What do spark plugs do? Car spark plugs are devices that create a spark of electricity in the car engine to ignite the air-fuel mixture. It is this spark that starts the car engine. Car spark plugs are an essential component of the car engine, and they must be in good working order for the car to run properly. There are many different types of car spark plugs, and each type has its own specific function. Spark plugs can be made of different materials, and they can have different sizes and shapes. The most common type of car spark plug is the round, silver-colored plug with a small tip. These plugs are designed to create a strong spark that will Ignite the air-fuel mixture in the car engine. Car spark plugs typically need to be replaced every 30,000 miles or so, and it is important to use the correct type of plug for your car model. Incorrectly sized or shaped plugs can cause engine misfires and damage to the car engine.