CPT Ignition Systems & Timing 2 — Questions and Answers
Question 1: What is dwell angle in a conventional points-type ignition system?
- The number of degrees the crankshaft rotates between spark events
- The number of degrees the distributor cam rotates while the points remain closed (Correct answer)
- The angle at which the distributor rotor aligns with the cap terminal
- The degrees of vacuum advance applied at cruise conditions
Correct answer: The number of degrees the distributor cam rotates while the points remain closed
Dwell angle is the number of degrees the distributor cam rotates while the contact points remain closed, allowing the ignition coil's primary circuit to build magnetic field energy before firing.
Question 2: What advantage does a coil-on-plug (COP) ignition system offer over a conventional single-coil system?
- COP systems require a shared secondary wire harness for simplified wiring
- Each cylinder gets a dedicated coil, providing maximum energy and faster recharge time (Correct answer)
- COP systems eliminate the need for a crankshaft position sensor
- COP systems use lower voltage to reduce insulation requirements
Correct answer: Each cylinder gets a dedicated coil, providing maximum energy and faster recharge time
Coil-on-plug systems dedicate one ignition coil per cylinder, allowing each coil maximum saturation time independent of engine speed and delivering higher, more consistent spark energy.
Question 3: What is the primary role of a crankshaft position sensor (CKP) in a modern ignition system?
- To measure exhaust backpressure for timing correction
- To provide the ECU with engine speed and piston position data for spark timing (Correct answer)
- To signal the fuel pump relay when cranking
- To measure crankshaft endplay for bearing wear detection
Correct answer: To provide the ECU with engine speed and piston position data for spark timing
The crankshaft position sensor sends a signal indicating the exact rotational position and speed of the crankshaft, which the ECU uses to calculate precise ignition timing for each cylinder.
Question 4: How does pre-ignition differ from detonation?
- Pre-ignition is caused by lean mixtures; detonation is caused by rich mixtures
- Pre-ignition occurs before the spark fires; detonation occurs after the spark fires (Correct answer)
- Pre-ignition only occurs at idle; detonation only occurs under full load
- Pre-ignition is harmless; detonation always causes immediate engine damage
Correct answer: Pre-ignition occurs before the spark fires; detonation occurs after the spark fires
Pre-ignition is caused by a hot spot (such as a glowing carbon deposit) igniting the mixture before the spark plug fires, while detonation is the spontaneous ignition of the end-gas charge after the spark has already fired.
Question 5: How does higher altitude generally affect ignition timing requirements?
- Higher altitude requires more retarded timing due to increased oxygen density
- Higher altitude typically requires more advanced timing due to lower air density and slower flame speed (Correct answer)
- Altitude has no measurable effect on optimal ignition timing
- Higher altitude requires timing retard to compensate for increased detonation risk
Correct answer: Higher altitude typically requires more advanced timing due to lower air density and slower flame speed
At higher altitudes, the lower air density reduces the likelihood of detonation and slows flame propagation, generally allowing and requiring more ignition advance for optimal combustion efficiency.
Question 6: What is the primary function of a knock sensor in a modern engine management system?
- To detect valve train noise and alert the driver via the check engine light
- To detect detonation and signal the ECU to retard ignition timing (Correct answer)
- To monitor combustion chamber pressure for misfire detection
- To adjust fuel trim in response to exhaust oxygen levels
Correct answer: To detect detonation and signal the ECU to retard ignition timing
The knock sensor detects the high-frequency vibrations characteristic of detonation and sends a signal to the ECU, which retards ignition timing to eliminate the knock and protect the engine.
Question 7: Why is the firing order of an engine important for performance technicians?
- It determines the oil viscosity required for proper lubrication
- It ensures that power strokes are evenly spaced to minimize vibration and heat buildup in adjacent cylinders (Correct answer)
- It sets the maximum RPM limit of the engine
- It defines the sequence in which valves open relative to the camshaft lobe profile
Correct answer: It ensures that power strokes are evenly spaced to minimize vibration and heat buildup in adjacent cylinders
The firing order is engineered to distribute power strokes evenly around the crankshaft and prevent adjacent cylinders from firing consecutively, which reduces vibration and avoids heat concentration in one area of the engine.
CPT Ignition Systems & Timing 2
What is dwell angle in a conventional points-type ignition system?