Copyright Goodheart-Willcox Co., Inc. Auto Fundamentals 210 On some newer engines, the COP coil core is magnetized to allow a smaller coil size that produces the same amount of voltage. These are long with a small diameter and are some- times called pencil ignition coils. Often these coils are used where clearances are tight, such as between two camshaft covers of a dual overhead camshaft engine. Some ignition systems with two plugs per cylinder use a dual coil assembly installed over the plugs. Dual Coil-on-Plug System The dual coil-on-plug ignition system is used on engines with two spark plugs per cylinder. Using two spark plugs per cylin- der increases combustion efficiency. The system has one coil per cylinder. The difference between this system and other COP systems is that each coil is installed directly over one plug, and is connected to another plug through a secondary wire. The second, or remote, plug is installed in a different cylinder. Figure 10-13 shows the coil assemblies installed on an engine. Every coil and plug fires during one crankshaft revolution. To reduce the energy needed from the coils, each coil fires one plug on the compression stroke and one plug on the exhaust stroke. This reduces the voltage needed to fire the plugs. Note The terminology used to describe ignition systems can be confusing. Remember that a distributorless system features multiple ignition coils since no distributor cap and rotor are installed in the system to distribute the spark from a single igni- tion coil. A feature necessary on all distributor ignition systems that is also used on some designs of distributorless systems (waste spark and coil-near-plug) is some type of conductor—secondary wires or conductor strips—between the ignition coil(s) and the spark plugs to carry the spark. A direct ignition (coil-on-plug or dual coil-on-plug) system, on the other hand, is a multi-coil, distributorless system that does not use conductors between the ignition coils and the sparks plugs. Instead, there is one coil mounted above each plug. Coil assemblies Spark plug Boot Coil assembly A B General Motors Figure 10-12. A—These direct ignition coil assemblies are installed on an inline engine. The wiring harness is not shown. B—A direct ignition coil assembly. Coil To remote plug Goodheart-Willcox Publisher Figure 10-13. The dual coil-on-plug system is used on engines with two plugs per cylinder.