ASE Engine Diagnostics 5 — Questions and Answers
Question 1: Right after a timing belt replacement, the engine sets a camshaft/crankshaft position correlation code. What is the most likely cause?
- Failed crankshaft position sensor
- Timing belt installed one or more teeth off (Correct answer)
- Low engine oil level
- Faulty PCM
Correct answer: Timing belt installed one or more teeth off
A correlation code after belt work usually means the cam and crank are out of time.
Question 2: During a power balance test, disabling cylinder 4 causes almost no rpm drop while the others drop about 100 rpm. What does this mean?
- Cylinder 4 is contributing little power (Correct answer)
- Cylinder 4 is the strongest cylinder
- The idle air control is faulty
- Ignition timing is too advanced
Correct answer: Cylinder 4 is contributing little power
A cylinder that already makes little power causes almost no rpm change when disabled.
Question 3: A spark plug has a white, blistered insulator tip. What does this indicate?
- Oil fouling
- Rich mixture
- Normal operation
- Overheating from a lean mixture or a plug heat range that is too hot (Correct answer)
Correct answer: Overheating from a lean mixture or a plug heat range that is too hot
Blistered white insulators result from excessive combustion chamber temperatures.
Question 4: A spark plug is covered in wet, black, oily deposits. What is the most likely cause?
- Overly advanced timing
- Oil entering the cylinder through worn rings or valve guides (Correct answer)
- Lean air-fuel mixture
- Plug heat range too hot
Correct answer: Oil entering the cylinder through worn rings or valve guides
Wet oily deposits mean engine oil is getting into the combustion chamber.
Question 5: An ECT sensor reports -40°F on a fully warm engine. Which symptom is most likely?
- Lean condition and pinging
- High idle with no other symptoms
- Rich running, poor fuel economy, and black smoke (Correct answer)
- Low oil pressure warning
Correct answer: Rich running, poor fuel economy, and black smoke
The PCM thinks the engine is cold and adds extra fuel, causing a rich condition.
Question 6: An engine cranks but will not start, with no spark and no injector pulse, and the tachometer reads zero while cranking. What is the most likely cause?
- Clogged fuel filter
- Failed single ignition coil
- Faulty crankshaft position sensor (Correct answer)
- Restricted air filter
Correct answer: Faulty crankshaft position sensor
Without a crank position signal, the PCM cannot fire the coils or pulse the injectors.
Question 7: When performing a cranking compression test, which step is correct?
- Hold the throttle wide open and disable fuel and ignition (Correct answer)
- Leave all other spark plugs installed
- Test the engine cold with the throttle closed
- Add oil to every cylinder before the first reading
Correct answer: Hold the throttle wide open and disable fuel and ignition
A wide-open throttle allows full airflow, and disabling fuel and ignition prevents flooding and coil damage.
ASE Engine Diagnostics 5
Right after a timing belt replacement, the engine sets a camshaft/crankshaft position correlation code.
What is the most likely cause?