How To Replace Your Vehicle’s Spark Plugs

replace spark plugs

Each cylinder in your car’s engine is equipped with at least one spark plug (some vehicles have two per cylinder). One end is connected to the ignition coil. The coil transmits voltage, which is used by the spark plug to ignite the air-fuel mixture in the combustion chamber. This occurs seamlessly over tens of thousands of miles.

A spark plug will eventually need to be replaced in order to maintain your engine’s performance. While most people rely on their mechanics to do the job, you can easily do it on your own. We’ll describe the process in this article. First, we’ll explain some of the reasons spark plugs need to be replaced periodically.

Reasons To Change Your Spark Plugs

When plugs are new, they help your engine operate efficiently. There are few, if any, instances of misfire, and idling and stalling are rare. Over time, the electrode of the plug erodes, increasing the gap across which a spark must jump. This causes misfires to occur with greater frequency. As a result, your vehicle will experience increased emissions, hesitation during acceleration, and lower fuel economy.

Another problem with bad spark plugs affects those who live in cold weather. When the electrode becomes dirty or severely eroded, the spark is often unable to jump the gap to provide the necessary voltage for igniting the air-fuel mix. As a result, many drivers find it difficult to start their cars after leaving them idle for several hours. The colder it is outside, the worse this problem becomes.

Lastly, a dirty spark plug that causes a misfire will produce excessively high emissions. Unburned fuel will move into the exhaust system. Your car’s catalytic converter, normally tasked with cleaning exhaust gases of harmful byproducts, is ill-equipped to handle the fuel. In many cases, the component overheats.

So, how often do you need to replace your spark plugs? This depends, in part, on the brand you purchase. The normal service interval is 30,000 to 40,000 miles. However, if your engine is running rich (i.e. too much fuel), or other problems have developed, your plugs may become fouled sooner. Thus, even the premium plugs that boast a service interval of 100,000 miles should be inspected at 40,000 miles.

Locating And Removing The Plug Wires

Replacing spark plugs is simple as long as you follow the method described here. You’ll need a few tools, including a ratchet wrench, and spark plug socket and extension.

Lift the hood of your car, and locate the top of the engine. You’ll notice several rubber tubes; these are plug wires. A spark plug is connected to the end of each wire. You’ll be tempted to remove all of the plug wires at once. Instead, remove one at a time, replacing the spark plug on the end before removing the others.

The reason for doing this is because your engine’s cylinders fire in a predefined sequence. If you replace the spark plugs out of order, you’ll affect the operation of your engine.

Removing And Inspecting The Spark Plugs

After you remove the first plug wire, use your socket and extension to remove the spark plug from the cylinder. You’ll need to use the wrench to unthread the plug. Take care not to inadvertently strip the thread.

With the spark plug removed, inspect its electrode. The deposits you observe will provide important clues regarding your engine. For example, black material on the end suggests the cylinder is running rich, or oil is somehow getting into the combustion chamber. Both problems should be addressed prior to installing the replacement plug.

Also, if the electrode appears damaged in any way, there’s a good chance the plug is the wrong type for your engine.

Install The New Plugs And Crank The Engine

The last step is to screw in the replacement spark plug. Use the socket to gently guide it into its compartment. Then, begin turning it clockwise by hand to tighten it. If you encounter resistance, avoid forcing the plug since doing so can damage the compartment’s threads. Once the spark plug has been screwed in (by hand) as far as it will go, use the ratchet wrench to tighten it further. Make the fit snug, but resist tightening it too far.

After all of the replacement plugs have been installed, start your car and listen to the sound of the engine. It should be smooth, and without misfires or a rough idle.


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