How to Check Spark Plugs: Easiest Way to Check Your Plug

Most spark plugs wires are just as important as the spark plugs themselves, and a damaged or worn-out wire can lead to poor engine performance, misfires, and even engine damage. To avoid these issues, you should regularly inspect and check your spark plug wires. In this blog post, we’ll cover some essential tips and tricks for checking the condition of your car’s spark plugs and determining when they need to be replaced.

Signs of Worn-Out Spark Plugs

As with any mechanical component, spark plugs will eventually wear out and need replacing. It’s essential to be able to recognize the signs of worn-out spark plugs so that you can avoid more severe engine problems down the line. Here are some signs that your spark plugs might be worn out:

  • Poor Mileage: If your car’s mileage has worsened, it’s a sign that the spark plugs are no longer functioning correctly.
  • Rough Engine Idling: Spark plugs that are worn start to misfire, which causes a car to have a rough idle; once your car is idling, you may notice that the engine is a bit more shaky or jittery than normal.
  • Engine Start Problems: When your car has trouble starting, it’s often due to an issue with the spark plugs. 
  • Reduced Acceleration: If your car is experiencing reduced acceleration, it may be due to an issue with the spark plugs. 

How to Check Spark Plugs

How to check spark plugs

  1. Turn off the engine and wait for it to cool down. Remove the negative battery cable to prevent electric shock.
  2. Remove the spark plug tip by grasping the boot, which covers the plug and pulling it from the spark plug.
  3. Use a spark plug socket ratchet to loosen and remove the vehicle’s spark plugs from the cylinder head. You might need a wrench to remove tight plugs.
  4. Examine the spark plug for signs of wear, cracks or other damages. Buildups of carbon deposits, oil or other substances may also lead to plug failure.
  5. Check the gap between the centre and side electrode using a spark plug gap gauge or a feeler gauge. The gap should match the manufacturer’s recommended gap. If it’s too small or large, use a spark plug gapping tool to adjust the gap.
  6. Inspect the replacement spark plug for any signs of damage or dents before installing it. You may also need to coat the threads on the spark plug with anti-seize to help ease future removal.
  7. Use a torque wrench to tighten the spark plug to the recommended level spec in the owner’s manual. Remember not to over-tighten, as it might damage the threads or break the spark plug.
  8. Replace the spark plug wire by pushing the boot back over it until it’s seated. Repeat the process for other spark plugs.

How to Check Spark Plugs Without Removing Them

Step 1: Crank the Ignition

The first thing you need to do is get your engine running so. You can check the spark plugs while they’re in use.

To do this, turn your key in the ignition until you “crank” the engine until you hear the engine start-up. Make sure your vehicle is parked in a safe area, away from busy roads or pedestrians.

Step 2: Listen Carefully

Once your engine is running, listen carefully to the sounds it’s making. You’re looking for unusual noises that could indicate a problem with your spark plugs. For example, if you hear a knocking or pinging sound, this could mean that one or more of your spark plugs is not firing properly.

Step 3: Look for Vibrations

As you listen to your engine, pay attention to any vibrations you feel in the vehicle. If your spark plugs aren’t working correctly, your engine could be misfiring, causing vibrations throughout the vehicle. If you feel any shaking or hopping, this could be a sign of spark plug problems.

Step 4: Check for Smoke

Another symptom of faulty spark plugs is smoke coming from the exhaust pipe. If you notice smoke or excessive exhaust from your vehicle while running, this could signify a misfiring spark plug.

Pay close attention to the colour and smell of the smoke – if it’s dark or has a foul odour, this could be a sign of a more severe problem.

Step 5: Inspect the Spark Plug Wires

While your engine is running, closely examine the wires connected to your spark plugs. Ensure they’re firmly connected and the wire has no cracks or breaks. Damaged wires can lead to weakened signal transmission, reducing the efficacy of the spark plug.

Step 6: Take Note of the Dashboard

Many modern vehicles will have an engine light or other dashboard indicator if something is wrong with the engine. If you notice any warning signs, such as the engine light coming on or flashing, this could indicate a problem with your spark plugs.

How to Check Spark Plugs With a Multimeter

Step 1: Ensure the Engine is Cool

Before starting any work on your engine, it’s important to ensure it’s cool to the touch. Working on a hot engine can result in injury or damage to the engine.

Step 2: Disconnect the Spark Plug Wires

Locate the spark plug wires and gently disconnect them from the spark plugs. You may have to use a pair of pliers to grip the rubber boot of the wire and gently twist and gently pull it away from the spark plug.

Step 3: Remove the Spark Plugs

Using a spark plug socket, remove spark plug from the engine. If you need help determining which spark plug needs to be checked, consult your vehicle’s owner’s manual or a professional mechanic.

Step 4: Set the Multimeter

Turn the multimeter to the ohms setting and set the dial to the lowest resistance range. Alternatively, if your multimeter has an auto-range feature, you can also use that.

Step 5: Connect the Multimeter

Attach the multimeter’s leads to the spark plug tester terminal. The positive lead should be connected to the central terminal, while the negative lead should be connected to the metal shell surrounding the ceramic insulator.

