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
A four-stroke outboard engine cranks but will not fire. Spark is confirmed at all cylinders. What is the MOST logical next diagnostic step?
Answer: Verify fuel pressure and injector pulse signal
When spark is confirmed, the next step is to verify fuel delivery — pressure and injector operation — before moving to mechanical checks.
Which symptom most strongly indicates a cracked engine block in a marine inboard?
Answer: Coolant level that drops without visible external leaks
A cracked block allows coolant to migrate internally without visible puddles, causing a steady unexplained coolant loss.
A stern-drive unit vibrates heavily at speeds above 3,000 RPM but is smooth at idle. The most likely cause is:
Answer: A damaged or out-of-balance propeller
Propeller imbalance or damage creates centrifugal vibration that intensifies with RPM, not present at low speeds.
When diagnosing an EFI marine engine with a lean misfire fault code, the technician should first inspect:
Answer: Mass air flow sensor output and vacuum lines for leaks
Vacuum leaks and MAF errors both introduce unmetered air, causing a lean condition before suspecting fuel-side components.
A marine battery bank shows 12.6 V at rest but collapses to 9.8 V under starter load. This indicates:
Answer: Sulfated or failed battery cells with high internal resistance
Healthy batteries maintain near-resting voltage under load; severe voltage drop under cranking load is the classic sign of internal cell failure or sulfation.
An inboard diesel exhibits black smoke at all throttle positions. Which condition is LEAST likely to cause this symptom?
Answer: Low coolant temperature from a stuck-open thermostat
A stuck-open thermostat causes long warm-up and may affect performance but does not directly cause continuous black smoke.
When using a vacuum gauge to diagnose an inboard gasoline engine, a needle that oscillates widely between 14 and 20 in-Hg at idle most likely indicates:
Answer: A leaking head gasket on one or more cylinders
Wide, rhythmic vacuum oscillation at idle is the classic gauge signature of a leaking head gasket allowing intermittent combustion pressure into the intake manifold.