Bad Spark Plug Symptoms: How To Tell if Your Plugs Are Bad

You could have all the premium fuel in your gas tank, the most technologically advanced combustion engine under the hood, and some of the most cutting-edge technology you could ever want in your car.

But if your spark plugs are bad, it’s going to wreak havoc with your driving experience.

Who thought something as small and cheap would play such an important in the proper functioning of your engine.

Spark plugs are literally the reason why the air-fuel mixture in your engine cylinders gets ignited, kickstarting a series of events that make your wheels turn.

Needless to say, they need to be checked regularly and replaced when the need arises. That’s why many car manufacturers go out of their way to make it as easy as possible to replace them.

But how do you know when it’s time to do so?

In this guide, we’ll tell you all there is to know about the telltale signs of bad spark plugs so that you know exactly when to replace them.

Symptoms of Bad Spark Plugs

Worn out spark plug

Most problems in your car can be diagnosed simply by keeping your eyes, ears, and nose open. Sure, you can always just go to the mechanic, but being able to tell when something is up with your vehicle will go a long way.

Being more aware of your car’s needs will make you proactive, and push you to carry the right tools and spares in the car at all times, should the need arise when you least expect it.

Here are the top symptoms of bad spark plugs.

Car Hesitates to Start

Person starting a car

This could be an indicator of many different issues with your car, let alone bad spark plugs. But if this happens, it’s worth investigating your spark plugs first.

Worn-out spark plugs cause your engine to work harder because of the mismatch between spark timing and piston position. This could lead to a long cranking time before your car starts. If your car doesn’t start at all, the battery could likely be the culprit.

Poor Fuel Economy

Empty fuel tank warning light

Bad spark plugs can easily damage your ignition coil which can snowball into a variety of problems like inefficient burning of fuel and misfiring. The latter can cause the engine to send raw fuel into the exhaust stream which might also damage your catalytic converter.

Together, these issues lead to poor fuel economy and you might find yourself having to visit the gas station more frequently.

Inconsistent Idling

Tachometer showing inconsistent idling

As mentioned above, when the engine misfires, it sends unburned fuel into the exhaust system which sends mixed signals to the O2 sensor.

The O2 sensor will register that as your engine running too rich which will cause your ECU to incorrectly regulate your fuel mixture, making it run too lean. This causes rough idling and might make the misfiring issue even worse.

Choppy Acceleration

Foot on gas pedal

Another problem caused due to your engine running lean and misfiring is poor and choppy acceleration. You might notice that your engine pace loses momentum and then catches back up intermittently.

This is a classic case of bad spark plugs and fixing it is neither difficult nor expensive. Average spark plug replacement costs are extremely low. So if you are starting to notice the symptoms of bad spark plugs, you know exactly what to do.

Concluding Summary

If you’ve never performed any DIY maintenance on your car but wish to do so, replacing your spark plugs is a great place to start. In general, most spark plugs last around 20,000 miles, but you’ll probably want to replace them much more often than that.

The more vigilant you are of any abnormalities in your car, and the more mechanically proficient you become, even harder maintenance jobs will get easier.

What spark plugs do you use? Let us know by leaving a comment below!

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