What Is A Spark Plug And How Does It Work?

One of the biggest key players in the internal combustion process is a set of spark plugs. There’s one spark plug in each cylinder, and it provides the “spark” that’s needed to start the engine.

What Does A Subaru Spark Plug Look Like?

New OEM Subaru spark plugs

A spark plug is a small tube-shaped electrical part that’s composed of the following components:

  • Terminal that’s connected to the ignition coil
  • A central electrode
  • A ground electrode
  • Insulator that keeps all the electrical current inside the plug
  • A threaded housing that protects all the other components inside, and allows the spark plug to be screwed into the cylinder head.

The spark plug is screwed into each cylinder, and it’s connected an ignition coil. Connected to the ignition coil is the distributor (commonly in older cars) or the ECU (commonly in newer cars).

How A Spark Plug Works

Along with all the other spark plugs in the engine, a spark plug ignites the air/fuel mixture. When you turn the ignition key, a whole chain of events is kicked into motion, and your engine is fired up within a millisecond. The chain of events is as follows:

  1. The ECU signals the piston to suck the right mixture of fuel and air into the combustion chamber.
  2. The ECU also signals the battery to send electrical energy to the ECU or distributor.
  3. The distributor or ECU triggers the ignition coil(s) to release the energy they have stored.
  4. The ignition coil(s) amplify the electrical voltage before sending it to the spark plugs.
  5. Each spark plug converts the high voltage electrical energy into a spark.
  6. The spark ignites the fuel/air mixture, creating a tiny explosion.
  7. All the tiny explosions occur in a particular order determined by the ECU (or distributor), which keeps the engine running smoothly.

This process sounds pretty complicated, but it’s actually quite quick. In fact, it happens thousands of times per minute. Considering how delicate the entire process is, one malfunctioning spark plug can throw the entire thing out of whack.

How A Fouled Spark Plug Affects Your Engine’s Performance

Worn spark plugs

Image Credit: CarsNToys

Spark plugs wear out over time. When one of your spark plugs finally gives out, you’ll notice a reduction in engine performance and an increase in fuel consumption. This is because the cylinder with the bad plug isn't producing as much power as it should. To compensate, you have to give the car more gas to get the performance you were expecting. Also, the tune of the car is affected, and the engine will be less efficient even if you are gentle on the gas.

If you want optimal engine performance and fuel economy, replace your bad spark plug as soon as possible.

Diagnosing And Replacing A Fouled Spark Plug

The good news is that you don’t have to bring your Subaru to a dealership to diagnose or replace a bad spark plug. You can tackle both jobs right in your garage. To diagnose a bad spark plug in your Subaru, follow the steps outlined in this diagnostic guide.

If you’ve determined that one of your spark plugs needs to be replaced, you can buy a genuine OEM replacement spark plug from us at wholesale pricing. Here’s a comprehensive tutorial on replacing a spark plug in your Subaru.