How to & Guides

Common Signs of a Faulty Spark Plug

Spark plugs play a critical role in ensuring optimal combustion performance and safeguarding the electrodes from damage. However, spark plugs also require periodic replacement, as worn-out ones can significantly impact engine performance.

In this article, we will explore the symptoms of bad spark plugs and the process of replacing them.

Symptoms of a Faulty Spark Plug

Difficulty Starting the Engine

Difficulty turning over is a clear indication of bad spark plugs. A well-functioning spark plug ignites the cold fuel mixture, enabling smooth engine start-up. However, worn-out spark plugs fail to generate an adequate spark, making it challenging for the vehicle to start. It’s important to note that spark plugs undergo changes that affect their ignition capacity.

Hesitations During Acceleration

Another sign of bad spark plugs is hesitations during acceleration. Insufficient spark generation prevents the proper utilization of fuel injection, resulting in irregular ignition and subsequent hesitations. Startup acceleration can also be affected by faulty spark plugs.

Decreased Fuel Economy

Worn-out spark plugs contribute to increased fuel consumption. They can cause debris to accumulate in the combustion chamber, leading to a reduction in fuel economy by up to 30%. To mitigate this issue, it is crucial to promptly replace worn-out spark plugs. Additionally, worn-out spark plugs negatively impact gas mileage, leading to fuel wastage and incomplete fuel ignition.

Engine Misfires

The improper combustion caused by worn-out spark plugs can result in engine misfires. Insufficient spark generation prevents proper ignition, resulting in reduced force and incomplete combustion. Engine misfires manifest as carbon deposits on the spark plugs, intermittent engine sounds, performance issues, and other mechanical problems.

See also  Quick Guide: Understanding AC Capacitor Wiring Colors

Sluggish Performance

Sluggish performance is one of the most common signs of bad spark plugs. Reduced spark capacity affects engine performance, as worn-out spark plugs struggle to efficiently ignite the fuel mixture. As a result, the vehicle runs with lowered fuel injection, resulting in sluggish performance.

Lean Condition

Bad spark plugs can trick oxygen sensors, leading to a lean condition. Incomplete combustion and fuel dumping into the oxygen sensor can create this lean condition. A lean fuel mixture starting from the oxygen sensors can take time to provide essential information.

Check Engine Light

Insufficient combustion and persistent misfires can trigger the check engine light. Different issues may arise when the check engine light is on. To diagnose the problem, an OBD scanner or a multimeter can be used to read codes related to lean running and misfires. In this case, a visual inspection is recommended as the first step to identify the problem.

When to Replace Spark Plugs

Although spark plugs generally have good longevity, they do require replacement over time. Robustly constructed spark plugs can perform well without issues. However, the replacement interval varies depending on the type of spark plugs. It is generally advised to replace them every 10,000 to 15,000 miles. Platinum or iridium spark plugs can last up to 10,000 miles, while the average spark plug service life is around 30,000 miles.

Replacing spark plugs in sets is also important. Even if only one or a few spark plugs show excessive wear, it is recommended to replace the entire set. Professionals typically replace the entire set instead of just the worn-out ones to ensure optimal performance.

See also  Best Drone Deals: Score a Budget-Friendly UAV for $33 (and Save on DJI Mini)

How to Replace Spark Plugs

The process of replacing spark plugs may vary depending on the car model. Some models allow for easy replacement, while others require a bit more expertise. In V-engine models, accessing the spark plugs can be challenging, and novices may need to remove various engine parts. However, the general procedure for replacing spark plugs is the same for all car models.

Here are the steps to follow when replacing spark plugs:

  1. Remove the ignition coils and cables.
  2. Remove any parts obstructing access to the ignition cables and coils.
  3. Replace damaged spark plugs with quality ones of the appropriate length. Short spark plugs are recommended to prevent piston damage.
  4. Apply lubricant to the threads.
  5. Use torque to tighten the threads.
  6. Reassemble all the removed parts, including the ignition coils and cables.

How to Determine if a Spark Plug Needs Replacement

A visual inspection can help determine whether spark plugs require replacement due to wear and tear. Start by checking the terminal nut at the bottom and ensuring that it is free from dirt or rust. Wipe it with a dry cloth if necessary, as dirt and rust can affect the connection and damage the spark plug wires.

Inspect the ceramic insulator, which separates the center electrode from the ground electrode to control sparks at the tip. Cracks in the ceramic insulator can lead to misfires. Also, examine the ceramic tip for any chips.

Check for dirt and rust around the electrode. If present, sparks will not occur properly and may cause misfires. Clean any deposits of rust and dirt, but if they are too stubborn to remove, replacement is necessary.

See also  Flippy: Revolutionizing Fast Food with Robotics

Additionally, inspect the center electrode and the gap between the electrodes. The center electrode may wear out and become thin over time. If worn out, immediate replacement is recommended. Use a gap tool or a spark plug to check the distance between the old spark plug and the ground electrode. If the gap is significantly larger, it’s time to get a new spark plug.

Finally, look for corona stains on the spark plugs. Brown rusty stains on the ceramic’s edge can impact spark performance. Clean any rust accumulation around the oxygen sensor.


By replacing worn-out spark plugs at regular intervals, you can ensure optimal engine performance and maintenance. Recognizing the warning signs and acting promptly can prevent engine problems and save you money. Remember, well-maintained spark plugs contribute to better fuel efficiency.

To learn more about spark plugs and their importance, visit OnSpec Electronic, Inc.. Let us help you keep your engine running smoothly.

Related Posts

13 Possible Causes for Your AC Blowing Warm Air

The unbearable summer heat has arrived, and instead of cool relief, your air conditioning unit is blowing hot air. Despite your best efforts, you can’t seem to find…

How to Install a 3-Way Switch: A Comprehensive Guide

How to Install a 3-Way Switch: A Comprehensive Guide

If you need to control an electrical device from multiple locations, such as a staircase light, a 3-way switch wiring is essential. With this wiring setup, you can…

Are Beats Studio Buds Waterproof?

The advancements in technology have paved the way for the invention and development of various gadgets and accessories. One such popular and widely used gadget is wireless headphones,…

Quick Guide: Understanding AC Capacitor Wiring Colors

Capacitors are passive electronic components that store electrical energy in an electric field. They consist of two electrically conductive plates insulated with dielectric material. When voltage is applied,…

How to Add New Members to a Group Chat in iMessage?

Messaging applications like WhatsApp and Telegram have gained immense popularity in recent times. The reason for their widespread use is that, in addition to regular text messaging, they…

The Versatile Uses of an Angle Grinder

The Versatile Uses of an Angle Grinder

What is an Angle Grinder Angle Grinders are handheld devices that offer a multitude of functions, including cutting, deburring, polishing, and grinding. It is a highly adaptable tool…