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Spark plugs emit that crucial flicker of electricity that is needed to ignite the mixture of fuel and air that brings your engine to life and powers your vehicle to move forward. They are a small but crucial and powerful component in the complex structure of your engine. What’s more, they last for a long time, as long as 90,000 miles in some cases. Even at their more frequent change rate, you won’t need new spark plugs for some 30,000 miles.

Mighty and durable as they are, they do eventually start to fail. Since your car can’t do even one moment with faulty spark plugs, it pays to know the signs that your spark plugs are near failure. Armed with this knowledge, you can get them replaced in time.

Sign 1: Engine Misfiring

Your engine misfiring can quickly turn into a very serious issue for your vehicle. If you’ve ever seen your “Check Engine” light come on and it’s flashing, that means your car has experienced serious misfiring and needs immediate attention from a mechanic. If the misfiring is caused by faulty spark plugs, it may not be quite as serious, but it does mean that your spark plugs are near the end of their lifespan.

If you’re wondering what a misfire would feel like as you’re driving, it would seem as though your car were somehow hesitating or juddering before “finding its groove” again.

Sign 2: Suffering Fuel Economy

Another very noticeable sign of faulty or failing spark plugs is a diminishing fuel economy. Have you noticed that you’ve been filling up at the petrol pump more frequently than usual? Is your monthly fuel budget not stretching far enough? A number of things can cause that increase in fuel consumption, and one of them is a dirty, damaged or failing spark plug.

How is your spark plug connected to your miles-per-gallon rating? As we mentioned further above, spark plugs ignite the air-fuel mixture that comes into your cylinders. That ignition is what gives your engine power. Your car typically has one spark plug per cylinder. Therefore, if one fails, that’s one cylinder not providing the combustion you need, which then leads to sluggish acceleration (see below). Your engine has to work harder to compensate, thus more fuel gets used up.

Sign 3: Sluggish Acceleration

If you find your foot pressing the accelerator increasingly lower to the ground without much effect, then you might have faulty spark plugs on your hands. As we explained above, the spark plugs ignite the fuel-air mixture in each of your cylinders. Let’s say your car has 4 cylinders — as many do — then losing even one spark plug is losing 25 percent of your fuel combustion strength.

That has a marked effect on your acceleration. Try to keep a sense of how far down you’re depressing the pedal when you accelerate. The deeper you’re going, the more likely it is that the acceleration is being affected by something, and possibly bad spark plugs.

Sign 4: Difficulty Starting the Car

When you’re struggling to start the car in the morning, faulty spark plugs aren’t necessarily the first thing that comes to mind. As you reach the third or fourth attempt to start the vehicle, you’re probably beginning to think about the battery, or whether you have enough petrol in the tank. Perhaps at the fifth or so attempt, the engine fires up, you see you have petrol, and so you dismiss the incident as unimportant.

What you might have just witnessed is your spark plugs struggling to provide that flicker of ignition in the cylinders that gets the engine going.

Sign 5: Rough Idling

When you pull your car up to the traffic lights, up to a T-junction or to a “Stop” sign, what do you hear? Is the engine humming along as normal, or do you sense any kind of juddering or vibration? Even drivers with limited mechanical knowledge can tell when something doesn’t sound right in the engine. A louder-than-usual idling sound, vibrations or other rattling or knocking sounds are never a good sign.

These vibrations can mean many things, so don’t automatically assume that it means you definitely need new spark plugs. If it so happens that you haven’t changed them in a long time (25,000 miles or more) then faulty spark plugs could be the issue.

Sign 6: The “Check Engine” Light is On

Finally, this is a problem we touched on further above, but it warrants its own entry. If you see the “Check Engine” light, then spark plugs being near the end of their life is a possible cause. If the light comes on and is flashing, then it means a serious misfire has happened and your car needs immediate attention.

If the light is steady, it could just be giving you advance warning of the need to change your spark plugs. In any event, respond promptly to the “Check Engine” light.

Conclusion: Faulty Spark Plugs are a Red Line – Change Them Promptly

As we mentioned above, your car simply cannot function properly without working spark plugs. If you notice any of the above signs, or have other reason to believe that your car’s spark plugs are having problems, then pay a visit to your mechanic at the earliest opportunity. If you end up stranded or stuck at home, you’ll face the additional cost of either a mobile mechanic or a tow truck to bring your car to the garage.

Finally, you could also consider asking your mechanic about longer-lasting or otherwise higher-quality spark plugs. They’ll cost a little more, but they’ll pay for themselves in longer life and help deliver you greater peace of mind. Look out for the signs and stay safe on the road.