ASE A8 Engine Performance Practice Test
16. The PCV valve has been removed from an engine's valve cover and makes a rattling sound when shaken. Which of the following statements is correct?
- A. The PCV valve is clogged.
- B. The PCV valve's spring is broken.
- C. The PCV valve is stuck open.
- D. This is normal.
Answer A is wrong. A clogged or stuck closed PCV valve results in excessive crankcase pressure and oil leaking past oil seals and gaskets.
Answer B is wrong. A PCV valve uses light spring pressure to hold the valve in the open position while the engine isn't running or when there's a drop in manifold vacuum, like during acceleration.
Answer C is wrong. A stuck open PCV valve or leaking PCV hose results in a lean air-fuel ratio and drivability issues like surging.
Answer D is correct. When removed from the engine, the PCV valve should rattle when shaken. Please note that if the valve does not rattle, it's clogged and must be replaced.
17. An engine with an electronic ignition system has no spark at any of the ignition coils. Which of the following is MOST likely causing this no-start condition?
- A. A clogged air filter.
- B. A faulty fuel pump.
- C. A faulty crankshaft position sensor.
- D. A faulty EGR valve.
Answer A is wrong. A clogged air filter restricts airflow to the engine, resulting in a rich air-fuel ratio.
Answer B is wrong. A faulty fuel pump results in low or no fuel pressure at the fuel rail.
Answer C is correct. The symptoms of a faulty crankshaft position sensor include no-start, intermittent start, and poor engine performance. This sensor affects fuel and ignition timing.
Answer D is wrong. A stuck open Exhaust Gas Recirculation valve results in a lean air-fuel mixture. A stuck closed EGR valve results in high cylinder temperatures, pre-ignition, ping, and knock.
18. A vehicle has a check engine light with codes indicating a problem with the enhanced evaporative emission system. It has a rough idle and difficulty starting. Which of the following will result in this condition?
- A. A clogged charcoal canister.
- B. A faulty purge solenoid.
- C. A faulty fuel level sensor.
- D. An open vent valve.
Answer A is wrong. The canister contains a charcoal insert that absorbs and retains fuel vapor until it's purged into the intake manifold for combustion.
Answer B is correct. The purge solenoid/valve is responsible for venting the tank's fuel vapor into the intake manifold. A faulty purge solenoid results in a rough idle, and difficulty starting.
Answer C is wrong. A faulty fuel level sensor leads to false readings at the fuel gauge.
Answer D is wrong. The vent allows fresh air to enter the canister. The valve is also used by the PCM to monitor purge valve operation.
19. The #1 cylinder is disabled on a four-cylinder engine. There is a slight drop in RPM. Technician A says the engine should stumble when the cylinder is disabled. Technician B says there should be a significant drop in RPM during this test. Who is correct?
- A. Technician A
- B. Technician B
- C. Both A and B
- D. Neither A or B
Answer A is wrong. A significant drop in rpm should be noticed when the cylinder is disabled.
Answer B is wrong. Notice the drop as the cylinder is disabled. If a cylinder's drop is not consistent with the others, this indicates a problem with that cylinder.
Answer C is correct. This is not considered normal, especially with a four-cylinder engine. The engine should begin to stumble and lose its balance from the loss of the cylinder's power contribution.
Answer D is wrong. An engine cylinder power balance test indicates the power of each cylinder, testing its effectiveness compared to the others.
20. The test results above were recorded during a cylinder compression test. Which of the following is MOST likely causing these test results?
- A. A faulty head gasket.
- B. Weak piston rings.
- C. Burned exhaust valves.
- D. Incorrect valve timing.
Answer A is correct. When there are low compression pressures in adjacent cylinders the head gasket is leaking compression between the two or there is a crack in the deck or cylinder head. It is usually the head gasket.
Answer B is wrong. A technician will know if it has faulty piston rings if the compression increases after injecting oil.
Answer C is wrong. To check for a burned exhaust valve inject some oil in the cylinder and test again. If the pressure increases it's because the oil has improved the seal between the piston rings and the cylinder. If it doesn't increase a valve is most likely the problem.
Answer D is wrong. Improper valve timing would not result in this condition. It would affect more cylinders.