LEC Engine Performance & Diagnostics 3 — Questions and Answers
Question 1: A diesel locomotive engine experiences a sudden drop in oil pressure while operating at Notch 8. The engineer should FIRST:
- Reduce throttle to Notch 4 and continue to the next siding
- Immediately place throttle to idle and prepare to shut down (Correct answer)
- Increase throttle to maintain speed and monitor the gauge
- Switch to backup oil pump if equipped and continue
Correct answer: Immediately place throttle to idle and prepare to shut down
A sudden oil pressure drop is a critical emergency requiring immediate throttle reduction to idle and engine shutdown preparation to prevent severe engine damage.
Question 2: What is the purpose of the load regulator on an EMD diesel-electric locomotive?
- To regulate cooling fan speed based on engine temperature
- To maintain constant engine RPM by adjusting generator excitation load (Correct answer)
- To control fuel injection timing across all throttle notches
- To balance current between parallel traction motors
Correct answer: To maintain constant engine RPM by adjusting generator excitation load
The load regulator controls generator excitation to match electrical load to engine capability, keeping engine RPM constant at each throttle notch.
Question 3: Which of the following best describes 'dynamic braking capacity' limits related to engine diagnostics?
- Dynamic braking is limited by maximum safe exhaust temperature
- Dynamic braking capacity is limited by traction motor cooling capacity and grid resistor temperature (Correct answer)
- Dynamic braking output is limited by fuel delivery rate to the engine
- Dynamic braking is limited by maximum generator field current
Correct answer: Dynamic braking capacity is limited by traction motor cooling capacity and grid resistor temperature
Dynamic braking capacity is thermally limited by the ability of grid resistors and traction motors to dissipate the heat generated during braking.
Question 4: An engine overspeed trip activates during a downhill grade with dynamic brakes applied. What is the most likely cause?
- The dynamic brake grids have failed open, removing the load from the engine (Correct answer)
- Excessive fuel delivery from a stuck injector
- Cooling system failure causing thermal runaway
- High altitude reducing air density and combustion efficiency
Correct answer: The dynamic brake grids have failed open, removing the load from the engine
If dynamic brake grids fail open, the generator load is removed from the engine, which can accelerate to overspeed if throttle is not immediately reduced.
Question 5: Water in the fuel system of a diesel locomotive most commonly results in:
- Increased horsepower output due to steam injection effect
- Injector tip corrosion, rough running, and potential injector failure (Correct answer)
- Lower exhaust temperatures indicating cleaner combustion
- Reduced turbocharger boost pressure
Correct answer: Injector tip corrosion, rough running, and potential injector failure
Water in diesel fuel causes injector corrosion, poor atomization, rough combustion, and can lead to catastrophic injector failure.
Question 6: A locomotive's engine will not transition from idle to Notch 1 when the throttle is advanced. Which system should be checked first?
- Fuel injector calibration on all cylinders
- Engine throttle control circuit, governor, and throttle response wiring (Correct answer)
- Traction motor brush condition and commutator
- Exhaust back pressure sensor calibration
Correct answer: Engine throttle control circuit, governor, and throttle response wiring
Failure to respond to throttle advancement points to the control circuit, governor, or wiring between the throttle handle and engine speed control system.
Question 7: Crankcase pressure that exceeds normal limits on a diesel locomotive indicates:
- Excessive combustion gas blowby past worn piston rings (Correct answer)
- Normal high-load operation at Notch 8
- Turbocharger compressor surge condition
- Fuel rack at maximum travel position
Correct answer: Excessive combustion gas blowby past worn piston rings
Excessive crankcase pressure is caused by combustion gases blowing past worn piston rings into the crankcase, a condition called blowby.
LEC Engine Performance & Diagnostics 3
A diesel locomotive engine experiences a sudden drop in oil pressure while operating at Notch 8.
The engineer should FIRST: