ASE A8 Engine Performance Practice Test

1. Technician A says the PCM will advance the engine's ignition timing when it receives a voltage signal from the knock sensor. Technician B says this sensor sends an AC signal to the PCM when it detects ping or detonation. Who is correct?

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

1.

Answer A is wrong. The PCM retards the engine's ignition timing when it receives a voltage signal from the knock sensor. Retarding the engine's ignition timing helps prevent detonation (knock).

Answer B is correct. The knock sensor creates and sends an AC voltage signal to the PCM whenever it senses vibration from engine knock or ping.

Answer C is wrong. Technician B is correct.

Answer D is wrong. Technician B is correct.

2. A vehicle has a momentary hesitation only during acceleration. The MOST likely cause of this condition is:

  • A. A faulty exhaust gas recirculating valve. (EGR)
  • B. A faulty oxygen sensor. (O2) sensor
  • C. A faulty positive crankcase ventilation valve. (PCV)
  • D. A faulty throttle position sensor. (TPI)

2.

Answer A is wrong. This actuator would not likely cause this condition.

Answer B is wrong. This sensor would not likely cause this condition.

Answer C is wrong. This valve would not likely cause this condition.

Answer D is correct. A faulty TP sensor would cause this condition.

3. A four cylinder EFI engine has an engine code indicating insufficient EGR flow. The EGR solenoid has been tested and found to be faulty. This faulty solenoid will result in which of these conditions.

  • A. High CO emissions.
  • B. High HC emissions.
  • C. High CO2 emissions.
  • D. High NOx emissions.

3.

Answer A is wrong. CO stands for carbon monoxide. Carbon monoxide is the toxic compound that forms with partially burned fuel from rich fuel mixtures.

Answer B is wrong. HC stands for hydrocarbon. Hydrocarbons are unburned fuel resulting from rich fuel mixtures and misfires.

Answer C is wrong. CO2 stands for carbon dioxide. Carbon dioxide is actually desired over carbon monoxide, though it is considered a greenhouse gas.

Answer D is correct. NOx stands for oxides of nitrogen. The x is a variable. These gases are formed with high cylinder temperatures. They are considered pollutants. A stuck open EGR valve will result in excessive exhaust gas flow into the intake manifold. This results in engine stumble at idle. A stuck closed EGR valve will result in excessive NOx emissions.

4. Technician A says an AF (Air/Fuel) sensor is designed to reach and keep an engine at stoichiometry. Technician B says stoichiometry is 15.7:1 air to fuel mixture. Who is correct?

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

4.

Answer A is correct. An Air/Fuel sensor is designed to reach and keep a vehicle at stoichiometry.

Answer B is wrong. Stoichiometry is a (14.7:1) air to fuel mixture. This is an important ratio to remember.

Answer C is wrong. Technician A is correct.

Answer D is wrong. Technician A is correct.

5. A vehicle with an enhanced EVAP system is scanned and a code indicating a small evaporative emissions leak is detected. A loose or cracked gas cap is suspected. Technician A says the cap contains a vacuum and pressure relief valve, a small crack in the cap will not illuminate the check engine light. Technician B says the tank contains a sensor. The PCM will sense low tank pressure, set a code and illuminate the check engine light. Who is correct?

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

5.

Answer A is wrong. A crack in the cap will alter system pressure. The gas caps contain these valves, but are calibrated by the manufacturer to maintain a certain pressure in the tank. Check for a loose cap, if the cap is cracked it should be replaced with a cap that matches the manufacturer's specifications.

Answer B is correct. Today's enhanced EVAP systems use a fuel tank pressure sensor that measures pressure at the tank. They will set a code and illuminate the check engine light if a faulty or damaged gas cap is found of left loose. Some systems contain pumps and operate the purge and vent valves; they run system tests, sometimes hours after shutdown, checking for small or large leaks in the system.

Answer C is wrong. Technician B is correct.

Answer D is wrong. Technician B is correct.