How to Replace Spark Plugs: A DIY Guide

How to change spark plugs
Image source: Danil Chepko/123RF

Changing spark plugs is a significant milestone for car enthusiasts. It signifies an understanding of the importance of regular vehicle maintenance and the willingness to take on the task independently. If you’ve reached this point, congratulations! Rest assured, the process is not as intimidating as it may seem. Think of a spark plug as a large bolt that generates electricity. Ready to find out how it’s done? Keep reading for all the details.

Why Should You Replace Your Spark Plugs?

Car breakdown

The frequency at which you should change your spark plugs depends on the type of car you own and the current plugs in your engine. Generally, replacement intervals vary between 30,000 and 100,000 miles. To be certain, consult your owner’s manual.

Worn-out spark plugs can lead to a range of performance issues, including poor gas mileage, engine misfires, rough idling, and hesitation during acceleration. Eventually, your engine may refuse to start if the plugs are severely worn.

Step 1: Locate Your Spark Plugs

Spark plugs

Begin by verifying that your car is equipped with spark plugs. Nearly all vehicles have them, regardless of whether you own a Toyota Tercel or a Porsche 918 Spyder. However, if you drive a diesel-powered vehicle, it won’t have spark plugs. Diesel engines utilize compression-ignition, meaning the fuel-air mixture ignites without a spark. In this case, glow plugs are used instead.

Once you’ve confirmed the presence of spark plugs, you’ll need to locate them. In most modern cars, the plugs are found near the top of the engine, firmly secured into the cylinder head. Keep in mind that they might be concealed by wires or a plastic cover. Subaru owners should look to the side of the engine, as should owners of Porsche models with flat-four or flat-six engines.

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It’s important to identify the type of spark plugs your engine requires and how many are needed. Typically, the number of spark plugs is based on the number of cylinders in your vehicle. For example, a four-cylinder engine requires four spark plugs, while a V12 engine requires 12. However, some engines, like certain Mercedes V6s, use two spark plugs per cylinder. For precise information, consult your owner’s manual or reputable online sources.

When you look under the hood, you’ll likely see either a thick wire or a coil that supplies electricity to each spark plug. Modern cars often have individual coil packs per cylinder, while older cars feature a single coil for the entire engine. Unbolt the coil pack or carefully disconnect the wire to gain access to the spark plug.

Step 3: Remove the Old Spark Plugs

Before removing the spark plug, use a clean rag or compressed air to clear any debris from the surrounding area. Ensuring no foreign objects fall into the cylinder is crucial. Trust us, it’s a situation you want to avoid. Once the area is clean, use a socket to loosen the plug. It might require some effort, so a ratchet will make your job easier. Remember: “Righty tighty, lefty loosey.”

Before discarding the old plug, take a moment to inspect its electrode—the tip of the plug. This can provide valuable information about your engine’s condition, particularly if you’re working on an older vehicle. A black substance on the electrode indicates that your engine is running too rich, meaning there’s too much gasoline in the air-fuel mixture. A white substance suggests a lean condition, with too little gasoline in the mixture.

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Step 4: Set the Gap for the New Plugs

To install the new spark plug correctly, use a gauge to adjust the gap between the two electrodes. The gap specification can vary, typically ranging from 0.02 to 0.06 inches. For precise measurements, consult a dealer, your local auto parts store, or search online. Accuracy is essential during this step.

Step 5: Install the New Spark Plugs

Once you’ve set the gap, you’re ready to install the spark plug. Reassembly is the reverse of disassembly, but we recommend using a torque wrench to ensure the plug is properly tightened. It’s best to leave the “by feel” approach to the experts, as overly tight or loose plugs can cause costly damage.

Reconnect the coil or spark plug wire, reinstall any previously removed parts, and you’re done! Now, start your engine to confirm that everything is functioning as intended.

For more automotive articles and helpful tips, visit OnSpec Electronic, Inc..

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