Practice Test Geeks(MST) Marine Service Technician Practice Test
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Marine Engine Diagnostics & Repair Flashcards

7 cards from real MST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Marine Engine Diagnostics & Repair flashcards as text

  1. A marine technician performs a compression test on a 4-cylinder engine and finds cylinders 2 and 3 have equally low readings. What is the most likely cause?

    Answer: Blown head gasket between cylinders 2 and 3

    Adjacent cylinders with equally low compression indicate a blown head gasket between those cylinders, allowing combustion pressure to leak between them.

  2. What is the correct procedure for checking injector spray pattern on a port-fuel injected marine engine?

    Answer: Remove injectors and test on a bench injector tester

    Bench testing removed injectors on an injector tester allows direct visual inspection of spray pattern, atomization quality, and leak-down rate.

  3. An inboard marine engine vibrates severely at all RPMs. The engine mounts appear good. What should the technician inspect next?

    Answer: Propeller for damage or imbalance

    A damaged, bent, or imbalanced propeller is a leading cause of whole-RPM-range vibration in inboard installations after engine mounts are verified good.

  4. When rebuilding a marine engine, bearing clearances are checked using Plastigage. The measured clearance is 0.001 inches but the specification is 0.0015–0.003 inches. What should the technician do?

    Answer: Install a thinner bearing insert to increase clearance

    A clearance below specification creates insufficient oil film; installing a thinner bearing insert increases the running clearance to within the specified range.

  5. A marine diesel engine cranks normally but will not start in cold weather. The glow plug indicator light functions properly. What should the technician check first?

    Answer: Individual glow plug resistance with an ohmmeter

    A functioning glow plug light only indicates the circuit is energized; measuring individual glow plug resistance identifies failed elements that won't heat the pre-combustion chamber.

  6. Which condition would cause a marine engine's oil pressure gauge to read high at idle but drop to normal at higher RPMs?

    Answer: Stuck closed oil pressure relief valve

    A stuck closed oil pressure relief valve prevents excess pressure from being bypassed, causing artificially high pressure at idle that can normalize as pump output increases with RPM.

  7. A technician is diagnosing a fuel-injected outboard that runs rough and has a lean misfire code. Fuel pressure is within spec. What is the next logical diagnostic step?

    Answer: Check for vacuum leaks in the intake manifold

    Lean misfire with correct fuel pressure suggests unmetered air entering the intake; vacuum leaks allow air to bypass the throttle and MAF sensor, causing a lean condition.