ASE A8 Engine Performance Practice Test

6. Two technicians are discussing turbocharger boost pressure. Technician A says a boost pressure sensor provides the intake manifold's boost pressure to the PCM. Technician B says a leaking wastegate diaphragm will effect exhaust flow through the turbine wheel. Who is correct?

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

6.

Answer A is wrong. Both technicians are correct. The boost pressure sensor provides the intake manifold's boost pressure to the PCM and is typically located on the charger. A turbocharger improves the volumetric efficiency of an engine. A turbocharger creates positive pressure in the intake manifold. A 5 psi boost adds an additional 5 psi to atmospheric pressure (14.7 psi) creating 19.7 psi.

Answer B is wrong. A spring keeps this gate normally closed at idle. As pressure increases, the valve opens the wastegate allowing exhaust pressure to bypass the turbine wheel.

Answer C is correct. Both technicians are correct.

Answer D is wrong. Both technicians are correct.

Diagram of automotive PCM engine control system.

7. The vehicle in the diagram above contains:

  • A. A (COP) coil on plug ignition system.
  • B. A wastespark ignition system.
  • C. A sequential port electronic fuel injection system.
  • D. A (TBI) throttle body fuel injection system.

7.

Answer A is wrong. This is a wastespark ignition system that fires two cylinders at once. One of these cylinders is on its exhaust stroke. That's why its called a wastespark ignition system. One of the sparkplugs firing is "wasted" on the inert exhaust gases.

Answer B is correct. This is a diagram of a wastespark ignition system.

Answer C is wrong. This is a multiport fuel injection system. The PCM actuates two injectors at once. A sequential fuel injection system is more precise; Firing one injector at a time for more precise fuel control.

Answer D is wrong. This is a diagram of a multiport fuel injection system.

8. An engine with a viscous fan clutch is running hot while the engine is idling and the vehicle is at rest. Technician A says this type of fan clutch should be checked for leakage. Technician B says the viscous fan and it's electrical system should be tested for a defective relay resulting in an inoperative fan clutch. Who is correct?

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

8.

Answer A is correct. This type of fan operates with a silicon type fluid, not electricity. A loss of fluid will inhibit the fans operation.

Answer B is wrong. Relays are used in electric fan circuits.

Answer C is wrong. Technician A is correct.

Answer D is wrong. Technician A is correct.

9. A fuel pressure test performed at the fuel rail of a SFI sequential fuel injection engine indicates lower than specified fuel pressure. All of these would cause this test result EXCEPT:

  • A. A poor ground in the pump circuit.
  • B. A kink in the fuel return line.
  • C. A restricted fuel filter.
  • D. A faulty fuel pump.

9.

Answer A is wrong. A poor ground or power condition would result in low fuel pressure.

Answer B is correct. This is an EXCEPT type question. A restricted fuel return line would increase fuel pressure at the rail.

Answer C is wrong. A restricted or clogged fuel filter would result in low fuel pressure at the rail.

Answer D is wrong. A faulty or defective fuel pump would result in low fuel pressure at the rail. This is the most common cause of low fuel pressure.

10. An EFI engine with a Mass Air Flow sensor is scanned and the LTFT is found to be 24% at idle. This percentage decreases as the engine's speed is increased to 1500 rpm. All of the following will result in this fuel trim percentage EXCEPT:

  • A. A faulty oxygen sensor.
  • B. A dripping fuel injector.
  • C. A dirty Mass Air Flow sensor.
  • D. A leaking vacuum line.

10.

Answer A is wrong. This indicates a lean fuel condition. The PCM is adding fuel (positive + fuel trim) to compensate for a lean fuel condition.

Answer B is correct. A leaking or dripping fuel injector will result in a rich air fuel ratio. The PCM will reduce the amount of fuel (negative - fuel trim) by decreasing injector pulse width. This leaking injector would result in negative LTFT.

Answer C is wrong. A dirty MAF sensor will result in positive LTFT. Cleaning a hot wire MAF sensor can correct and restore the sensor's signal to the PCM.

Answer D is wrong. A vacuum leak will result in excessive positive fuel trim. LTFT is a constant and stays in memory after the engine has been shut down. It's obtained from oxygen sensor input while the system is in closed loop.