Ignition components include spark plugs (usually one per engine cylinder, but some have two), spark plug wires (not used with coil-on-plug ignitions), ignition coils (single or multiple coils depending on the application), ignition module (if used), an ignition pickup (distributor systems) or a crankshaft position sensor (distributorless systems), and on older engines a distributor. The ignition switch also is part of the ignition circuit.
Distributorless Ignition Systems (DIS) include “waste spark” DIS systems with coil packs and plug wires, Coil-On-Plug (COP) ignitions (one coil per spark plug), and Coil-Near-Plug (CNP) ignitions (one coil per plug with a short plug wire between the plug and coil).
Maintenance requirements are minimal on most late engines with long-life 100,000 mile platinum or iridium spark plugs. Conventional spark plugs need to be changed every 45,000 miles, and can be upgraded to platinum or iridium for longer service life. Replacement spark plugs must have the same size, thread pitch, length as the original, but can be any brand or type of electrode. Always follow the supplier application lists for correct spark plug fitment. Plugs are pregapped, but the gap may have to be adjusted for the application.
On ignition systems that use plug wires, new plug wires are recommended on high-mileage vehicles. Plug wires should be replaced if resistance exceeds specifications, the insulation is damaged or burned, or the boots do not fit tightly. Plug wires can be replaced individually if damaged, but high-mileage plug wires should be replaced as a set. Replacing each wire one at a time avoids mixups in the firing order.
Ignition coils create high voltage to fire the spark plugs. Coils run hot and can fail from overheating, causing a weak spark or no spark. With COP ignition coils, cracks, moisture or contaminates on the coil tube that fits down over the spark plug may cause misfiring.
Distributorless ignition systems use a Crankshaft Position Sensor (CKP) to generate trigger and timing signals for the ignition system. The crank sensor may be located on the front, rear or side of the engine. It may read a notched wheel on the crank pulley, crankshaft or flywheel. The sensor may be a magnetic sensor or a Hall effect sensor. Magnetic sensors generate an alternating current (AC) signal that changes in frequency and amplitude with rpm. Hall effect switches produce an on-off digital voltage signal. A bad crank sensor can cause loss of spark, intermittent misfiring or a no start due to no spark. Some crank sensors require a special adjustment procedure when they are replaced.
Required to pass this section of the P2 test:
1. Identify major ignition system components and types of systems.
2. Identify component function and common reasons for replacement.
3. Identify related items and tools.
4. Provide basic use, maintenance, installation, and warranty information.