MTC Engine Performance & Tuning 4

Question 1

When diagnosing a marine engine with an oxygen sensor, a consistently high voltage (0.8-0.9V) output indicates:

Accepted Answer

A rich exhaust condition

Answer

A lean exhaust condition

Answer

Normal stoichiometric mixture

Answer

A failed oxygen sensor

Question 2

What does a technician check when performing a throttle position sensor (TPS) calibration on a marine EFI engine?

Accepted Answer

That the TPS reads 0% at idle and 100% at WOT with correct voltage range

Answer

That idle speed is within specification

Answer

That the fuel pressure matches spec at WOT

Answer

That ignition timing advances with throttle position

Question 3

A marine engine misfires only at high RPM under load. Ignition components test normal. Which fuel system issue should be suspected?

Accepted Answer

Weak fuel pump unable to maintain pressure under high demand

Answer

Clogged fuel return line

Answer

Stuck-open fuel pressure regulator

Answer

Leaking fuel injector at idle

Question 4

On a marine diesel engine, what is the purpose of the injection advance mechanism?

Accepted Answer

Advance injection timing as engine speed increases for optimum combustion

Answer

Increase fuel delivery volume at high RPM

Answer

Retard timing to prevent overheating

Answer

Control smoke output under load

Question 5

A marine engine cooling system pressure test shows a 5 psi drop over 10 minutes. This indicates:

Accepted Answer

An internal or external coolant leak

Answer

Normal heat expansion

Answer

Thermostat is stuck open

Answer

Water pump is failing

Question 6

When measuring piston ring end gap during engine overhaul, what is the consequence of installing rings with insufficient end gap?

Accepted Answer

Ring ends butt together as rings expand from heat, causing ring breakage or scuffing

Answer

Excessive blow-by past the rings

Answer

Increased oil consumption

Answer

Poor cylinder sealing at operating temperature

Question 7

Which parameter does a knock sensor monitor to allow the ECM to protect a marine engine?

Accepted Answer

Crankshaft vibration frequencies associated with detonation

Answer

Combustion chamber temperature

Answer

Intake manifold pressure changes

Answer

Exhaust backpressure