ASE4 General Engine Diagnosis 2

Question 1

An engine has a wet compression test reading significantly higher than the dry test. This indicates:

Accepted Answer

Worn or damaged piston rings

Answer

Adding oil temporarily seals worn rings, causing a wet reading much higher than the dry reading.

Question 2

A vacuum gauge needle fluctuates between 14 and 19 in-Hg at idle. This suggests:

Accepted Answer

An intermittent misfire or sticking valve

Answer

A fluctuating vacuum needle at idle indicates an intermittent problem such as a sticking valve or random misfire.

Question 3

During a cylinder balance test, disabling cylinder #5 drops RPM by 50 while all others drop by 200. This indicates:

Accepted Answer

#5 is weak and contributing less power

Answer

A smaller RPM drop on one cylinder compared to others means that cylinder is contributing less power than the rest.

Question 4

A technician hears a rhythmic tapping noise that increases with engine speed. Oil pressure is normal. The MOST likely cause is:

Accepted Answer

Excessive valve clearance

Answer

Excessive valve clearance creates a rhythmic tapping that speeds up with engine RPM and is unaffected by oil pressure.

Question 5

A customer reports an engine knock that worsens under load but disappears at idle. This MOST likely indicates:

Accepted Answer

Rod bearing knock

Answer

Rod bearing knock intensifies under load because increased combustion pressure amplifies the bearing clearance impact.

ASE4 - ASE Automobile Engine Performance Practice Test