Spark Plug Basics: Signs, Replacement & Performance Tips

When working with Spark Plug, the tiny metal device that creates the spark to ignite the air‑fuel mix in each cylinder. Also known as ignition plug, it sits at the heart of the Ignition System, the collection of coil, wiring and control modules that deliver high‑voltage electricity to the plug and directly shapes Engine Performance, how smoothly the engine runs, how much power it produces and how quickly it responds. A fouled or worn plug can cause misfires, drag down Fuel Economy, the miles you get per litre of fuel and even overheat the Catalytic Converter, the emissions component that strips harmful gases from the exhaust. Knowing these links helps you catch problems before they leave you stranded on the roadside.

How to Spot Bad Spark Plugs and When to Replace Them

Most drivers notice a rough idle, a jumpy acceleration or a sudden drop in MPG before the plug actually fails. Those symptoms are the engine’s way of saying the spark isn’t strong enough or timing is off. Look for a yellow‑brown glaze on the tip, cracked insulators or a gap that’s wider than the manufacturer’s spec. If you hear a consistent ticking at idle, that’s often a sign the plug is firing late or not at all. In the UK, a typical copper‑core plug lasts about 20‑30 000 miles, while iridium or platinum versions can stretch to 60‑100 000 miles, but the real clock starts ticking as soon as you notice any of the warning signs.

Replacing a spark plug is one of the easiest DIY tasks you can do, and it pays off quickly. First, check the service manual for the correct gap – most modern engines use a gap between 0.6 mm and 1.2 mm. Use a feeler gauge to set the gap on the new plug before you install it. Tighten the plug by hand until it’s snug, then give it a final ¼ turn with a torque wrench (usually around 20 Nm). Re‑connect any ignition coils or wires, start the engine and listen for a smooth, steady idle. If the engine still misfires, you may have an upstream issue like a weak coil or a clogged fuel injector, but a fresh plug often solves the problem.

Below you’ll find a curated collection of articles that break down the whole process – from spotting early symptoms, through step‑by‑step replacement instructions, to cost estimates and tips for extending plug life. Whether you’re a DIY enthusiast or prefer to hand the job to a professional, the guides will give you the confidence to keep your engine firing on all cylinders.