ASE A8 Engine Performance Practice Test

1. After performing a wet compression test, the pressure in each of the cylinders increased, but remained below specifications. Technician A says this is caused by incorrect valve timing. Technician B says this is caused by worn piston rings. Who is correct?

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

1.

Answer A is wrong. It is true that incorrect valve timing results in low compression readings in all of the engine's cylinders, but the pressures increased because of the engine oil introduced into the cylinder. It increased the seal between the piston rings and the engine's cylinder walls. This engine most likely has worn piston rings.

Answer B is correct. If the engine has worn piston rings, the pressure readings increase after injecting oil.

Answer C is wrong. Technician B is correct.

Answer D is wrong. Technician B is correct.

2. A vacuum gauge is connected to a port on the intake manifold of an engine with poor performance. The needle on the gauge fluctuates between 15 "hg and 20 "hg vacuum at idle. This vacuum gauge reading indicates:

  • A. A normal condition.
  • B. Late ignition or valve timing.
  • C. A burned exhaust valve.
  • D. A restricted exhaust.

2.

Answer A is wrong. A gauge that reads steady (17 "hg - 21 "hg) indicates a normal running engine. Vacuum is measured inches of mercury vacuum or "hg.

Answer B is wrong. A gauge that reads a steady low (15 "hg - 20 "hg) indicates late valve or ignition timing, leaking manifold gasket, low compression, leaking carburetor or a stuck throttle valve.

Answer C is correct. A gauge that fluctuates between (15 "hg and 20 "hg) indicates a stuck valve or an engine misfire.

Answer D is wrong. A gauge needle that drops slowly at idle indicates a clogged or blocked exhaust.

3. Technician A says a stuck closed (EGR) exhaust gas recirculating valve will cause an engine to stumble or stall. Technician B says a stuck open EGR valve will cause detonation. Who is correct?

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

3.

Answer A is wrong. A stuck open, not closed EGR valve will cause an engine to stumble or stall.

Answer B is wrong. A stuck closed, not open EGR valve will cause harmful engine detonation.

Answer C is wrong. Neither technician is correct.

Answer D is correct. Neither technician is correct.

4. A vehicle is emitting black smoke from its tailpipe at idle. Which of the following is causing this condition?

  • A. A leaking fuel injector.
  • B. Worn piston rings.
  • C. A blown head gasket.
  • D. Leaking valve seals.

4.

Answer A is correct. A leaking fuel injector causes a rich fuel mixture. A rich fuel condition causes black colored exhaust. (Fuel)

Answer B is wrong. Worn rings cause blue gray colored exhaust. (Oil)

Answer C is wrong. A blown head gasket causes white gray exhaust. (Coolant)

Answer D is wrong. Leaking valve seals produce blue gray exhaust. (Oil)

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.