LEC Engine Performance & Diagnostics 2 — Questions and Answers
Question 1: A locomotive's turbocharger is surging at low throttle settings. What is the most likely cause?
- Excessive fuel injection timing advance
- Compressor wheel contamination or worn bearings (Correct answer)
- High ambient temperature reducing air density
- Overfilled engine oil crankcase
Correct answer: Compressor wheel contamination or worn bearings
Turbocharger surging at low throttle is typically caused by compressor wheel contamination, fouling, or worn bearings that disrupt proper airflow.
Question 2: When performing a cylinder cutout test, what indicates a cylinder is contributing normally to engine output?
- Engine RPM increases when the cylinder is cut out
- Engine RPM drops noticeably when the cylinder is cut out (Correct answer)
- Exhaust temperature rises on adjacent cylinders
- Fuel rack position remains unchanged
Correct answer: Engine RPM drops noticeably when the cylinder is cut out
A significant RPM drop when a cylinder is cut out confirms that cylinder was producing power; no drop indicates a non-contributing cylinder.
Question 3: A locomotive engineer notices black smoke from the exhaust at full throttle. Which condition is LEAST likely to cause this?
- Restricted air filter reducing combustion air
- Faulty injector delivering excess fuel
- Turbocharger compressor damage reducing boost
- Engine oil diluted with coolant (Correct answer)
Correct answer: Engine oil diluted with coolant
Coolant-diluted oil typically causes white or blue smoke, not black smoke; black smoke indicates incomplete combustion from excess fuel or insufficient air.
Question 4: What does a consistently high exhaust back pressure reading indicate on a diesel locomotive?
- The turbocharger is producing excessive boost
- The exhaust system is partially blocked or restricted (Correct answer)
- Fuel injection timing is too early
- Cooling water temperature is above normal
Correct answer: The exhaust system is partially blocked or restricted
High exhaust back pressure signals a restriction in the exhaust path, such as a clogged muffler, damaged piping, or collapsed exhaust components.
Question 5: During engine startup, a locomotive shows excessive oil consumption with blue exhaust smoke. The most probable cause is:
- Worn piston rings or valve seals allowing oil into combustion chamber (Correct answer)
- Insufficient fuel delivery to injectors
- Cracked fuel injector tip leaking diesel
- Clogged air filter reducing combustion efficiency
Correct answer: Worn piston rings or valve seals allowing oil into combustion chamber
Blue smoke indicates burning engine oil, most commonly caused by worn piston rings or valve stem seals that allow oil to enter the combustion chamber.
Question 6: A locomotive's load meter reads higher than expected for a given throttle notch while horsepower output is normal. This suggests:
- The engine is operating at reduced efficiency requiring more current for same output (Correct answer)
- The traction motors are disconnected from the trucks
- The fuel injectors are delivering insufficient fuel
- The main generator field current is too low
Correct answer: The engine is operating at reduced efficiency requiring more current for same output
Higher-than-expected amperage for normal horsepower output indicates reduced efficiency in the power conversion chain, often from traction motor or generator issues.
Question 7: Which diagnostic parameter BEST indicates intercooler effectiveness on a turbocharged diesel locomotive?
- Difference between turbocharger outlet temperature and intake manifold temperature (Correct answer)
- Difference between exhaust temperature and ambient temperature
- Fuel rack position at idle
- Coolant temperature differential across the radiator
Correct answer: Difference between turbocharger outlet temperature and intake manifold temperature
Intercooler effectiveness is measured by how much the turbocharger outlet air temperature drops before reaching the intake manifold.
LEC Engine Performance & Diagnostics 2
A locomotive's turbocharger is surging at low throttle settings.
What is the most likely cause?