MTC Advanced Diagnostics & Troubleshooting 3 — Questions and Answers
Question 1: A technician performing a cylinder leak-down test finds 35% leakage with air escaping into the crankcase. This MOST likely indicates:
- A leaking intake valve
- Worn or broken piston rings (Correct answer)
- A blown head gasket
- A cracked cylinder head
Correct answer: Worn or broken piston rings
Air escaping into the crankcase during a leak-down test is the definitive indicator of ring sealing failure.
Question 2: On a two-stroke outboard, excessive carbon buildup on the power valves (YPVS/EXUP) typically causes:
- Hesitation and power loss in the mid-to-high RPM range (Correct answer)
- Difficulty starting when cold
- Oil injection system failure
- Overheating at idle
Correct answer: Hesitation and power loss in the mid-to-high RPM range
Power valves modify exhaust port timing; carbon restriction prevents them from opening fully, killing mid-to-high RPM power.
Question 3: Which test is the BEST method to confirm a faulty marine alternator versus a faulty voltage regulator?
- Check battery voltage at rest
- Perform a full-field bypass test on the alternator (Correct answer)
- Measure starter motor current draw
- Test battery specific gravity
Correct answer: Perform a full-field bypass test on the alternator
A full-field bypass directly energizes the rotor, isolating the regulator; if output rises, the regulator is faulty, not the alternator stator.
Question 4: A marine diesel engine's raw-water pump impeller fails frequently and prematurely. After replacing the impeller twice, the BEST next diagnostic step is:
- Replace the entire raw-water pump housing
- Inspect the raw-water strainer for blockage causing cavitation (Correct answer)
- Increase engine idle speed
- Flush the heat exchanger with acid
Correct answer: Inspect the raw-water strainer for blockage causing cavitation
A clogged strainer starves the impeller of water, causing cavitation-induced rapid wear or failure.
Question 5: A fuel injected marine engine fails to start after the vessel sat for two weeks. Live data shows injector pulse but fuel rail pressure drops to zero within 30 seconds of key-off. The MOST likely cause is:
- A faulty crankshaft position sensor
- A leaking fuel pressure regulator or check valve in the pump (Correct answer)
- A failed throttle body actuator
- A corroded fuel rail sensor
Correct answer: A leaking fuel pressure regulator or check valve in the pump
Rapid pressure bleed-down after key-off indicates the check valve in the pump or the pressure regulator is not holding residual pressure.
Question 6: During engine synchronization on a twin-engine vessel, the port engine surges at 2,200 RPM while the starboard runs smoothly. What is the FIRST system to inspect?
- Port engine ignition timing
- Port throttle cable stretch or binding causing irregular fuel delivery (Correct answer)
- Starboard fuel filter restriction
- Both engine mounts for softness
Correct answer: Port throttle cable stretch or binding causing irregular fuel delivery
A throttle cable that binds or has a flat spot can cause surging at specific RPM ranges by varying fuel delivery inconsistently.
Question 7: A vessel's hydraulic steering feels spongy and requires excessive effort to turn. After confirming adequate fluid level, the NEXT diagnostic step is:
- Replace the helm pump
- Bleed air from the hydraulic system starting at the cylinder ends (Correct answer)
- Inspect the rudder for fouling
- Flush and replace all hydraulic fluid immediately
Correct answer: Bleed air from the hydraulic system starting at the cylinder ends
Air trapped in hydraulic lines compresses, causing spongy feel; proper bleeding restores firm, responsive steering.
MTC Advanced Diagnostics & Troubleshooting 3
A technician performing a cylinder leak-down test finds 35% leakage with air escaping into the crankcase.
This MOST likely indicates: