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The Ignition System

The ignition system produces the spark necessary to ignite the air and fuel mixture in the engine cylinders. The ignition system has seen many redesigns over the years. The most drastic changes have occurred in the last fifteen years.

Types of ignition systems

  • Distributor
    • breaker point
    • electronic
  • Distributorless
  • Coil-on-plug or COP

Breaker point ignition system components include the following except the crankshaft sensor, pulley and ignition module.

Electronic distributor ignition systems substitute a stator for breaker points and include an ignition module.

Distributorless ignition systems include the following except the distributor, breaker points, capacitor, rotor, and distributor cap.

The most common ignition system found on cars manufactured today is the coil-on-plug system. This system is very efficient in terms of production, energy use, and maintenance. The COP ignition system has individual coils directly on top of the spark plugs, a crankshaft sensor and pulley, and ignition module.

Ignition system components

  • Ignition coil
  • Distributor
  • Breaker points
  • Capacitor
  • Rotor
  • Distributor cap
  • Ignition wires
  • Spark plugs
  • Crankshaft sensor
  • Crankshaft pulley
  • Ignition module

Ignition coil

The ignition coil generates the high voltage needed to ignite the air fuel mixture in the cylinders. It is usually mounted on the engine, firewall, or directly on top of the distributor.


The distributor is the hub for the distribution of the ignition spark. It is located on top of the engine in the front or rear. It may be mounted vertically or horizontally. The distributor has a gear that meshes with a gear on the camshaft. This connection is how the distributor shaft turns the rotor.

Breaker points

The breaker points interrupt the ground path of the electricity from the coil. The points are located inside the distributor. They open by means of a cam on the distributor or a vacuum servo. When the points open, they break the electrical ground for the ignition coil. The electricity then flows from the coil to the spark plugs. The points have specific adjustments.


The capacitor acts as an electrical shock absorber for the points. It is designed to prevent arcing and slow the wear of the breaker points.


The rotor serves as a path for the spark from the coil to the distributor cap. It sits on the top of the distributor shaft underneath the cap. The top middle of the rotor is connected to the coil wire terminal on the cap. As the rotor spins, the end of it makes contact with the terminals for each spark plug wire underneath the cap.

Distributor cap

The distributor cap provides a route for the electricity from the rotor to the wires. It is mounted to the top of the distributor. The spark plug wires and coil wire attach to the distributor cap.

Ignition or spark plug wires

The spark plug wires provide the path for electricity to flow from the coil to the distributor cap and from the distributor cap to the spark plugs. They are insulated and must be routed properly and separately.

Spark plugs

The spark plugs are the end of the line for the high voltage in the ignition system. The spark plugs are mounted on the cylinder head. The high voltage arcs across the gap from the electrode to the ground strap. This arcing produces a high voltage spark that ignites the air and fuel mixture in the cylinder.

Crankshaft sensor

The crankshaft sensor indicates the position of the piston in cylinder number one. The position of this piston when the spark occurs is very crucial. It is the reference for which the engine is timed. The crankshaft position sensor is typically a hall effect sensor.  It sends a signal to the ignition module indicating the position of cylinder one piston when it detects a missing tooth on the crankshaft pulley. Consequently the module knows when to apply power to the coil(s).

Crankshaft pulley

The crankshaft pulley provides a reference for the position of cylinder number one piston. The pulley can only be installed in one position and one direction.

Ignition module

In a coil-on-plug system the ignition module uses the information from the crankshaft sensor to switch the coils off and on at the appropriate time. The module may be integrated into the PCM, ECM or other module that controls the engine.

Ignition system timing

Ignition system timing refers to the moment when the spark at the spark plug occurs in relation to where the piston is in its travel. The ignition system must be set correctly for the engine to perform correctly. Ideally the spark will occur just before the piston reaches the apex of its travel. This will ensure that the air and fuel mixture is ignited properly and entirely. Timing of the ignition system in distributor ignition systems is achieved by rotating the distributor clockwise or counter clockwise. In all other systems timing is computer controlled and cannot be adjusted.

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