Spark plugs are one of the most important things on your engine and here’s why: Air and fuel are mixed inside the cylinders of your engine and at just the right moment the spark plugs fire, ignite the mixture and power is produced. But how does that spark get to the spark plug in the first place?

An ignition part called the coil produces the spark for the spark plug, which requires over 20,000 volts of electrical power. But then that energy needs to get from the coil to the spark plug.

Years ago, the coil sent the spark to what’s called a distributor cap through an insulated spark plug wire. Inside of the cap was a rotor, which would spin around, sending that spark out to the different cylinders through the spark plug wires. Although this was the best way to deliver the spark at the time, there were a lot of parts that the spark passed through on its way to the spark plug. If any of those parts failed, the spark could short circuit and never make it to the spark plug. That would cause the engine to stumble and run rough.

Here are some of the things that cause problems with the ignition system and the spark in the past:

Spark plug wires wear out due to the amount of heat under the hood and just plain wear and tear. When this happens, the plug wire can allow the spark to short out before reaching the spark plug. In that case, the fuel that was in that cylinder is wasted due to a lack of a spark.

On older vehicles, the distributor cap and rotor would wear out as well, causing the same types of problems. The spark plug itself can even cause problems. If it is worn out or cracked, you may not be getting a proper spark in the cylinders and the car will not run properly.

Newer vehicles are eliminating many of these problems by using fewer parts to deliver the spark to the plug. On many newer vehicles, each spark plug has its own coil and in many cases it’s mounted right on the spark plug itself.

Electronic sensors and the vehicle's computer now tell each individual coil when to fire, making engines run much more efficiently. All of this adds up to better performance, better gas mileage and less pollution.

If your car is running rough and the check engine light is on there is a chance that it’s related to the ignition system and the spark. But it could also be related to a number of other issues as well. So don’t just throw parts on without diagnosing what’s wrong. Doing that would just be a shot in the dark at fixing your spark.