How to Check Your Spark Plugs to See if One of Them is Bad

For all internal combustion engine car owners, spark plug wear is inevitable. Spark plugs typically last between 20,000 and 60,000 miles, depending on your driving style.

As a car owner, you will need to replace your spark plugs eventually. A spark plug replacement is a straightforward process that’s really affordable. So affordable that many mechanics recommend doing it at regular intervals as preventative maintenance. If you prefer to wait until you notice any symptoms of a bad spark plug, that’s fine, too. In fact, this article is for you. We’ll show you how to confirm that you have a bad spark plug.

Warning Signs That You Need a New Spark Plug

When one of your spark plugs goes bad, you’ll know. Your fuel economy and engine’s performance are drastically reduced. More specifically, you’ll notice some or all of these symptoms:

  • Rough, jittery idle
  • Trouble starting your engine
  • Misfiring engine
  • Engine hesitation and surging
  • Increased fuel consumption
  • Slow acceleration

Checking Your Spark Plugs in 8 Steps

Image Credit: DIY-time

The best way to determine if one of your spark plugs is bad is to physically inspect all of the spark plugs in your engine. This process takes only 30-60 minutes, depending on your level of expertise. You will only need a few basic tools, including a spark plug socket and ratchet.

To see if one of your spark plugs is bad, take the following steps:

  1. Open the hood.
  2. Disconnect the negative battery terminal.
  3. Remove the engine cover.
  4. Unplug the electrical connector from the ignition coil.
  5. Remove the ignition coil.
  6. Remove the spark plug.
  7. Inspect the spark plug to see if it’s bad (the next section will show you how to identify a bad spark plug).
  8. Repeat with the rest of the spark plugs in your engine.

What Does a Bad Spark Plug Look Like?

When examining your spark plugs, look out for the physical signs of a bad one:

  • Excessively eroded electrode
  • Cracked porcelain housing
  • Dry black sooty deposits
  • Wet black oily deposits
  • Greenish or whitish deposits

Be careful not to mistake a used spark plug in good condition for a bad one. A used spark plug has a light grayish-tan deposit, and it doesn’t have any cracks or erosion.

What if You Need to Replace a Spark Plug?

The first thing you need to do is to get a replacement spark plug. We recommend ordering genuine OEM spark plugs online if you want to save money. Dealerships will mark up the price by about 30%. It’s pretty easy to find the exact same OEM spark plug online for much cheaper. For example, we carry genuine OEM Nissan spark plugs at wholesale pricing. It doesn’t get any cheaper than that.

Once you have your replacement spark plug on hand, follow this easy step-by-step tutorial to replace your faulty spark plug.

Got any questions about checking your spark plugs? Contact us. We’ll be happy to help you out!