310T Engine and Fuel Systems 4 — Questions and Answers
Question 1: Which diesel engine emission control system recirculates exhaust gases back into the intake to reduce NOx emissions?
- Diesel Particulate Filter (DPF)
- Selective Catalytic Reduction (SCR)
- Exhaust Gas Recirculation (EGR) (Correct answer)
- Diesel Oxidation Catalyst (DOC)
Correct answer: Exhaust Gas Recirculation (EGR)
EGR reduces peak combustion temperatures by diluting the intake charge with inert exhaust gas, which lowers the formation of NOx.
Question 2: During a diesel injector balance rate test, one injector shows a significantly higher fuel delivery than the others. This indicates the injector is:
- Delivering too little fuel and needs replacement
- Delivering too much fuel, possibly stuck open or leaking (Correct answer)
- Operating normally at higher load
- Receiving too much rail pressure
Correct answer: Delivering too much fuel, possibly stuck open or leaking
A high balance rate means the ECM is commanding more fuel to compensate, indicating the injector is delivering too little—not too much—fuel on its own.
Question 3: What causes diesel engine 'cavitation erosion' damage to cylinder liners?
- Abrasive particles in the engine oil
- Coolant pressure fluctuations causing vapor bubble collapse on the liner exterior (Correct answer)
- High fuel sulfur content attacking the liner surface
- Improper piston ring gap causing liner scuffing
Correct answer: Coolant pressure fluctuations causing vapor bubble collapse on the liner exterior
Cavitation erosion occurs when coolant pressure waves cause vapor bubbles to form and implode against the wet cylinder liner's outer surface.
Question 4: A technician is diagnosing a no-start condition on a diesel. Fuel pressure is correct but the engine will not start. What should be checked next?
- Engine oil level
- Glow plug or grid heater operation (Correct answer)
- Alternator output voltage
- Power steering fluid level
Correct answer: Glow plug or grid heater operation
If fuel pressure is adequate and the engine won't start in cold or normal conditions, faulty glow plugs or a grid heater are a primary suspect for diesels.
Question 5: What is the function of the intake throttle valve (ITV) on a modern diesel engine equipped with EGR?
- Controls engine speed at idle
- Creates intake manifold vacuum to draw EGR gases into the intake (Correct answer)
- Limits maximum airflow to reduce engine noise
- Prevents engine overspeed during downhill operation
Correct answer: Creates intake manifold vacuum to draw EGR gases into the intake
The intake throttle valve partially restricts airflow to create a pressure differential that helps pull EGR gases into the intake manifold.
Question 6: When should diesel engine valve lash (valve clearance) be adjusted?
- Only when the engine is at normal operating temperature
- Only when the engine is cold and at TDC for each cylinder (Correct answer)
- Only on engines with more than 100,000 miles
- At any temperature, as it does not affect the measurement
Correct answer: Only when the engine is cold and at TDC for each cylinder
Valve lash must be set with the engine cold and the piston at TDC compression stroke to ensure accurate clearance per manufacturer specification.
Question 7: A diesel engine's oil analysis report shows a high silicon content. What does this most likely indicate?
- Oil additive breakdown
- Air filter failure allowing dirt ingestion (Correct answer)
- Coolant contamination from a head gasket
- Excessive fuel dilution of engine oil
Correct answer: Air filter failure allowing dirt ingestion
Silicon is the primary indicator of dirt contamination, most often caused by a compromised air filtration system allowing abrasive particles into the engine.
310T Engine and Fuel Systems 4
Which diesel engine emission control system recirculates exhaust gases back into the intake to reduce NOx emissions?