AERA Diagnostic & Troubleshooting Methods 3

Question 1

A vacuum gauge connected to the intake manifold shows a steady low reading of approximately 12–15 in-Hg at idle. What does this indicate?

Accepted Answer

Late ignition or valve timing

Answer

A steady but low vacuum reading at idle consistently points to retarded ignition timing or retarded valve timing affecting volumetric efficiency.

Question 2

When a cylinder leakdown test shows air escaping into the crankcase, what specific component failure is indicated?

Accepted Answer

Worn piston rings or cylinder walls

Answer

Air escaping into the crankcase (detectable at the oil fill cap or dipstick tube) during a leakdown test confirms worn piston rings or cylinder wall damage.

Question 3

What does a fluctuating oil pressure gauge reading during steady engine operation MOST often indicate?

Accepted Answer

Air in the oil due to a low oil level or foaming

Answer

A fluctuating oil pressure gauge typically indicates air entrainment in the oil caused by low oil level, aerated oil, or a cracked pickup tube drawing air.

Question 4

An engine produces a deep, rhythmic knock that is most pronounced at light throttle and disappears under heavy load. This is MOST characteristic of:

Accepted Answer

Piston slap

Answer

Piston slap is typically loudest at light load when combustion pressure is insufficient to hold the piston against the cylinder wall, and often diminishes under heavy load.

Question 5

After a valve job, an engine runs rough and has low power. A leakdown test shows 5% leakage on all cylinders. What is the MOST likely cause of the symptoms?

Accepted Answer

Excessive valve lash set on all cylinders

Answer

With acceptable ring seal (low leakdown), excessive valve lash on all cylinders after a valve job would cause rough running and power loss by reducing effective lift and duration.

(AERA) Automotive Engine Rebuilders Association Certification Practice Test

(AERA) Automotive Engine Rebuilders Association Certification Practice Test

AERA Diagnostic & Troubleshooting Methods 3