EETC - Equipment & Engine Training Council Compact Diesel Engine Repair Questions and Answers — Questions and Answers
Question 1: A compact diesel engine is difficult to start, especially in cold weather, and produces excessive white smoke upon starting. Which of the following is the MOST likely cause?
- Clogged fuel filter
- Malfunctioning glow plugs (Correct answer)
- Low engine compression
- A faulty starter motor
Correct answer: Malfunctioning glow plugs
Faulty glow plugs are a primary cause of hard starting in cold weather for diesel engines. Glow plugs are heating elements that warm the combustion chamber to aid in ignition. When they fail, the engine struggles to reach the temperature needed for combustion, resulting in hard starting and white smoke (unburnt fuel).
Question 2: When testing a common rail fuel injector, a technician performs a return flow (back-leak) test. What is the primary purpose of this test?
- To measure the volume of fuel delivered to the cylinder.
- To check for external fuel leaks around the injector body.
- To verify the electrical resistance of the injector solenoid.
- To identify excessive internal leakage within the injector. (Correct answer)
Correct answer: To identify excessive internal leakage within the injector.
The return flow, or back-leak, test measures the amount of fuel that bypasses the nozzle and returns to the tank. Excessive return flow indicates internal wear or damage, such as a worn valve seat, which prevents the injector from holding proper pressure for efficient atomization.
Question 3: The primary function of a turbocharger's wastegate on a compact diesel engine is to:
- Increase exhaust gas temperature for DPF regeneration.
- Cool the compressed intake air before it enters the engine.
- Limit the maximum boost pressure to protect the engine. (Correct answer)
- Reduce engine noise during high RPM operation.
Correct answer: Limit the maximum boost pressure to protect the engine.
A wastegate is a valve that diverts a portion of the exhaust gas flow around the turbine wheel of the turbocharger. This action limits the turbine's speed, which in turn regulates the speed of the compressor and controls the maximum boost pressure, preventing engine damage from over-boosting.
Question 4: A technician is servicing a compact diesel engine equipped with a Diesel Particulate Filter (DPF). The operator reports frequent DPF warning lights and poor performance, primarily during low-speed, stop-and-go operation. What is the most likely reason for these symptoms?
- The engine oil is of the wrong viscosity.
- Failure of the passive regeneration process. (Correct answer)
- A cracked exhaust manifold.
- The fuel's cetane rating is too high.
Correct answer: Failure of the passive regeneration process.
Passive regeneration requires high exhaust temperatures, typically achieved during highway driving or high-load conditions, to burn off soot. In low-speed, stop-and-go operation, the exhaust temperature is often too low for passive regeneration to occur effectively, leading to soot accumulation and the triggering of active or forced regeneration cycles and warning lights.
Question 5: When using a multimeter to test the resistance of a glow plug, what would a reading of 'OL' (Over Limit) or infinity most likely indicate?
- A short circuit to ground.
- The glow plug is functioning correctly.
- An open circuit within the glow plug element. (Correct answer)
- The engine block is not properly grounded.
Correct answer: An open circuit within the glow plug element.
A reading of 'OL' or infinity on a multimeter set to measure resistance (Ohms) indicates an open circuit. In the context of a glow plug, this means the internal heating element is broken and cannot complete the electrical circuit, rendering it inoperative.
Question 6: Which of the following is a critical first step when diagnosing a 'crank, no start' condition on a modern compact diesel engine?
- Immediately performing an engine compression test.
- Checking for diagnostic trouble codes (DTCs) with a scan tool. (Correct answer)
- Replacing the fuel filter and bleeding the system.
- Testing the output of the starter motor.
Correct answer: Checking for diagnostic trouble codes (DTCs) with a scan tool.
Modern diesel engines are heavily controlled by an Engine Control Module (ECM). Scanning for DTCs should be the first step, as a fault code can quickly direct the technician to the specific system (e.g., fuel pressure, sensor input, glow plug circuit) that is preventing the engine from starting, saving significant diagnostic time.
EETC - Equipment & Engine Training Council Compact Diesel Engine Repair Questions and Answers
A compact diesel engine is difficult to start, especially in cold weather, and produces excessive white smoke upon starting.
Which of the following is the MOST likely cause?