Spark plugs

How Do I Know If My Spark Plugs Are Bad?

Daniel McDonald
Daniel McDonald5 min read
How Do I Know If My Spark Plugs Are Bad?

Are you dealing with faulty spark plugs? Does your car have worn-out spark plugs or any similar spark plug problem? This article will answer all your questions and concerns.

What Is A Spark Plug?

Spark plugs are a device responsible for igniting the air-fuel mixture in cars. They are metal threaded shells with electrical isolation from a central electrode through a ceramic insulator. Spark plugs supply the spark that creates the explosion, and trigger combustion, so your engine can produce power.

Although small, they are mighty and have a crucial role in your car's performance. Their function is to screw into the internal combustion of the cylinder head and ignite a spark that will light up the mixture of air and fuel. Their part is to screw into the internal combustion of the cylinder head and ignite a spark that will light up the mixture of air and fuel.

How Do You Know You Have A Faulty Spark Plug?

Like motor oil, air filters, fuel filters, etc., spark plugs need regular maintenance and service. In most cases, people replace spark plugs between 30,000 to 50,000 miles. In addition, spark plugs need to burn fuel efficiently, or they might not be able to start the engine.

Below you can find out the most common signs of spark plug failure.

1. Fuel Economy Rate

So, you are filling up the gas tank much more than you used to? This sign could mean failing spark plugs. An unexpected drop in fuel economy and reduced gas mileage could mean worn spark plugs.

If a spark plug does not function properly, the gap between the electrodes in the plug might be too close or too far, leading to an incomplete combustion process. So, the sparks can fire or not fire. First, a mechanic would examine the plug to see if the gaps need adjustment. Then, they will adjust it according to the owner's manual. Only then will they decide if you need the spark plugs replaced.

Deteriorated spark plugs can significantly increase fuel usage since they will not effectively burn the fuel that goes to the engine. Consequently, you will be disappointed with the gas mileage, constantly visiting the gas station.

So, if the spark plugs are not working correctly, you might consider replacing them.

2. Engine Misfires

If your engine misfires, you should be worried. A misfire means that some of your spark plugs are not functioning correctly, and there is a problem with the ignition system. Usually, if the engine misfires, you will hear sputtering sounds and violent shaking since something interrupts the combustion process. The reason might be a spark plug wire, or the cylinders are not firing correctly. Also, it could be the spark plug tip that connects with the wire, which might be damaged.

So, you must have the spark plugs checked regularly. If you let the engine misfire repeatedly, you will see more exhaust emissions, which will lead to a decrease in engine power and an increase in fuel consumption.

3. Trouble Starting

If you have trouble starting your vehicle's engine, you might first blame the battery. First, however, consider replacing the old spark plugs with new ones. Damaged or failing spark plugs cannot deliver the spark necessary to start the engine. Also, you need to check the gap on the spark plug. Most often, this is an issue in winter and cold weather.

New spark plugs will easily create the spark, generating power for the vehicle. With older plugs, the car might crank for a long time before it starts.

Although the reason for hard starting most often is an empty gas tank or a dead battery, sometimes the only culprit could be the spark plugs.

4. Slow Vehicle Acceleration

Most often, slow acceleration happens due to some issue in the ignition system. And sometimes, your car will not respond when you press the gas pedal because of a bad spark plug. The trouble with spark plugs in your vehicle might result in delayed response and poor acceleration.

When the materials of the spark plug wear out, the spark plug is less effective and can reduce the acceleration ability of a car. Of course, if you are facing this problem, contact your mechanic first since poor acceleration can happen due to other factors such as bad fuel filters or clogged fuel injectors.

5. Rough Idle

Rough idling is one of the most frequent signs of bad spark plugs. If you notice that your engine makes some odd sounds and vibrations resulting in rough idling, check the spark plugs. Knocking, rattling, and noisy idling from the engine can all happen due to dirty/faulty spark plugs. A cylinder might misfire only when idle.

A bad spark plug can make your vehicle's engine sound rough when idling. So, contact your mechanic sooner to avoid any further costly repairs.

6. The Check Engine Light Goes On

If you see the check engine light in the dashboard, a worn-out spark plug might be the culprit. Since the bad plugs can cause a misfire, the engine light will pop on immediately.

So, as part of your car maintenance, you must regularly check or replace the plugs. This way, you will avoid any repairs. In addition, you can damage the exhaust cleaner (the catalytic converter) if you drive the car with dirty plugs.

Of course, the check engine light in your car can turn on due to several things. First, to ensure the vehicle needs repair, you can call our technicians to check the car's performance.

7. Oil Contamination

You need new spark plugs for your car if there is a fuel or oil contamination. First, remove the old plugs and compare them to the new ones. If you find any contamination, replace the plugs to improve vehicle performance.

However, you need closer inspection to determine if the contamination happens due to oil, fuel, or the coolant.

How Often Should You Replace Car Plugs?

Of course, if you notice your car has dirty or bad spark plugs, you need to replace them immediately. However, regular plug maintenance should happen every 80,000 to 100,000 miles since car plugs have a long lifespan and are highly durable.

However, the sparks are already old once you reach 80,000 miles with your car. Therefore, they will lead to weaker engine performance. So, you might consider spark plug maintenance every 30,000 to 40,000 miles.


What Is The Sound Of A Bad Spark Plug?

Bad spark plugs will cause a knocking sound when you accelerate. So engine knocking happens if the spark plugs are not igniting all the fuel. They will cause a rattling sound together with a vehicle vibration.

How Much Time Will Spark Plugs Replacement Take?

You can repair spark plugs in an hour if you know the basics. Also, you will save a lot of cash if you do it yourself. It is a simple task if you have any mechanical knowledge.

Will A New Plug Make The Car Run Better?

Most definitely. New plugs will improve the car's horsepower. Also, they will enhance the engine's overall performance, increase the gas mileage, and make the car run better. That is why regular maintenance is crucial.

What Can Make Spark Plugs Go Bad?

Spark plugs can wear out because of oil in the combustion chamber, repeated engine overheating, carbon buildup on the electrodes, or improper gap. Make sure you avoid these things to reach optimal engine performance.

Final Thoughts

Spark plugs are one of the most critical factors regarding proper engine performance. Whether your vehicle will take you places or fail depends highly on the spark plugs. Take care of their well-being and try not to drive the car if you suspect dirty/lousy spark plugs. Consult the mechanic and replace them regularly.