Advanced Diagnostics & Troubleshooting Flashcards
7 cards from real MTC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Advanced Diagnostics & Troubleshooting flashcards as text
When diagnosing an intermittent no-start condition on a marine EFI engine, which diagnostic approach is most effective?
Answer: Capture live scan data during the failure event to compare against known-good values
Live data captured during the actual failure event provides direct evidence of which parameter is out of spec, avoiding guesswork.
A marine outboard overheats only at wide-open throttle but runs cool at cruise speeds. Which component failure BEST explains this pattern?
Answer: Partially blocked water jackets or a water pump impeller with missing vanes
A degraded impeller with missing vanes can move enough water at low demand but is overwhelmed at WOT, causing overheat only under high thermal load.
On a 4-stroke outboard with a wet sump oiling system, oil consumption is high but no external leaks are found. Exhaust is blue-gray under acceleration. The MOST probable cause is:
Answer: Worn valve stem seals or piston rings allowing oil into the combustion chamber
Blue-gray smoke during acceleration combined with high consumption and no external leaks is the textbook presentation of oil entering the combustion chamber via worn seals or rings.
A NMEA 2000 network on a vessel shows intermittent data dropouts on the chartplotter. The backbone appears properly terminated. What should the technician check next?
Answer: Backbone cable total length and individual T-connector seating and pin condition
Intermittent NMEA 2000 dropouts with proper termination usually stem from corroded or unseated T-connector pins or backbone length exceeding specification.
A technician notices the propeller on a stern-drive cavitates at high RPM. The engine reaches rated RPM easily. What is the MOST likely cause?
Answer: Air is being ingested at the propeller from a hull fitting, exhaust port, or through-hull above the prop
Air entrainment at the prop from nearby hull openings is the most common cause of cavitation that occurs specifically at high RPM when the engine otherwise performs correctly.
When performing a compression test on a diesel inboard, one cylinder reads 220 PSI while the remaining cylinders read 400–420 PSI. What is the MOST likely cause of the low reading?
Answer: A burned or bent exhaust valve, worn rings, or a head gasket failure on that cylinder
A single significantly low compression cylinder strongly points to a sealing failure — burned valve, blown head gasket section, or severely worn rings — rather than ancillary systems.
A marine DC electrical system experiences repeated circuit breaker trips on the bilge pump circuit. The bilge pump runs when manually tested at the pump terminals. What should the technician suspect?
Answer: A faulty bilge pump switch or float switch causing continuous duty operation
If the pump runs correctly but the breaker trips repeatedly, the pump is likely running continuously due to a stuck float switch, exceeding the breaker's thermal rating.