Engine Performance & Tuning 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 Engine Performance & Tuning flashcards as text
A marine technician is performing an ignition timing check on an older carbureted engine. The timing must be set with the vacuum advance:
Answer: Disconnected and plugged at the specified idle RPM
Base ignition timing is set with the vacuum advance disconnected and plugged so only mechanical timing advance affects the reading at the specified idle RPM.
What is the effect of installing a thermostat with a higher temperature rating than specified in a marine engine?
Answer: Engine runs hotter, potentially causing detonation and damage
A higher-rated thermostat keeps the engine at a higher operating temperature than designed, which can lead to detonation, increased wear, and potential overheating.
During a marine engine tune-up, spark plug inspection reveals deposits that are white and blistered. This indicates:
Answer: Overheating or too-lean mixture
White, blistered spark plug electrodes and insulators indicate the plug is running too hot due to engine overheating, pre-ignition, or a lean air/fuel mixture.
A marine diesel engine produces blue-white smoke at startup that clears when warm. The MOST likely cause is:
Answer: Worn valve stem seals allowing oil to enter the combustion chamber
Worn valve stem seals allow oil to drain down the valve stems into the cylinder during shutdown, burning off as blue-white smoke on startup until the engine warms.
What does a 'misfire detected on cylinder 3' (P0303) DTC indicate a technician should check FIRST?
Answer: Spark plug, ignition coil, and fuel injector on cylinder 3
A cylinder-specific misfire code directs the technician to inspect components directly responsible for combustion in that cylinder: spark plug, coil, and injector.
On a marine EFI engine, the long-term fuel trim (LTFT) reads +22%. What does this indicate?
Answer: The engine is running lean and the ECM is adding fuel to compensate
A positive LTFT of +22% means the ECM is adding 22% more fuel than the base map to maintain stoichiometry, indicating the engine is running lean.
When checking compression on a marine engine, one cylinder reads 90 psi while the others read 165 psi. After adding oil through the spark plug hole, compression rises to 150 psi. What does this indicate?
Answer: Worn or broken piston rings in that cylinder
When adding oil temporarily seals the rings and restores compression, the low reading is caused by worn or broken piston rings rather than a valve or head gasket problem.