Auto Repair Encyclopedia
Ignition Cap and Rotor
Sometimes referred to as Ignition Cap and Rotor, Ignition Cap, Replace Cap, Replace Ignition Cap, Ignition Cap Replace, Cap Replace
The ignition (or distributor) cap and rotor are housed in the vehicle's ignition system. As part of the ignition distributor, they allow each spark to be "distributed" from the ignition coil to the ignition wires and then to each spark plug.
When the engine is running, high voltage created by the ignition coil travels to the ignition cap and then through the coil wire and ignition rotor. As the ignition rotor turns in the distributor, the rotor distributes the spark by sending it in a synchronized order through the spark plug wires to the spark plugs, located in each of the engine's cylinders.
Depending on the type of ignition system, the spark can range from 12,000 to 45,000 volts. Due to the high voltage, it’s critical that ignition system components are well-insulated. If insulation breaks down, the spark never arrives at the spark plug, causing the engine to run poorly—or not at all.
Be sure to inspect and/or replace the cap and rotor every 30,000 miles to avoid engine drivability problems.
Note: Engines utilizing multiple coil packs—also known as a coil-on-plug (COP) ignition—do not use an ignition distributor.
About this Repair: Ignition Cap and Rotor Replacement
Recommendations
The ignition cap and rotor should always be replaced as a set.
Why this happens
Ignition cap and rotor failure can be caused by failures elsewhere in the ignition system. The ignition wires and spark plugs should be thoroughly inspected. Old plugs or wires will burn out even a new cap and rotor.
Engine fluid leaks can cause damage to the ignition cap and rotor. These leaks should be repaired when the cap and rotor are replaced.
A failing ignition cap and rotor can cause hard starting, rough idling and poor acceleration. It can also cause the "Check Engine Light" to be lit. Continuing to drive with a bad cap and rotor can cause engine misfiring, which can damage the catalytic converter.
