6 Symptoms of Bad Spark Plugs – & Replacement Cost

When it comes to the overall performance of your vehicle, spark plugs play a crucial role. These small but mighty components ignite the air-fuel mixture in the combustion chamber, allowing your engine to run smoothly and efficiently. Like any other part of a car’s engine, spark plugs can wear out over time and cause various issues. We will explore 6 Symptoms of Bad Spark Plugs that indicate you may have bad spark plugs.

6 Symptoms of Bad Spark Plugs

Your car’s spark plugs may be small in size, but they play a crucial role in the smooth operation of your vehicle. These tiny components generate the power needed to move your car by ignoring the air-fuel mixture within the engine cylinders. Spark plugs can deteriorate over time and cause various issues that affect your car’s performance.

6 Symptoms of Bad Spark Plugs

One of the most noticeable signs of bad spark plugs is a rough and shaky driving experience. As the spark plugs fail to catch fire the fuel properly, each cylinder misfires or fails to fire at all. This results in a lumpy acceleration and an overall loss of power while driving.

1. Decreased Fuel Efficiency

These small but mighty components can wear out or become fouled, leading to various issues. One symptom of bad spark plugs is decreased fuel efficiency. When pins are worn or dirty, they fail to produce a strong enough spark. This causes your engine to work harder and burn more fuel than necessary, Decreasing mileage per gallon.

2. Engine Misfires

Providing the spark to burn up the fuel mixture inside your engine’s cylinders. When they start to fail, it can lead to various issues that affect your vehicle’s performance. We will explore 6 Symptoms of Bad Spark Plugs.

If you notice frequent engine misfires or rough idling, it’s likely due to faulty spark plugs. Misfires occur when the air-fuel mixture in one or more cylinders fails. This can result in an uneven running engine and cause it to shake or vibrate at idle. Another symptom is reduced acceleration and power loss.

3. Rough Idle

A faulty spark plug can lead to several problems, including an annoying and unsettling rough idle. A rough idle occurs when your car’s engine stumbles or vibrates while at rest, causing an uneasy feeling for both you and your passengers. Do you know the oil on a spark plug? If no then read Oil on Spark Plug – What It Means & What To Do.

When spark plugs become worn out or covered in deposits, they struggle to generate enough heat to burn the fuel mixture properly. Misfires occur in one or more cylinders during idling conditions, leading to an unpleasant shaking sensation.

4. Trouble Starting

Difficulty starting a vehicle with bad spark plugs is the lack of a strong electrical current that ignites the fuel-air mixture in the firing chamber. As spark plugs deteriorate over time, they can become worn out or covered in deposits, hindering their ability to produce a powerful spark. This result makes it harder for your car to start promptly.

5. Acceleration Problems

Are you experiencing issues with your vehicle’s acceleration? It could be a sign of bad spark plugs. When they wear out or become faulty, it can lead to various problems, including acceleration issues.

6 Symptoms of Bad Spark Plugs

You may notice that your car burns more fuel than usual for every mile driven. This decrease in fuel efficiency can hit your wallet hard over time if left unaddressed.

6. Knocking Sounds From the Engine

These knocking sounds are often described as a rhythmic clicking or tapping noise that becomes more prominent when accelerating. If you hear these noises, addressing them promptly is essential to prevent further damage.

When your spark plugs aren’t firing correctly, fuel may not burn entirely, leading to unburned fuel-air mixtures exploding irregularly during combustion.

How to tell If Your Spark Plugs Need to Be Replaced

Small components can wear out and lose their effectiveness. Knowing when to replace your spark plugs is crucial in maintaining optimal engine performance.

If you have to turn the key multiple times before the engine kindle or if it takes longer than usual for your car to start, it may indicate that your spark plugs are due for replacement. When spark plugs become worn or dirty, they struggle to create a strong enough spark resulting in decreased gas mileage.

How Often Should You Change Your Spark Plugs?

How often should you change your spark plugs? This is a common question among car owners, and the answer depends on several factors. It is recommended to replace spark plugs every 30,000 to 50,000 miles. This can vary depending on the type of vehicle you drive and the type of spark plugs installed.

The vehicle uses copper spark plugs; they may need replacement sooner than the standard interval mentioned above. Iridium or platinum spark plugs have a longer lifespan and can last up to 100,000 miles before needing replacement.

Several factors can lead to an earlier-than-anticipated failure of a spark plug: 

  • Such as oil seeping into the combustion chamber
  • Excessive heat
  • Accumulation of carbon
  • Incorrect spark gap

Cost to Replace Your Spark Plugs

The average cost to replace spark plugs can vary depending on several factors, including the type of vehicle you own and where you get the work done. You can expect to pay anywhere from $80 to $150 for a professional spark plug replacement at a mechanic’s shop. This estimate typically includes the cost of labor and the price of new spark plugs.

DIY enthusiasts can save money by purchasing spark plugs and following step-by-step instructions online or in repair manuals. The cost will be significantly lower, typically from $20 to $40 for four standard copper spark plugs.

Final Thoughts

Recognizing the 6 Symptoms of Bad Spark Plugs is crucial for maintaining the performance and efficiency of your vehicle. These indicators should not be ignored, from rough idling and misfiring to decreased fuel economy and difficulty starting. Regularly inspecting and replacing spark plugs can prevent more serious issues from developing, such as engine damage or reduced power output. By addressing these symptoms promptly, you can save both time and money in the long run. Don’t wait until it’s too late – take action to ensure your spark plugs are in top condition and keep your vehicle running smoothly.


Can bad spark plugs cause a car to shake?

Yes, when spark plugs start to fail, they can lead to engine misfires which may cause your car to shake or vibrate while driving.

How often should I replace my spark plugs?

It is generally recommended to replace spark plugs every 30,000 miles or per the manufacturer’s guidelines for optimal engine performance.

Can bad spark plug damage other engine components?

If left unattended for too long, faulty spark plugs can harm other components, such as ignition coils or oxygen sensors.

Rabia Riaz
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