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9 e l There will be three questions on c r i

C the ASE P2 test that deal with ignition systems, parts and products.

ll gasoline engines have a spark ig- plugs and connect the coils to the plugs A nition system to ignite the air/fuel with short wires. mixture in the cylinders. The spark is Ignition coils come in various shapes created by a high-voltage surge from and sizes, but all do essentially the an . The coil is triggered by same thing: They are step-up trans- an ignition module and/or the PCM formers that convert 12 volts DC into using a signal from a distributor 7,000 to 40,000 or more volts DC. The pickup or position sensor. If actual voltage required to fire a spark the engine has a distributor, a single plug depends on engine speed, load, coil is used on most engines to supply temperature, resistance in the plug and high voltage to all the spark plugs (a wires, and the distance across the spark few Japanese applications use two plug electrodes. coils). If the engine has a “distributor- Inside the coil are two sets of copper less ignition system“ (DIS), each spark wire windings, one inside the other. If the coil windings short out or break, the coil may not produce enough volt- Automatic Transmission age to fire the spark plugs causing the Braking System engine to run rough or die. Hairline cracks in the coil housing or insulation Cooling System can also weaken or kill the spark. Coils can be tested by measuring their pri- Drivetrain mary and secondary resistance with an Electrical System ohmmeter or a spark tester. Replace- ment coils must be the same type as the Emission Control System original to match the engine’s voltage requirements. Engine Parts Electronic ignition systems all use and Seals some type of transistorized switching module to turn the coil(s) on and off. On some vehicles (GM and Ford), the module may be mounted on or in the Fuel System distributor. On DIS systems, it is often HVAC part of the coil pack assembly. Modules can be damaged by heat and vibration. Ignition System A module failure will usually cause a no-spark, no-start condition. GM High Manual Transmission/Transaxle Energy Ignition (HEI) modules in older Steering & Suspension vehicles require a thin layer of dielec- tric grease underneath to conduct heat away from the module. If your cus- plug has its own separate coil. On Gen- tomer forgets the grease, the module eral Motors’ “waste spark” DIS sys- may not live very long. tems, two spark plugs share the same Ignition modules may receive a trig- coil. Many newer vehicles have coils ger signal directly from a distributor that are mounted directly over the pickup (magnetic, Hall effect or opti- and use no plug wires. cal), a crankshaft position sensor or the These are called “coil-on-plug” (COP) PCM. A fault in any of these other com- ignition systems. Another variation is ponents or the wiring can prevent the “coil-near-plug” (CNP) systems that ignition system from firing. Accurate mount individual coils near the spark diagnosis is essential to prevent unnec-

94 COUNTERMAN OCTOBER 2007 www.counterman.com essary parts replacements and returns. avoid mixing up the ). Re- cause pre-ignition. Many spark plugs If a vehicle has a distributor, the cap placement is needed if internal resist- have a “copper core” center electrode and rotor may develop carbon tracks ance in the wires exceeds that improves heat conduction and and cracks over time. This can lead to specifications, the wiring is damaged, gives the plug a broader operating ignition misfire and hard starting. Re- or the plug boots or terminals fit poorly range. placing the cap and rotor when the or are loose. Spark plugs are designed for specific spark plugs are changed is often neces- Finally, we come to the business end engines. The diameter, length and sary to restore “like-new” ignition per- of the ignition system: the spark plugs. pitch of the threads that screw into the formance. Spark plugs come in different sizes, head must match the applica- Plug wires connect the distributor or lengths, threads and electrode config- tion. How far the tip of the spark plug individual coils to the spark plugs. Also urations, but all have some type of extends into the called ignition cables, they come in var- center electrode surrounded by a ce- (called “reach”) must also be correct ious types (suppression and solid core ramic insulator in a threaded steel for the application, otherwise the tip of — also called “mag” wires) and with shell. Most long-life spark plugs have the plug may hit the or valves. various types and grades of insulation electrodes made of platinum or irid- Always follow the spark plug listings and jacketing (silicone, EPDM and ium and have a service life of 100,000 in your plug supplier’s catalog. other materials). The higher the tem- miles. The “heat range” (operating The distance across the electrode perature resistance of the insulation temperature) of a spark plug depends gap at the end of the spark plug must and jacketing, the better. Cable diame- on the length and shape of the ceramic also be set to certain specifications for ters are usually 7 or 8 mm and each insulator. The spark plug has to run the engine to run properly. If the gap is cable is a different length to fit specific hot enough so fuel deposits don’t too narrow, the spark may not be long spark plugs. Replacement cables must build up on the tip, foul the electrode enough to ignite the fuel mixture reli- be the same size and length as the orig- and cause it to misfire. But it also has ably, resulting in ignition misfire. If the inal. Plug wires may be replaced indi- to conduct enough heat away from gap is too wide, there may not be vidually or in complete sets (wires the tip so the tip doesn’t get too hot enough available voltage to create a should be changed one at a time to when the engine is under load and spark, also causing ignition misfire. t d r a C n o 6 9 e l c r i C

96 COUNTERMAN OCTOBER 2007 www.counterman.com