ASE A8 Engine Performance Practice Test

46. An engine with a vacuum-operated EGR valve has fault code P0401 indicating insufficient EGR flow. The engine stumbles, and there is a significant drop in RPM when the EGR diaphragm is activated using a portable vacuum pump. Which of the following is causing this condition?

  • A. A faulty EGR position sensor.
  • B. A faulty EGR valve.
  • C. A clogged EGR passage.
  • D. A faulty EGR vacuum solenoid.

46.

Answer A is wrong. The EGR position sensor informs the ECM of the EGR valve's position.

Answer B is wrong. The inert gas from the EGR valve prevents the cylinders from reaching high temperatures, inhibiting the formation of smog-forming NOx.

Answer C is wrong. Before replacing an exhaust gas recirculation valve, inspect the passage in the intake manifold. A restriction in the passage results in insufficient flow. If it's clogged, use a small wire brush to remove the carbon.

Answer D is correct. When a manual vacuum pump activates the EGR valve, it bypasses the solenoid, the electrical/vacuum circuits, and the ECM. The engine's stumbling and a notable drop in RPM eliminate the EGR valve and the passages as the problem.

47. A cylinder power balance test indicates two adjacent cylinders are underperforming. All of the following would cause this result EXCEPT:

  • A. Crossed ignition wires.
  • B. A leaking head gasket.
  • C. A faulty COP ignition coil.
  • D. A cracked cylinder head.

47.

Answer A is wrong. Clips keep the ignition wiring separated and help prevent leaking insulation and crossfire.

Answer B is wrong. A faulty head gasket leaking between two adjacent cylinders will affect both cylinders.

Answer C is correct. A (COP) coil on plug ignition system has a coil mounted directly over the spark plug of each cylinder. A faulty coil results in a misfire at that particular cylinder.

Answer D is wrong. A cracked cylinder head or block will cause a leak between cylinders.

48. An engine with a (COP) coil on plug ignition system cranks but will not start. A voltage meter measures 0.00 volts at each of the coil's (B+) power feeds. Which of the following is MOST likely causing this no start condition?

  • A. An open in the primary circuit.
  • B. The ECM's driver is faulty.
  • C. Resistance in the secondary circuit.
  • D. A faulty Engine Control Module.

48.

Answer A is wrong. An open in the primary circuit will affect only one ignition coil.

Answer B is wrong. A faulty (ECM) Engine Control Module driver will cause no spark at only one of the coils.

Answer C is wrong. Resistance in the secondary circuit will affect only one of the coils. With (COP) or coil on plug ignition systems, a coil is placed over each spark plug eliminating the need for spark plug wires.

Answer D is correct. A loss of power from a defective ECM relay or fuse or a faulty ECM will result in no power to any of the coils and a no spark condition. This problem will also affect the fuel injectors. An (EI) electronic ignition system uses a (CKP) crankshaft position sensor. A faulty CKP sensor will also result in a no spark condition.

49. A Heated-wire Mass Air Flow sensor has deposits coating its tip, affecting its signal to the engine control module. Technician A says this results in a loss of power and hesitation. Technician B says these deposits affect the air-fuel ratio. Who is correct?

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

49.

Answer A is wrong. Utilize the OBDII fuel trim monitor. A dirty or faulty (MAF) Mass Air Flow sensor affects fuel trim resulting in a loss of power, hesitation, and reduced fuel mileage.

Answer B is wrong. The (MAF) Mass Air Flow Sensor senses airflow volume in the air tube. It provides the ECM and TCM with valuable information regarding engine load.

Answer C is correct. Both technicians are correct. The coating results in a slightly rich air-fuel ratio at idle and low speeds.

Answer D is wrong. Because the heated filament gets dirty from time and wear, a filament cleaning can sometimes return the MAF's function.

50. Technician A says a (TPI) throttle position sensor is a potentiometer that indicates throttle angle. Technician B says a throttle position sensor can be tested for resistance with an ohmmeter. Who is correct?

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

50.

Answer A is wrong. The TPI, TPS or throttle position sensor is a potentiometer that varies voltage signals to the PCM according to throttle angle. Both technicians are correct.

Answer B is wrong. This sensor is best tested with a scanner but can be tested for proper resistance and sweep with an ohmmeter.

Answer C is correct. Both technicians are correct.

Answer D is wrong. Both technicians are correct.

ASE A8 Engine Performance Quiz
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