NAPA Engine Repair and Diagnosis 2

Question 1

A cylinder reads 95 psi on a dry compression test and 140 psi after adding a teaspoon of oil. What is the most likely cause?

Accepted Answer

Worn or stuck piston rings

Answer

Oil temporarily seals worn rings, so a large rise on the wet test points to ring or cylinder wall wear.

Question 2

Two adjacent cylinders both show low compression of similar values while all others are normal. What is the most likely cause?

Accepted Answer

Head gasket failure between the two cylinders

Answer

A gasket breach between neighboring cylinders lets pressure escape from one to the other, lowering both.

Question 3

During a cylinder leakage test, air is heard escaping from the oil filler opening. Where is the leak?

Accepted Answer

Piston rings

Answer

Air passing the rings enters the crankcase and exits through the oil fill or PCV openings.

Question 4

During a leak-down test, air is heard hissing at the throttle body. Which component is leaking?

Accepted Answer

Intake valve

Answer

A leaking intake valve sends air back into the intake manifold and out the throttle body.

Question 5

Air escaping from the tailpipe during a cylinder leakage test indicates which problem?

Accepted Answer

Leaking exhaust valve

Answer

A poorly sealing exhaust valve lets test air pass into the exhaust system.

NAPA - National Automotive Parts Association Certified Mechanic Practice Test