NAPA Engine Performance 4 — Questions and Answers
Question 1: A hot engine pings during acceleration. Which sensor lets the PCM retard timing to stop it?
- Camshaft position sensor
- Knock sensor (Correct answer)
- Crankshaft position sensor
- Intake air temperature sensor
Correct answer: Knock sensor
The piezoelectric knock sensor detects detonation vibrations so the PCM can retard spark timing.
Question 2: An engine cranks but will not start, and the tachometer reads zero while cranking. Which sensor is the most likely failure?
- Crankshaft position sensor (Correct answer)
- Throttle position sensor
- MAF sensor
- Coolant temperature sensor
Correct answer: Crankshaft position sensor
Without a crank position signal, the PCM sees no rpm and will not fire injectors or coils.
Question 3: When testing a coil-on-plug ignition coil, the most effective way to confirm a misfire follows the coil is what?
- Replace all spark plugs
- Swap the coil to another cylinder and see if the misfire moves (Correct answer)
- Check fuel pressure
- Perform a compression test first
Correct answer: Swap the coil to another cylinder and see if the misfire moves
If the misfire code moves to the new cylinder with the coil, the coil is confirmed faulty.
Question 4: A spark plug with dry, black, sooty deposits most likely indicates what?
- Oil burning past rings
- Rich mixture or weak spark (Correct answer)
- Overheating
- Normal wear
Correct answer: Rich mixture or weak spark
Dry carbon fouling is caused by a rich mixture, excessive idling, or weak ignition.
Question 5: A spark plug with blistered white insulator and melted electrodes indicates which condition?
- Cold plug heat range too low
- Overheating from lean mixture or overadvanced timing (Correct answer)
- Rich mixture
- Oil fouling
Correct answer: Overheating from lean mixture or overadvanced timing
Blistering and melted electrodes indicate excessive combustion temperature, often from lean mixture, advanced timing, or wrong heat range.
Question 6: Which reading on an ignition scope's firing line usually indicates high secondary resistance, such as an open plug wire?
- Very low firing voltage
- Very high firing voltage with a short spark line (Correct answer)
- Long spark line at low voltage
- Normal firing voltage with no coil oscillations
Correct answer: Very high firing voltage with a short spark line
High resistance in the secondary circuit takes more voltage to jump and leaves less energy for spark duration.
Question 7: A cam/crank correlation code (such as P0016) on a newly timed engine most likely means what?
- Timing belt or chain installed one or more teeth off (Correct answer)
- Faulty knock sensor
- Low fuel pressure
- Bad ignition coil
Correct answer: Timing belt or chain installed one or more teeth off
P0016 means the cam and crank signals are out of expected alignment, often from incorrect timing belt or chain installation.
