It's All About Timing
All of an engine's systems are designed to work at an exact time in the combustion process. If something occurs that causes a problem during the process, the engine will begin to have problems that include low fuel efficiency, decreased power and misfires. If the problem isn't addressed, the engine won't turn over and a repair will be necessary.
Spark Plugs/Wires
The electrical charge generated by the battery, by way of a starter solenoid, ignites the air/fuel mixture that is contained in the combustion chamber. Each chamber contains a spark plug that takes in the electricity, sparking through the wires on the spark plugs. If the spark plugs and wires aren't maintained and kept in good shape, the vehicle will start to have performance problems. Whether you install the spark plugs yourself or have a professional do it, make sure that the spark plugs are properly gapped prior to installing them. Because the much needed spark is generated when an electric current jumps the "gap", it's important that it's processed correctly or the engine will run badly.
Additional problem areas relating to spark plugs include the deposit buildups on the electrode area which is one of the reasons it's so important to have them check out. Something that's useful to know is that hot plugs burn hotter, which means that they can burn off more of the deposits. Cold plugs are common in high-performance engines. You can determine what type of plug is installed by the vehicle make and model.
The best way to determine of a spark plug wire needs to be replaced is to start the vehicle in a dim/dark location. Check the wires out while the engine is running, along with the wires that run from the spark plug to the distributor cap. The dark lighting will make it possible to notice sparks in the system that are out of place. It's common to see tiny arcs of electricity jump from breaks and cracks located in worn out spark plug wires.
The Main Purpose of Ignition Coils
The ignition system's main purpose is to provide the engine with the appropriate spark, inducing a higher voltage from a low voltage, at the right time, allowing the fuel/air mixture in the combustion chamber to ignite. The design of conventional ignition coils is somewhat similar to a transformer and includes a laminated iron core that reinforces the magnetic field. The energy stored in the core's magnetic field is transferred to the spark plug. Besides the iron core, the primary components include the primary winding, secondary winding and electrical connections.
Rotor and Distributor Cap
The rotor system and cap are used by the distributor to "distribute" the high-voltage charge to the appropriate cylinder. As the rotor spins, it distributes the high voltage charge to the cylinders while it moves past each contact. The current arcs over the small gap in between the rotor and contact when they pass each other. Eventually, the high level of heat that is produced by the passage of the charge eventually will cause wear and tear, especially the rotor. This is why mechanics typically replace the rotor and distributor when they perform tune ups on older vehicles.
Engines Without a Distributor
Newer vehicles don't use a central distributor, instead using an ignition coil for each spark plug instead. Connected to the engine's computer, or ECU (Engine Control Unit), this increases the accuracy the vehicle control system when it comes to the timing of the spark plugs. It also improves power, fuel efficiency and reduces emissions.
Diesel Engines
Instead of using a spark plug, Diesel engines use compression to ignite the diesel fuel. During winter months, diesel engines use glow plugs to heat up a cold cylinder before starting the engine.