From Matthew Wright,
Your Guide to Auto Repair.
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Before we can fully understand how the ignition system on your car functions, we need to brush up on the basics of internal combustion.
Your engine is like a big pump. It pumps air and gas in, then pumps exhaust out. The byproduct is a lot of energy that is sent to your wheels (and exhaust out the tailpipe. That's the basic of all basic descriptions. A little detail helps complete the picture. Your engine mixes air and fuel, then adds a spark to make the explosion. This spark ignites the air-fuel mixture, and is referred to as the ignition.
This ignition takes place thanks to a group of components working together, otherwise known as the ignition system. The ignition system consists of an ignition coil, distributor, distributor cap, rotor, plug wires and spark plugs. Older systems used a points-and-condenser system in the distributor, newer (as in most we'll ever see anymore) use an ECU, a little brain in a box, to control the spark and make slight changes in ignition timing. What do all of these components do? We'll explain.