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ASE P2 Test Preparation Guide: Ignition System

ASE P2 Test Preparation Guide: Ignition System


Sample Review Questions:
1. Which of the following components generates a timing trigger signal for the ignition system?
a. Crankshaft position sensor
b. Ignition module
c. Ignition coil
d. Rotor

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2. Counterman A says a Coil-On-Plug (COP) ignition system has one ignition coil for every pair of spark plugs. Counterman B says a “Waste Spark” ignition system does not use a distributor, rotor or spark plug wires.  Who is right?
a. Counterman A only
b. Counterman B only
c. Both Counterman A and B
d. Neither one

3. A spark plug’s “heat range” can be determined by:
a. Its part number
b. Measuring the length of the spark plug
c. Measuring the diameter of the spark plug
d. Measuring the electrode gap


4. All of the following about iridium spark plugs is true EXCEPT:
a. The electrode gap is different than an ordinary spark plug
b. They usually have a single ground electrode
c. They typically have a smaller diameter center electrode than ordinary spark plugs
d. They have a service life of 100,000 miles or more

1A, 2D, 3A, 4A

1. The Crankshaft Position Sensor (CKP) may be mounted on the front, side or rear of the engine. The sensor reads notches in the crankshaft balancer, crankshaft or flywheel to generate a timing signal for the PCM and ignition system. There are two basic types of crank sensors: magnetic and Hall effect. Loss of the sensor signal will prevent the engine from starting (no spark). In older engines with distributors, a magnetic or Hall effect pickup in the distributor generates a trigger signal for the ignition module to fire the ignition coil. A bad pickup or damaged wiring can cause a no spark condition.


2. Coil-on-plug ignition systems have one coil per spark plug, mounted directly over the spark plugs. No spark plug wires are used.

Some distributorless ignition systems (DIS) are “waste spark” systems, meaning one coil fires two spark plugs simultaneously. The shared plugs are opposite each other in the engine’s firing order, so the second plug fires during the exhaust stroke and does nothing. The advantage with the waste spark approach is that it reduces the number of individual coils in the ignition system by half. The disadvantage is the waste spark accelerates electrode wear in the spark plugs unless double platinum or iridium spark plugs are used.


3. The “heat range” (operating temperature) of a spark plug depends on the internal design of the center electrode, the distance heat has to travel inside the plug from the electrode to the metal shell and the conductivity of the center electrode. Copper core center electrodes are often used to increase thermal conductivity and provide a broader heat range.

If a spark plug is too cold for an engine application, it may experience fouling and misfiring problems. If a spark plug is too hot for an engine application, it may become a source of pre-ignition/detonation when the engine is under load.


The heat range is determined by the spark plug manufacturer with engine testing, and is encoded in the spark plug number. You can use a heat range reference chart to look up hotter or colder spark plugs within a brand line, or use a cross-reference chart to look up other brand spark plugs with a similar heat range.

4. Iridium spark plugs have a thin wire iridium center electrode. Like platinum plugs, they typically have a service life of 100,000 miles plus. Most iridium plugs have a single ground electrode, and the gap is set the same as a standard spark plug. Some platinum plugs have two or four ground electrodes and have a wide, nonadjustable surface gap design.

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