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ASE Automobile

A9 Light-Vehicle Diesel Engines — practice test

Studying for A9 (Light-Vehicle Diesel Engines)? Overhaul Prep has 121 verified A9 questions written to the current task list — in the same formats the real exam uses (direct, Technician A/B, EXCEPT and most-likely-cause). Every answer comes with a written explanation, so you learn why instead of memorising a letter.

121A9 questions
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9,711questions in total
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Sample A9 questions

Straight from the bank — answers highlighted, with the explanation underneath.

In a light-duty high-pressure common-rail (HPCR) diesel fuel system, which component is responsible for generating the extreme injection pressures (roughly 20,000-30,000 psi) stored in the rail?

  1. The fuel transfer (lift) pump
  2. The high-pressure fuel pump
  3. The rail pressure sensor
  4. The injector solenoid or piezo actuator
WhyThe engine-driven high-pressure pump develops the rail pressure; the transfer/lift pump only supplies low-pressure fuel to feed it, the rail sensor merely reports pressure, and the injectors meter already-pressurized fuel rather than creating the pressure.

Two technicians discuss diesel compression test results. Technician A says the readings between cylinders should be reasonably even, and excessive variation (commonly more than about 10-15%) indicates a problem. Technician B says a healthy light-duty diesel typically produces only about 120-150 psi cranking compression, similar to a gasoline engine. Who is correct?

  1. Technician A only
  2. Technician B only
  3. Both Technicians A and B
  4. Neither Technician
WhyA is correct — cylinders should stay within roughly 10-15% of each other. B is wrong: light-duty diesels crank far higher than gasoline engines, commonly in the 400-500 psi range or more.

All of the following are true of a diesel exhaust gas recirculation (EGR) system EXCEPT:

  1. It recirculates inert exhaust gas into the intake charge
  2. It lowers peak combustion temperature
  3. It reduces oxides of nitrogen (NOx) formation
  4. It reduces diesel particulate (soot) formation
WhyEGR routes inert exhaust back into the intake to lower peak combustion temperature, which suppresses NOx formation. However, it does not reduce soot-by lowering temperature and oxygen it tends to increase particulate matter, which is why DPFs and EGR must be balanced.

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