ASE Engine Diagnostics 2

Question 1

A dry compression test shows two adjacent cylinders at 40 psi while all others read 160 psi. What is the most likely cause?

Accepted Answer

A blown head gasket between the two cylinders

Answer

Low compression in two adjacent cylinders usually means a failed head gasket between them.

Question 2

During a wet compression test, a low cylinder's reading rises significantly after adding oil. What does this indicate?

Accepted Answer

Worn or damaged piston rings

Answer

Oil temporarily seals the rings, so a big increase points to ring or cylinder wall wear.

Question 3

During a cylinder leakage test, air is heard escaping from the oil filler opening. Which component is leaking?

Accepted Answer

Piston rings

Answer

Air escaping into the crankcase means it is getting past the piston rings.

Question 4

During a cylinder leakage test, air is heard hissing from the throttle body. What is the likely fault?

Accepted Answer

Leaking intake valve

Answer

Air exiting through the intake system indicates the intake valve is not sealing.

Question 5

A vacuum gauge on a warm engine at idle shows a steady reading of 14 in. Hg instead of the normal 17–21 in. Hg. What is a likely cause?

Accepted Answer

Retarded ignition or valve timing

Answer

A steady but low vacuum reading typically indicates late ignition or valve timing.

ASE - Automotive Service Excellence Certified Tech Practice Test