Spark Plug Inspection: How to Check, Diagnose, and Fix Common Issues

When your car sputters, misfires, or won’t start, the problem often starts at the spark plug, a small but critical component that ignites the fuel-air mixture in your engine’s cylinders. Also known as ignition plug, it’s one of the few parts you can visually inspect without tools—and the first place to look when performance drops. Most drivers ignore spark plugs until the engine light flashes, but a quick inspection every 15,000 miles can prevent bigger repairs and save you hundreds.

Spark plugs don’t just fire—they tell you what’s happening inside your engine. A black, sooty plug means your fuel mixture is too rich. A white, burnt tip signals overheating or wrong heat range. Oil residue? That’s a sign of worn valve seals or piston rings. Even the gap between the electrodes matters: too wide, and the spark weakens; too narrow, and it can’t ignite properly. These aren’t guesses—they’re facts mechanics use every day. The ignition system, the network of wires, coils, and modules that deliver high-voltage electricity to the spark plugs depends entirely on healthy plugs. A single faulty plug can throw off fuel economy, reduce power, and even damage your catalytic converter over time.

And it’s not just about age. Driving habits matter. Short trips with frequent cold starts? That’s carbon buildup waiting to happen. Constant highway driving? Plugs last longer but still wear out. You don’t need a diagnostic tool to see the truth—just a socket wrench, a flashlight, and five minutes. Many of the posts below show real-world examples: how a dirty plug caused a misfire in a Honda Civic, why a Toyota Camry lost power after 60,000 miles, and how a simple inspection caught a failing coil before it killed the whole ignition system.

There’s no magic to spark plug inspection. It’s not about buying the most expensive plug or following a rigid schedule. It’s about reading the signs. The posts you’ll find here cover everything from basic visual checks to advanced diagnostics—like how to test for spark without removing the plug, what to look for when comparing old and new plugs, and which brands actually hold up under real driving conditions. Whether you’re a weekend mechanic or just trying to avoid a tow truck, this collection gives you the facts you need to act before your car leaves you stranded.