What Does a Spark Plug Do?

Your ignition system is pretty complex, and there are a number of important components that must work with one another to crank the engine and then keep it running. Your spark plugs are among the most important of these, and you have several of them (one per cylinder).

The job of your spark plugs

Spark plugs have a very simple yet essential job. They provide the spark necessary to ignite gasoline in the combustion chamber. Without working spark plugs, your engine will not run (there will be nothing to ignite the fuel and start the combustion process). Your car’s engine basically runs on a series of miniature, contained explosions. First, air and fuel are mixed in each cylinder. When the piston rises toward the top of the cylinder, the spark plug fires. Electricity arcs from the electrode to the tab, and the fuel and air mixture ignites. This creates pressure as the fuel is transformed into a gas (emissions), which pushes the piston back down and turns the engine. This cycle is repeated over and over again in each cylinder of your car.

The engine has one spark plug per cylinder. Each spark plug is connected to a spark plug wire (in conventional and electronic ignitions). The wire runs from the top of the plug to the distributor, which is attached to the coil. However, if you have a distributor-less ignition, you have no spark plug wires. Rather, coil packs are used and the whole system is controlled by the computer.

Over time, your spark plugs wear. This is completely normal. Eventually, they will need to be replaced. The primary form of wear is to the electrode – as the spark plug arcs, it loses tiny amounts of electrode material. Eventually, it shortens. When it becomes too short, it won’t arc properly and the engine will misfire.


The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How to Remove, Install, and Adjust Ignition Timing
Ignition distributors help spark the gas and air in the engine. Worn distributors need to be removed to be cleaned to maintain proper ignition timing.
How to Replace an Ignition Ignitor
The ignition ignitor sends a signal to supply power and start the engine. A common sign of failure is a disruption in the engine's starting process.
How to Troubleshoot a Car That Won't Turn Off
If your car won't turn off, inspect the power relay, idle speed, ignition timing, and spark plugs. Using premium fuel may help but isn't a solution.

Related questions

How I change the engine switch position with the key?
The engine switch has four positions: Off, ACC, On, and Start. When you insert the key, the switch will automatically be in the Off position. Rotate the key clockwise one position to reach the ACC position, where some electrical components...
My steering wheel locked now my car won't start
Hello. It sounds like you have a steering lock or ignition switch problem. Most of the time the switch fails which will turn the ignition off and lock the steering. I typically take the steering column apart to inspect the...
No crank no start
I have to agree with you. The reason why is that jiggling symptom you are describing to get radio power. There isn't a whole lot else that can explain that. It sounds like you have power but there is a...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com