Car Runs Worse After Changing Spark Plugs: Quick Fixes and Tips

Changing your vehicle’s spark plugs can be essential to maintaining peak performance. However, sometimes after replacing them, you might notice your car running worse than before, leaving you puzzled and concerned.

This article will discuss why this happens and guide you on what to do when faced with this situation.

First, we’ll help you understand the importance of spark plugs and how they contribute to your car’s performance. We’ll then delve into the most common reasons for worsened performance after changing the spark plugs, such as incorrect gaps, using the wrong plugs, and wiring issues.

Moreover, we’ll emphasize the significance of selecting the right spark plugs for your vehicle, as well as proper installation and troubleshooting tips.

Lastly, we’ll touch on additional performance issues that could be related to components other than the spark plugs and provide answers to some frequently asked questions.

Car Runs Worse After Changing Spark Plugs - What to Do?

Understanding the Importance of Spark Plugs

Spark plugs play a crucial role in your car’s combustion process. They generate the spark needed to ignite the air-fuel mixture, ensuring smooth engine performance.

Choosing the right type of spark plug is critical. Check out some of the common types of spark plugs:

  • Iridium Spark Plug: Offers a longer lifespan and improved performance.
  • Conventional Spark Plug: Cost-effective but may not last as long as iridium.
  • Racing Spark Plug: Designed for high-performance engines but may not be suitable for everyday use.

Here’s a comparison table for these three types of spark plugs:

Type Lifespan Performance Price
Iridium Spark Plug Long High Higher
Conventional Spark Plug Medium Medium Lower
Racing Spark Plug Short Very High Highest

While iridium and racing spark plugs can improve engine performance and efficiency, they may be more expensive and not suitable for all vehicles.

Misfires can happen when there’s an issue with the spark plugs or another part of the ignition system. Significantly, a misfire can negatively impact engine performance. To avoid these problems, it’s important to:

  • Install the correct spark plug type.
  • Ensure proper gap size for optimal combustion.
  • Replace worn wire boots or faulty ignition components.

Common Reasons for Worsened Performance after Changing Spark Plugs

There are several possible reasons why your car runs worse after changing spark plugs. Here’s a brief overview of the most common causes:

  • Incorrect Gap: Spark plugs require a specific gap setting for optimal performance. If the gap is too wide or narrow, misfiring and rough idle may occur.
  • Wrong Spark Plug: Using the wrong type of spark plug for your car can lead to poor acceleration, stalling, and even expensive damage to pistons.
  • Damaged Spark Plug Wire: If the spark plug wire is damaged during installation, it can cause engine misfires and poor fuel economy.
  • Improper Gasket Seating: An improperly seated gasket can result in a leak, leading to a decline in performance.
  • Mixing Up or Reversing Spark Plug Wires: Installing spark plug wires in the wrong order or reversing them can cause poor acceleration and engine misfiring.

If you suspect any of these issues after installing new spark plugs, visiting a mechanic for proper diagnosis and repair is recommended.

Issue Symptoms Fix
Incorrect Gap Misfiring, rough idle Use a gap tool to adjust the gap properly
Wrong Spark Plug Poor acceleration, stalling, engine damage Install the correct spark plugs for your car
Damaged Spark Plug Wire Engine misfires, poor fuel economy Replace the damaged wire
Improper Gasket Seating Performance leak Reinstall the gasket correctly
Mixing/Reversing Wires Poor acceleration, engine misfiring Correct the wiring order

Remember, regular maintenance, and using the right parts will ensure optimal performance and prolong the life of your car.

Car Runs Worse After Changing Spark Plugs - What to Do?

Choosing the Right Spark Plugs

Choosing the correct spark plugs for your car is essential to ensure optimal performance. Selecting the wrong type or size can cause your engine to run poorly or even result in serious damage.

  • Check your car’s owner’s manual for the recommended spark plug type
  • Cross-reference spark plug information with reliable sources

One popular spark plug option is the NGK 6619 Iridium IX Spark Plugs which provide durability and long-lasting performance.

They may be more expensive, but their quality makes them worth the investment. Additionally, you can consider Fomoco plugs as they are also known for their reliability.

Features NGK 6619 Iridium IX Spark Plugs Fomoco Plugs
Durability High High
Long-lasting Yes Yes
Price More expensive Moderate
Compatibility with cars Wide range Wide range

Keep in mind that using the correct type of spark plugs can:

  • Improve fuel efficiency
  • Provide smoother acceleration
  • Increase engine lifespan

Proper Installation and Troubleshooting

Proper installation of spark plugs is crucial for optimal engine performance. Ignoring the recommended settings may cause your car to run worse after changing spark plugs.

Here are a few essential steps and troubleshooting tips you should follow:

  • Check the spark plug gaps: Before installing new spark plugs, make sure they have the correct gap. Refer to your vehicle’s user manual for the appropriate measurements. An inappropriate gap can lead to engine issues.
  • Use the correct spark plugs: Always choose spark plugs that are compatible with your vehicle. Wrong spark plugs may cause damage to the ignition system and cylinder head.
  • Torque setting: Applying the appropriate torque is essential when installing spark plugs. Using a torque wrench helps ensure that spark plugs are tightened correctly, preventing damage to the cylinder head or ignition system components.
  • Firing order and spark plug wire placement: Mixing up spark plug wires can cause poor engine performance or even prevent the engine from running. Knowing your engine’s firing order and making sure wires are connected correctly is crucial.

