CPT Ignition Systems & Timing 1 — Questions and Answers
Question 1: What does ignition timing refer to in an internal combustion engine?
- The moment the spark plug fires relative to piston position (Correct answer)
- The interval between fuel injection and combustion
- The delay between throttle input and engine response
- The time required for the engine to reach operating temperature
Correct answer: The moment the spark plug fires relative to piston position
Ignition timing refers to the precise moment the spark plug fires in relation to piston position, typically expressed in degrees before or after top dead center (TDC).
Question 2: What is the primary purpose of an ignition timing advance mechanism?
- To increase fuel economy at idle
- To allow combustion to complete optimally as engine speed increases (Correct answer)
- To reduce exhaust gas temperatures under load
- To synchronize the fuel injectors with valve timing
Correct answer: To allow combustion to complete optimally as engine speed increases
As engine RPM increases, combustion must begin earlier (advance) so the expanding gases reach peak pressure at the optimal piston position, maximizing power output.
Question 3: Which tool is used to dynamically measure ignition timing on a running engine?
- Vacuum gauge
- Timing light (stroboscope) (Correct answer)
- Multimeter
- Compression tester
Correct answer: Timing light (stroboscope)
A timing light uses strobe flashes triggered by the ignition signal to freeze the timing mark on the crankshaft pulley, allowing technicians to read dynamic timing while the engine runs.
Question 4: What is engine knock (detonation) in relation to ignition timing?
- Normal combustion noise at idle speed
- Uncontrolled ignition of the air-fuel mixture before or simultaneously with the spark (Correct answer)
- Mechanical noise from loose valve train components
- Fuel injector pulse noise heard under load
Correct answer: Uncontrolled ignition of the air-fuel mixture before or simultaneously with the spark
Detonation occurs when the air-fuel mixture auto-ignites due to heat and pressure rather than the spark, creating a sharp pressure wave that produces a knocking sound and can damage engine components.
Question 5: What is the difference between static timing and dynamic timing?
- Static timing is measured with the engine off; dynamic timing is measured with the engine running (Correct answer)
- Static timing applies to diesel engines; dynamic timing applies to gasoline engines
- Static timing uses a timing light; dynamic timing uses a scan tool
- Static timing is measured in milliseconds; dynamic timing is measured in degrees
Correct answer: Static timing is measured with the engine off; dynamic timing is measured with the engine running
Static timing is set with the engine off using a reference mark, while dynamic timing is checked with the engine running using a timing light to account for centrifugal and vacuum advance.
Question 6: What is the primary function of a distributor cap in a conventional ignition system?
- To regulate voltage to each spark plug in firing order sequence (Correct answer)
- To advance ignition timing based on engine load
- To convert primary voltage to secondary high voltage
- To control dwell angle for the ignition points
Correct answer: To regulate voltage to each spark plug in firing order sequence
The distributor cap routes the high-voltage secondary current from the coil to each spark plug wire in the correct firing order sequence as the rotor spins inside.
Question 7: What is a primary advantage of a distributorless ignition system (DIS) over a conventional distributor-based system?
- DIS systems require more frequent maintenance intervals
- DIS eliminates mechanical wear points and allows individual cylinder timing control (Correct answer)
- DIS systems use lower secondary voltage for improved safety
- DIS requires a physical timing belt to synchronize spark delivery
Correct answer: DIS eliminates mechanical wear points and allows individual cylinder timing control
Distributorless ignition systems remove the mechanical distributor, eliminating wear on the cap and rotor, while also enabling the ECU to control timing on a per-cylinder basis for optimized performance.
CPT Ignition Systems & Timing 1
What does ignition timing refer to in an internal combustion engine?