MTC Engine Performance & Tuning 5

Question 1

A marine technician is performing an ignition timing check on an older carbureted engine. The timing must be set with the vacuum advance:

Accepted Answer

Disconnected and plugged at the specified idle RPM

Answer

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.

Question 2

What is the effect of installing a thermostat with a higher temperature rating than specified in a marine engine?

Accepted Answer

Engine runs hotter, potentially causing detonation and damage

Answer

A higher-rated thermostat keeps the engine at a higher operating temperature than designed, which can lead to detonation, increased wear, and potential overheating.

Question 3

During a marine engine tune-up, spark plug inspection reveals deposits that are white and blistered. This indicates:

Accepted Answer

Overheating or too-lean mixture

Answer

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.

Question 4

A marine diesel engine produces blue-white smoke at startup that clears when warm. The MOST likely cause is:

Accepted Answer

Worn valve stem seals allowing oil to enter the combustion chamber

Answer

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.

Question 5

What does a 'misfire detected on cylinder 3' (P0303) DTC indicate a technician should check FIRST?

Accepted Answer

Spark plug, ignition coil, and fuel injector on cylinder 3

Answer

A cylinder-specific misfire code directs the technician to inspect components directly responsible for combustion in that cylinder: spark plug, coil, and injector.

(MTC) Marine Technician Certification Practice Test

(MTC) Marine Technician Certification Practice Test

MTC Engine Performance & Tuning 5