Diagnostic & Troubleshooting Methods Flashcards
7 cards from real AERA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Diagnostic & Troubleshooting Methods flashcards as text
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?
Answer: Late ignition or valve timing
A steady but low vacuum reading at idle consistently points to retarded ignition timing or retarded valve timing affecting volumetric efficiency.
When a cylinder leakdown test shows air escaping into the crankcase, what specific component failure is indicated?
Answer: Worn piston rings or cylinder walls
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.
What does a fluctuating oil pressure gauge reading during steady engine operation MOST often indicate?
Answer: Air in the oil due to a low oil level or foaming
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.
An engine produces a deep, rhythmic knock that is most pronounced at light throttle and disappears under heavy load. This is MOST characteristic of:
Answer: Piston slap
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.
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?
Answer: Excessive valve lash set on all cylinders
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.
A technician suspects a cracked engine block. Which test is MOST definitive for detecting an internal crack that communicates between a water jacket and an oil gallery?
Answer: Pressure testing both systems simultaneously and cross-checking for leaks
Simultaneously pressurizing both the oil and coolant systems then checking for cross-contamination or pressure loss in each is the most definitive method for locating a communicating crack.
An engine emits blue-gray smoke under deceleration but not during acceleration. Which condition MOST likely explains this pattern?
Answer: Leaking valve stem seals
Leaking valve stem seals allow oil to be drawn past the valve stems during the high intake vacuum generated on deceleration, producing blue smoke specifically on decel.