Ignition Systems & Timing Flashcards
7 cards from real CPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Ignition Systems & Timing flashcards as text
What secondary voltage is typically required to fire a spark plug under normal compression in a gasoline engine?
Answer: 12,000–45,000 volts
Modern ignition systems must generate 12,000 to 45,000 volts in the secondary circuit to ionize the spark plug gap and fire reliably under the pressures and temperatures present in the combustion chamber.
What does the heat range of a spark plug indicate?
Answer: The plug's ability to transfer heat from its firing tip to the cylinder head
Heat range describes how quickly a spark plug transfers heat from its insulator tip into the cylinder head cooling system; a 'hotter' plug retains more heat, while a 'colder' plug dissipates heat faster.
What symptom is most commonly associated with ignition timing that is excessively retarded?
Answer: Loss of power, poor fuel economy, and excessive exhaust heat
Retarded timing causes combustion to occur too late in the power stroke, reducing the mechanical work extracted from the expanding gases and increasing exhaust temperatures as burning continues into the exhaust stroke.
What is a multi-spark discharge (MSD) ignition system designed to do?
Answer: Deliver multiple spark events during the compression stroke at low RPM to improve ignition reliability
MSD systems fire the spark plug multiple times per compression event at low engine speeds (typically below 3,000 RPM), ensuring complete combustion of the air-fuel mixture when crank rotation is slow enough to allow it.
What does the term 'total timing' refer to in performance engine tuning?
Answer: The sum of base timing and all forms of timing advance (centrifugal and vacuum)
Total timing is the combined ignition advance at a given operating condition, including the initial base timing plus all centrifugal and vacuum advance added by the distributor or ECU.
What is the purpose of vacuum advance on an older conventional ignition system?
Answer: To advance ignition timing during light-load, part-throttle cruise for improved fuel economy
Vacuum advance uses manifold vacuum (highest at light throttle cruise) to add additional timing advance during part-throttle operation, improving combustion efficiency and fuel economy when detonation risk is low.
How does an increased compression ratio generally affect ignition timing requirements?
Answer: Higher compression requires retarded timing or higher-octane fuel because the denser charge is more prone to detonation
A higher compression ratio creates greater heat and pressure in the combustion chamber, which makes the air-fuel mixture more susceptible to auto-ignition (detonation), requiring either retarded timing or higher-octane fuel to prevent knock.