If you have already installed your spark plugs and your car is running worse, consider these troubleshooting tips:

  • Double-check the gap size for each spark plug and make any necessary adjustments.
  • Ensure that you have used the correct plug types, and check if any plug is damaged or loose.
  • Inspect the torque applied to each plug, and verify if a torque wrench was used during the installation process.
  • Make sure that the spark plug wires are connected to the proper cylinder in the correct firing order.

Following these steps should ensure the proper installation and troubleshooting of spark plugs, leading to your car running smoothly and efficiently.

Car Runs Worse After Changing Spark Plugs - What to Do?

Addressing Additional Performance Issues

If your car runs worse after changing spark plugs, there are several factors that could be causing the issue. Besides the spark plugs, other components related to engine performance include fuel efficiency, ignition coils, oxygen sensors, and fuel injectors.

Here are a few possible causes resulting in performance decline, along with ways to troubleshoot and address them:

  • Dirty Air Filter: A clogged air filter can lead to rough idling and low fuel efficiency. Regularly inspect, clean, or replace your air filter.
  • Faulty Ignition Coils: Malfunctioning ignition coils can cause cylinder misfires, making the car sputter. Check your coils and replace them as necessary.
  • Leaking Vacuum Hoses: A vacuum leak could lead to rough idling and impaired emissions. Inspect and replace vacuum hoses as needed.
  • Injector and Fuel System Issues: Clogged or leaking fuel injectors can affect fuel efficiency and impair engine performance. So, you need to clean or replace the fuel injectors.

Factors affecting engine performance after changing spark plugs

Factors Pros Cons
Proper Gasket Seating Prevents leaks and boost engine performance Requires attention to detail when changing spark plugs
Quality Spark Plugs Prevents engine damage and ensures optimal performance May be more expensive than lower quality plugs

Here are some common features of high-quality spark plugs:

  • Designed for your specific vehicle make and model
  • Precise electrode gap measurements
  • Resistant to wear and corrosion
  • Ensure a consistent and clean spark

The Advantages of Upgrading to Performance-oriented Spark Plugs

For car enthusiasts looking to enhance their vehicle’s performance, upgrading to performance-oriented spark plugs can offer various benefits. High-performance spark plugs are designed to ignite the air-fuel mixture more effectively, resulting in better acceleration, smoother idling, and increased power output.

These plugs can be particularly advantageous for sports cars and modified engines, providing a noticeable improvement in overall performance.

The Role of Ignition Coils in Spark Plug Performance

Ignition coils are essential components in the ignition system that provide the high voltage needed to generate sparks in the spark plugs.

A malfunctioning ignition coil can lead to weak or inconsistent sparks, causing engine misfires and decreased performance. Regular inspection and maintenance of ignition coils are necessary to ensure that they are functioning correctly and supporting optimal spark plug performance.

Car Runs Worse After Changing Spark Plugs - What to Do?

Understanding the Impact of Electrode Material on Spark Plug Performance

The material used for the spark plug’s electrodes can significantly impact its performance and lifespan. For instance, iridium and platinum electrodes offer better resistance to wear and corrosion compared to conventional copper electrodes.

By choosing spark plugs with advanced electrode materials, car owners can experience longer-lasting performance and reduce the frequency of replacements, offsetting the initial higher cost.


Maintaining peak performance in your vehicle requires a comprehensive understanding of the critical role spark plugs play in the combustion process. By choosing the right spark plugs, ensuring proper installation, and addressing any post-installation issues promptly, you can keep your car running smoothly and efficiently.

Additionally, considering other components related to engine performance and fuel efficiency will help you troubleshoot any potential problems and maintain the optimal operation of your vehicle for years to come.

Frequently Asked Questions

Why is my car misfiring after spark plug replacement?

Car misfiring after spark plug replacement might be caused by incorrect gap or damaged spark plug wire.

Check the gap of the new spark plugs and make sure it’s within the recommended range for your vehicle. Also, inspect the wires for any visible damage.

Why does my car have slow acceleration after new spark plugs?

Slow acceleration after new spark plugs could be due to wrong spark plug type or mixing up spark plug wires. Verify that the correct spark plugs have been installed and ensure the wires are connected to the appropriate cylinders.

What causes loss of power after changing spark plugs?

Loss of power after changing spark plugs might result from inappropriate torque or improper gasket seating. Recheck the installation process, including torque specifications and gasket seating.

Should anything else be done after replacing spark plugs?

  • Inspect spark plug wires for damage or wear
  • Reset the ECU (if applicable)
  • Monitor fuel economy for any changes
  • Observe engine performance and check for any abnormal noises or vibrations

Why is there a rough idle post spark plug change?

A rough idle post spark plug change can be attributed to an incorrect gap or new spark plugs causing a rough idle. Double-check the gap and re-inspect the installation process.

What to do if the check engine light comes on after changing spark plugs?

If the check engine light comes on after changing spark plugs:

  1. Use an OBD scanner to read the error codes
  2. Address the specific issues causing the error codes
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Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

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