What is a Spark Plug and Why Does Your Car Need it?

Despite their small size, spark plugs are essential in the operation of your engine. More precisely, spark plugs provide the spark needed to ignite the air/fuel mixture in the engine.

What do Spark Plugs Look Like?

A spark plug is a small tube that's screwed into one of the engine cylinders. Each cylinder has one spark plug.

On the top end of the spark plug, there's a terminal. It’s connected to the ignition coil. On the other end of the spark plug, you'll find a ground electrode that’s made of high nickel steel. With the way the ground electrode is designed, it helps create a spark large enough to ignite the air/fuel mixture.

Also inside the spark plug is a resistor. It keeps the electrical current inside the plug from interfering with the rest of the vehicle’s electrical system. Not all spark plugs have this, though. Cheap aftermarket spark plugs usually come without a resistor. You’d always find a resistor in OEM spark plugs.

Another important component of a spark plug is the ceramic housing. It’s built to protect all of the components inside it from heat and other elements within the cylinder.

How do Spark Plugs Make Your Engine Run?

Your engine can't run without spark plugs. Spark plugs serve as the link between the ignition coils and the air/fuel mixture. (The ignition coils create the energy needed to make the spark) Your engine needs spark plugs to shoot artificial lightning bolts into the combustion chamber and light up the air/fuel mixture.

Here’s how the process works:

  1. You start your car.
  2. The battery powers up the ignition coils.
  3. The ignition coils transform the battery’s low voltage into a high voltage electric current.
  4. In a particular order, the ignition coils deliver the right amount of voltage to the spark plugs they’re connected to.
  5. As the pistons compress the air/fuel mixture in the cylinders, the plugs spark the air/fuel mixture.
  6. The air/fuel mixture explodes to create enough heat and pressure to power the engine.

The sound of the engine running is actually the spark plugs creating tiny explosions. The spark plugs ignite the air/fuel mixture about 400 times per minute, or 6 times a second. It’s a process so delicate that when a spark plug goes bad, the engine air/fuel mixture starts running too lean or rich. This results in decreased engine performance and increased fuel consumption.

Why do Spark Plugs go Bad?

Spark plugs typically go bad after some time due to several factors:

  • Carbon buildup from the air/fuel mixture burning inside the combustion chamber
  • Electrode erosion from the high temperatures caused by the sparks
  • Spark plug cables loosening up or wearing out over time

How Often Should Spark Plugs be Replaced?

Replace GM Plugs

Image Credit: PaulsTravelPictures

Spark plugs commonly go bad after about 50,000 miles. Some people choose to replace them in regular intervals or wait until the symptoms of a bad spark plug to crop up.

Replacing your spark plugs is pretty easy. You just need a few basic tools, OEM replacement spark plugs, and this replacement guide.

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