Importance of good sparkplugs

In a gasoline engine the importance of good sparkplugs cannot be denied. The electrical arc between the electrode and the ground strap is like a miniature bolt of lightning that ignites the air fuel mixture and in turn generates the power that drives the wheels.

These miniature lightning bolts are commonly called sparkplug firing by most mechanics. If the sparkplug doesn’t fire, the engine doesn’t start. When diagnosing a no start condition some mechanics will say the reason the engine won’t start is because there is no fire.

It is the ignition system that produces the electrical energy that fires the plug. Spark also must be maintained long enough to allow complete combustion of the air fuel mixture in the cylinder. The ignition system then has to deliver this electrical energy to each sparkplug at the right time.

Ignition timing refers to the precise moment the spark occurs. The spark is required when the piston is heading up on the compression stroke and the right time to fire the plug is just before that piston reaches top dead center or TDC.

In many engines the initial timing is specified at a point between five and 20° before top dead center. To get the most performance out of the engine the ignition timing must change as operating conditions also change. Most engine timing changes are required as engine rpm and load changes.

The higher the engine rpm the more often the sparkplug needs to be fired. The ignition system needs to keep up with the changing engine conditions. This means the ignition system must be able to monitor the rotation of the crankshaft and the relative position of each piston so that it can deliver a high voltage surge at the proper time during the compression stroke.

On gasoline engines the high voltage surge that creates the spark comes from a coil. Most automotive ignition coils are capable of producing voltage of between 30,000 and 60,000 V. Which is pretty impressive considering that the vehicle’s battery is only 12 V?

The ignition coil steps up the voltage by multiplying the battery voltage. The process that it uses to multiply battery voltage is also what gives the ignition part its name. An ignition coil is just that. Inside are coils of wire that use a magnetic field to increase voltage.

The construction of the coil and the magic of the magnetic field allows the coil to output pulses or bursts of high voltage that are sent to the sparkplug to ignite the air fuel mixture on the compression stroke.

This is just a simplified general overview of how the spark is created and used to start and run your engine. Although not everybody needs to know this information it can come in handy when you’re trying to diagnose a no start condition.

You need three things for an engine to start. You need air, fuel and spark. If you are missing any of those three elements the result is a no start condition. If you find that it is the spark that is missing, all of your attention can focus on diagnosis and troubleshooting the no spark condition.

If you want to see what good and bad sparkplugs look like I have a video on my you fix cars website about replacing sparkplugs. For more of the latest auto repair posts on this site visit the blog auto repair page.