Spark Plug Symptoms: Signs Your Engine Is Struggling

When your car sputters, stalls, or refuses to start, the culprit might be something small but critical: the spark plug, a small component that ignites the fuel-air mixture in your engine’s cylinders. Also known as ignition plug, it’s not something you think about until your engine starts acting up. Even though spark plugs last 30,000 to 100,000 miles depending on type, they don’t last forever—and when they fail, your engine knows it.

One of the clearest signs is a rough idle, when the engine shakes or vibrates while stopped at a light. That’s not normal wear—it’s a misfire. A failing spark plug can’t ignite fuel cleanly, so one or more cylinders skip their turn. You’ll also notice poor fuel economy, because unburned fuel gets pushed out instead of powering your car. If you’re filling up more often than usual, it’s not just gas prices—it’s your spark plugs. Then there’s the engine misfire, a sudden loss of power when accelerating. It feels like your car hesitates or stumbles, especially going uphill or merging onto the highway. And if you hear a clicking or popping sound from the engine, that’s another red flag.

Some drivers ignore these signs, thinking it’s just an old car acting up. But bad spark plugs don’t just make driving annoying—they can damage your catalytic converter, hurt your emissions, and eventually leave you stranded. The good news? You don’t need a mechanic to spot these symptoms. You can feel them, hear them, and even see them in your dashboard warning light. And once you know what to look for, replacing them is often a simple fix.

Below, you’ll find real-world guides that break down what these symptoms mean, how to test your plugs yourself, and when it’s time to swap them out. No guesswork. No fluff. Just what actually works.