Spark plugs are used by your vehicle's ignition system to generate the sparks used to ignite the air/fuel mixture in a petrol engine. Diesel engines don’t have an ignition system and instead use glow plugs.
The ignition coilpack transforms the low voltage electricity from the battery into high-voltage electricity, which is sent along the HT (High Tension) leads to the spark plugs.
The spark plugs are screwed into the cylinder head, and produce sparks inside the combustion chambers.
Spark plug: what does it do?
Spark plugs are fitted to petrol engines, and their job is to ignite the air/fuel mixture in the cylinders at the correct instant.
When the ignition system sends a voltage down the HT lead to the spark plug, the high voltage causes a spark to jump between the spark plug centre electrode and the earth electrode(s).
A typical spark plug: NGK ignites the explosive air/fuel mixture, which expands, pushing the piston down the cylinder.
The spark plug gap, which is the space between the earth electrode(s) and the centre electrode, can be adjusted to suit a particular engine, but often this is set specifically for your vehicle's engine. Check before you start changing it.
The size of the gap is very important because it controls the way the air/fuel mixture burns. Some spark plugs have more than one earth electrode.
Bad spark plug symptoms
Spark plugs should last for 60,000 miles or more. Modern ones are made of ceramic and iridium or platinum, which is more durable material than was used in the past – and costly as a result.
That said, you should inspect your spark plugs every 30,000 miles or so to make sure they are still in good condition.
If you don’t maintain your spark plugs your engine will start to run rough, and several troublesome issues could develop over time, such as trouble starting your car, misfiring (which can damage your catalytic converter) and poor fuel consumption.