ASE A8 Engine Performance Practice Test

21. The MAP sensor's vacuum hose is loose and cracking. Technician A says this sensor measures air mass to establish the fuel injector's base pulse width. Technician B says this sensor measures changes in intake manifold pressure. Who is correct?

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

21.

Answer A is wrong. A (MAP) manifold absolute pressure sensor senses intake manifold pressure. Many contain a barometer to sense altitude.

Answer B is correct. This pressure sensor is often connected to the intake manifold by a short vacuum hose. It's different from a MAF sensor; the MAP senses manifold air pressure and the MAF senses air mass.

Answer C is wrong. Technician B is correct.

Answer D is wrong. Technician B is correct.

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22. A misfire is detected at the #3 cylinder of a COP ignition system. There is no power at the Bat+ terminal of the coil. Which of the following is the MOST likely cause of this condition?

  • A. Resistance in the primary circuit.
  • B. Resistance in the secondary circuit.
  • C. A leak in the secondary insulation.
  • D. An open between the coil and it's power source.

22.

Answer A is wrong. If there is no power at the BAT+ terminal, the primary circuit would not be energized. Resistance in the #3 primary circuit will result in weak spark at that cylinder.

Answer B is wrong. Resistance in the secondary or boot will result in leaking spark at that cylinder.

Answer C is wrong. A COP ignition system eliminates the distributor and the secondary ignition wires.

Answer D is correct. This is the most likely cause of a no spark condition at the #3 cylinder. An open in the power wire between the power source, ground, or PCM and the coil would result in no spark at the cylinder.

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23. The OBD II Enhanced Evaporative Emissions monitor has illuminated the check engine light and set fault code P0457 indicating that a gross leak has been detected. Which of the following is the MOST likely cause of this leak?

  • A. A crimp in the vent hose.
  • B. A saturated canister.
  • C. A stuck closed purge valve.
  • D. A loose fuel filler cap.

23.

Answer A is wrong. The vent valve is a normally open valve. Blockage like a kink in the vent hose would restrict fresh air flow into the canister.

Answer B is wrong. A saturated canister will not result in a gross leak detected code.

Answer C is wrong. The purge valve is a normally closed valve that vents fuel vapor into the intake manifold when activated. This valve is not the most likely cause for a gross leak detected code.

Answer D is correct. It's wise to check the condition of the fuel tank's fuel filler cap before preceding. A loose cap will result in a gross leak detected code. It's actually the most common fault found in the enhanced EVAP system. Some systems illuminate a unique loose gas cap light on the instrument panel whenever this code is detected.

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24. A vehicle with a four cylinder EFI engine has poor acceleration. Scan tool data indicates the engine has a LTFT of -19 % at idle indicating a rich air fuel ratio. Technician A says too much fuel in the air fuel mixture will damage the substrate of the catalytic converter. Technician B says a LTFT of -19 % indicates the PCM is adding fuel to the air fuel ratio. Who is correct?

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

24.

Answer A is correct. A rich fuel mixture will result in excess unburned fuel (HC's) entering the catalytic converter causing it to overheat.

Answer B is wrong. When a - minus precedes the percentage it's subtracting fuel. A LTFT of -19 % means the PCM is reducing injector pulse width. The PCM's O2 sensor is indicating a low oxygen content in the exhaust stream. It will compensate for this rich signal by leaning the mixture to return STFT to it's correct range.

Answer C is wrong. Technician A is correct.

Answer D is wrong. Technician A is correct.

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25. A vehicle has a fuel trim of -5 % at idle and -25 % at cruise. Scan tool data indicates a steady oxygen sensor output voltage of 800Mv. When a vacuum hose is disconnected from the intake manifold, there is no change in the oxygen sensor's voltage. This condition is caused by:

  • A. An intake manifold leak.
  • B. A faulty throttle position sensor.
  • C. A faulty oxygen sensor.
  • D. A kink in the fuel return line.

25.

Answer A is wrong. A leaking intake manifold results in a lean fuel condition. The PCM is adding fuel to the mixture, but when the vacuum hose is disconnected from the intake manifold the O2 sensor should sense this change.

Answer B is wrong. The PCM uses the TPI to indicate throttle position. The computer is adding fuel to the mixture, but when the vacuum hose is disconnected from the manifold the oxygen sensor should sense this change.

Answer C is correct. A faulty or stuck oxygen sensor can result in a rich fuel condition and would not change its output when a vacuum hose is removed.

Answer D is wrong. A restricted fuel return line will result in a rich fuel mixture, but when the vacuum hose was removed, the oxygen sensor readings should have changed toward lean or below 500Mv.

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