ASE A8 Engine Performance Practice Test

11. Which of the following is LEAST likely to result in a rich air fuel ratio?

  • A. A leaking fuel injector.
  • B. A faulty fuel pressure regulator.
  • C. A faulty ECT engine coolant temperature sensor.
  • D. A stuck closed thermostat.

11.

Answer A is wrong. A leaking fuel injector will cause a rich air fuel ratio.

Answer B is wrong. A faulty fuel pressure regulator will cause a rich air fuel ratio.

Answer C is wrong. A faulty ECT will cause a rich air fuel ratio.

Answer D is correct. A stuck closed thermostat will cause a vehicle to overheat. A thermostat that's stuck open delays or prevents the engine from reaching its optimum operating temperature resulting in a rich air fuel ratio.

12. Two technicians are discussing a four wire oxygen sensor. Technician A says this oxygen sensor contains a heater circuit. Technician B says the engine's control module uses the oxygen sensor's voltage signal to adjust the air fuel ratio in closed loop. Who is correct?

  • A. Technician A
  • B. Technician B
  • C. Both A and B
  • D. Neither A or B

12.

Answer A is wrong. Both technicians are correct. The oxygen sensor contains a heater to bring it to operating temperature sooner.

Answer B is wrong. Both technicians are correct.

Answer C is correct. An oxygen sensor's heater circuit is designed to bring the system to closed loop quickly. It sends a voltage signal to the engine control module in relation to the oxygen content of the exhaust stream.

Answer D is wrong. Both technicians are correct.

Diagram of automotive PCM engine control system.

13. Component A in the diagram above is:

  • A. Part of the primary ignition system.
  • B. Switched by the secondary circuit.
  • C. Part of the secondary ignition system
  • D. Both A and C.

13.

Answer A is wrong. Both A and C are correct. An ignition coil is part of the primary and the secondary circuits.

Answer B is wrong. An ignition coil is controlled or switched by the primary circuit.

Answer C is wrong. It is part of both circuits.

Answer D is correct. Both Technicians A and C are correct.

14. An emissions test is performed on a six cylinder engine. The test indicates high levels of NOx. The MOST likely cause of this condition is:

  • A. A rich air fuel mixture.
  • B. A clogged catalytic converter.
  • C. A cylinder misfire.
  • D. A stuck closed EGR valve.

14.

Answer A is wrong. A rich fuel mixture will increase HC or hydrocarbon emissions.

Answer B is wrong. A clogged catalytic converter will result in a loss of power.

Answer C is wrong. A cylinder misfire will result in excessive HC's due to the increase of unburned fuel.

Answer D is correct. A stuck closed EGR valve will result in high cylinder temperatures. This excessive heat results in high levels of NOx in the emissions.

15. A technician is using a digital multimeter to test a ground circuit for excessive resistance. Technician A says to perform a voltage drop test on this circuit. Technician B says an ohmmeter is used and voltage must be present while performing this resistance test. Who is correct?

  • A. Technician A
  • B. Technician B
  • C. Both A and B
  • D. Neither A or B

15.

Answer A is correct. A voltage drop test would verify a poor or corroded ground circuit or connection.

Answer B is wrong. A voltage drop test is a great way to find resistance in a circuit. Never use an ohmmeter when voltage is present in a circuit though. Doing so can damage the meter.

Answer C is correct. Technician A is correct.

Answer D is wrong. Perform a voltage test to find excessive resistance in a circuit.