Spark Plugs: What They Are & How to Check Them

Spark Plugs: What They Are & How to Check Them

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Many components work in sync for your vehicle’s engine to run properly, and it’s a complicated process, to say the least. But here’s the short version:

The fuel pump draws gasoline through the fuel lines and into the fuel injectors.

The fuel injectors then spray it into the combustion chamber.

The air filter cleans incoming air for a pure intake charge.

And the spark plugs fire for the gasoline to ignite. 

There are also pistons, crankshafts, and more working in concert.

Though each component plays an important role, the spark plugs are especially significant, turning liquid gasoline into power.

What is a spark plug exactly? What do spark plugs do?

Let's look at these crucial parts of your vehicle’s combustion process, how to check them, and how to know when the time’s come to change your spark plugs.

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What is a spark plug?

Vehicles run on internal combustion engines. To produce horsepower, they have to combust a fuel source, which powers the pistons back and forth. 

When a fuel injector sprays gasoline into the combustion chamber, the fuel needs a mechanism to ignite and power the pistons. That's exactly where the spark plugs come in. 

A spark plug produces a brief spark that allows gasoline vapors to combust and push the piston downward. The spark plugs connect to the timing and electrical components known as the ignition system. A vehicle's ignition system ensures a spark that fires at the precise moment for ideal fuel combustion.

Several types of spark plugs are available: standard, platinum, and iridium. 

Standard copper spark plugs are an inexpensive option, well-suited to vehicles built before 1980 and in high compression or turbocharged engines. However, their basic metal composition — copper and nickel — tends to wear out quicker than other varieties. Additionally, standard spark plugs require more voltage to create a spark than platinum and iridium models. Standard spark plugs typically cost around $2-$3 each. 

Platinum spark plugs are akin to standard ones, but they add a platinum disc near the tip for increased longevity. Platinum spark plugs have an increased lifespan compared to standard versions, with the ability to drive 60,000 miles before needing to be replaced. They also generate the most heat of any spark plug, reducing carbon buildup in the process. 

For newer vehicles with coil-on-plug ignition systems, platinum plugs are recommended. However, platinum spark plugs are more expensive than standard options, costing $20-$25. 

Iridium spark plugs use the highly heat-resistant and durable metal iridium for enhanced durability and performance. Iridium spark plugs require the least amount of voltage and create a higher quality spark than other types. With their higher-grade materials, iridium spark plugs can last up to 100,000 miles before you change them. Iridium spark plugs tend to cost the most compared to standard or platinum options. 

Properly functioning spark plugs are essential to engine performance and your car's longevity. 

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Signs of bad spark plugs

Like many wear and tear items on a car, old spark plugs need replacement from time to time.

Several signs can indicate the need for replacing spark plugs:

  • If you have trouble starting your engine or it idles unevenly, that might indicate bad spark plugs. Also, if your car vibrates, that could lead to further mechanical issues. 
  • If the engine misfires or your vehicle lurches when you accelerate, it could be time for spark plug replacement. Not only is this condition uncomfortable, but it might lead to increased emissions.
  • If you notice increased fuel consumption, it could be worn-out spark plugs. Bad spark plugs decrease fuel economy, increasing your costs at the pump.
  • If you notice your engine running sluggishly, the plugs may no longer provide sufficient spark for optimum combustion.

How to check spark plugs

If your vehicle isn't running properly, you can visually inspect the spark plugs to diagnose the situation. It's essential to check every plug. While one might look fine, others could need replacement.

While removing the spark plugs with a socket, several signs indicate a bad plug.

If a spark plug's tip and side electrode are shiny, they might be fuel-fouled. That could result from rich fuel mixtures, plugs with an improper heat range, or ignition issues. The first thing to check is whether the plugs meet the heat range requirements of your particular vehicle. You can find this information in your owner's manual. Or, if you believe it's a fueling issue, you may need to schedule an appointment with a mechanic and have the fuel injection system inspected.

Carbon-fouled spark plugs have a blackened appearance along their tip and side. These dark spark plugs have many possible causes, including excessive fuel, leaking injectors, or prolonged driving at low speeds.

A spark plug with the side electrode burned away has undergone repeated pre-ignition and been running too hot. Pre-ignition is when the plug creates a spark too early, or there's not enough gasoline in the combustion chamber or the air/fuel mixture. In that scenario, it's good to inspect the fuel injection system and timing. 

When it's time for a new-to-you vehicle, you want something in great shape, from the spark plugs to the tires. And you'll probably want to sell or trade in your old one. But that can be a time-consuming hassle, and how can you know if you receive a reasonable price? But when selling your car to Shift, there's no need to worry about any of that. All you'll have to do is enter the make, model, year, and mileage on Shift's easy-to-use website, and you'll instantly receive a purchase offer that's valid for seven days. You can get a fair offer, better than at the dealership, driven by powerful machine learning algorithms and tons of data. With Shift, there is no need to spend the extra time waxing and washing the car. A little dirt will not affect the quote, and we fully detail the cars ourselves anyway before listing them for sale. With your old car sold, you can browse Shift's wide selection of fully inspected vehicles located across the country that you can purchase from the comfort of your own home.

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Author
Shift Editorial Team