charge for each two cylinders. The spares include various electronic components depending on make, model and engine type, such as ignition coil module, ignition control unit, ignition amplifier etc. In diesel driven engines  there is no spark involved as the combustion takes place through compression of the fuel/air mixture in the firing chamber.There are however glow plugs which ensure the correct temperature of the gases to aid combustion. Spares for diesel engine ignition include  the cold start advance system.

What if something goes wrong with the ignition?

All types of engines are activated via an ignition key which fits a key barrel multi switch on the steering column.This is both mechanical for locking the steering and electronic for turning on power to all electrical systems and activating the starter motor. This barrel can, over a long period, can wear out and need replacing.