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

Connected and engine at operating temperature

Answer

Connected at idle with all accessories on

Answer

Disconnected only at wide-open throttle

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

Engine runs cooler, improving performance

Answer

Cooling system pressure increases significantly

Answer

Fuel mixture becomes leaner

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

Rich mixture or oil fouling

Answer

Cold fouling from short trips

Answer

Normal wear on a high-mileage engine

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

Fuel injector leaking-down overnight

Answer

Overfilled crankcase oil level

Answer

Clogged air filter restricting airflow

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

Fuel pressure regulator

Answer

Crankshaft position sensor

Answer

Throttle position sensor

Question 6

On a marine EFI engine, the long-term fuel trim (LTFT) reads +22%. What does this indicate?

Accepted Answer

The engine is running lean and the ECM is adding fuel to compensate

Answer

The engine is running rich and the ECM is adding fuel

Answer

Fuel injectors are delivering too much fuel

Answer

The oxygen sensor has failed rich

Question 7

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?

Accepted Answer

Worn or broken piston rings in that cylinder

Answer

Burnt exhaust valve in that cylinder

Answer

Blown head gasket between cylinders

Answer

Cracked piston in that cylinder