Step 6: Check the Resistance

Once the leads are connected, check the multimeter reading. A healthy spark plug should have a resistance between 5,000 and 15,000 ohms. If the resistance reading is outside this range, the spark plug may be faulty and need replacing.

Step 7: Repeat for Each Spark Plug

Repeat steps 3 through 6 for each spark plug in the engine to ensure they all function properly.

How to Test Spark Plugs On Outboard Motor

Step 1: Locate the Spark Plugs

The first step in checking your spark plugs is to locate them. On most outboard motors, the spark plugs will be located on the top or side of the engine block. Consult your owner’s manual if you need clarification on the location.

Step 2: Remove the Spark Plugs

With the location of the spark plugs identified, the next step is to remove them. You can use a spark plug wrench to do this. Turn the wrench counter-clockwise to loose spark plug before removing it completely.

Step 3: Inspect the Spark Plugs

Once you’ve removed the spark plugs, it’s time to inspect them. Here are some things to look for:

  1. The colour of the spark plug: A healthy spark plug should be light brownish-grey. If it’s too white, it means that the engine is running too lean; if it’s too black, it means that the engine is running too rich.
  2. The electrodes on the spark plug should have a smooth and clean appearance. If they’re too worn or corroded, you should replace them.
  3. The gap between the centre electrode and the ground electrode: The gap should be within the manufacturer’s specifications. If it’s too large or too small, it can cause problems with the ignition system.

Step 4: Clean or Replace the Spark Plugs

After inspecting the spark plugs, you should determine whether they can be cleaned or need replacing. You can clean them using a wire brush or a specialized spark plug cleaner if they’re just dirty. However, you should replace them if they’re rusted or worn out.

Step 5: Install the Spark Plugs

Once you’ve cleaned or replaced the spark plugs, it’s time to install them back into the engine block. Tighten them using a spark plug wrench, ensuring they’re snug but not overly tight.

How to Check Spark Plugs On Lawn Mower

How to Check Spark Plugs

Step 1: Turn off the Lawn Mower

First, make sure your lawn mower has cooled down before attempting anything. You don’t want to burn yourself or risk damaging the spark plug.

Step 2: Access the Spark Plug

Remove the engine cover by unscrewing the bolts and holding it in place so the spark plug is visible.

Step 3: Remove the Spark Plug

Use your spark plug socket to remove the spark plug from the engine. Twist it left to unscrew it from its housing. Be careful not to drop it into the mower’s engine compartment.

Step 4: Check the Spark Plug

Inspect the Spark Plug for signs of wear, fouling, or damage. If it looks clean, with no electrode deposits, it’s in great condition. If the electrode looks burnt, corroded, or covered in deposits, then it’s likely the problem.

Step 5: Check the Spark Plug Gap

Refer to the manufacturer’s manual for the recommended gap measurement. Check the gap between the two electrodes using a spark plug gap gauge. If it doesn’t match the manual’s recommended gap, adjust the gap as needed.

Step 6: Reinstall Spark Plug

If your spark plug is still in great shape, screw it back into its position on the engine. Make sure it’s secure but not over-tightened.vo


Spark Plugs Recommendation


  • How often to Check Spark Plugs

Experts recommend that you should check your spark plugs every 30,000 miles or as recommended by your vehicle manufacturer. Regular inspection and replacement of your spark plugs can help prevent engine misfires, decrease your emissions, and improve air fuel mixture efficiency.

  • How Much Does It Cost To Check Spark Plugs

If you take your car to a mechanic for a spark plug check, you can expect to pay anywhere from $40 to $350 or more. This cost will typically include labor and parts, but the price can vary depending on the complexity of the job and the hourly rate charged by the mechanic.

  • How Hard Is It to Check Spark Plugs

Checking spark plugs is a relatively simple process that you can do on your own, provided you have the necessary tools and knowledge to do it.

  • How many km do spark plugs last?

There are different types of spark plugs, including iridium, platinum, and copper. Iridium spark plugs are known to be the most durable, lasting up to 100,000 kilometers. Platinum spark plugs, on the other hand, are designed to last around 60,000 kilometers to 80,000 kilometers. Copper spark plugs are the cheapest but need to be changed more frequently, around 20,000 kilometers to 30,000 kilometers.

  • How long do NGK spark plugs last?

NGK spark plugs typically last between 40,000 and 50,000 miles before it needs to be replaced. However, the lifespan of the spark plug can vary depending on several factors such as the type of vehicle it’s installed in, driving conditions, and driving habits. In general, NGK spark plugs are durable, reliable and designed to last.

  • What is the life of a spark plug?

Generally, spark plugs are designed to last between 30,000 to 100,000 miles, depending on the type of spark plug, the driving conditions, and vehicle manufacturer’s recommendations. However, an average lifespan for a spark plug is around 80,000 miles.


In conclusion, taking good care of spark plugs is essential for the smooth functioning of any vehicle. Regular inspection, cleaning, and replacement can save you from potential engine problems and also increase fuel efficiency.
By following the steps outlined in this guide, you now know how to check spark plugs. Remember, if you are unsure about any aspect of spark plug maintenance, it is always best to seek the help of a professional mechanic to replace new plug.

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