Engine Ignition System: How Modern Petrol Engines Fire

The ignition system on a modern petrol engine fires the spark plug at precisely the right moment to ignite the fuel-air mixture. Older systems used a distributor — a single coil firing all cylinders via a rotating rotor and cap. Modern systems use coil-on-plug or coil pack designs — a coil per cylinder, eliminating the distributor entirely. Either way, the components: spark plugs, ignition coils, leads (on older designs), and the distributor cap and rotor (older designs).

Coil-on-plug vs distributor

Coil-on-plug: one coil per cylinder, mounted directly on top of each spark plug. ECU fires each coil independently. Failure of one coil affects only one cylinder. Standard on almost all cars 2000 onward.

Distributor systems: one coil for all cylinders, fed through a distributor cap and rotor that routes the spark to each cylinder. Failure of the cap or rotor causes multi-cylinder misfire. Most pre-2000 cars.

What this category covers

Spark plugs, glow plugs, ignition coil packs, ignition leads, distributor caps and rotor arms.

Browse the engine ignition range on the Engine Ignition collection.