ASE A8 Engine Performance Practice Test

25 practice questions

Choose an answer, then check it under Show answer.

1. Question 1 of 25Hard

   A technician is evaluating an engine using an oscilloscope connected to an in-cylinder pressure transducer installed in cylinder 1 while the engine idles. Technician A says a retarded camshaft will cause the exhaust valve opening (EVO) event to occur earlier than normal on the waveform time scale. Technician B says an exhaust system restriction will cause the pressure during the exhaust stroke to rise significantly above the 0 psig atmospheric baseline. Who is correct?

   1. AA. A only
   2. BB. B only
   3. CC. Both A and B
   4. DD. Neither A nor B
   Show answer to question 1

   Answer: B. B only

   Technician B is correct because backpressure caused by a restricted exhaust system prevents spent gases from leaving easily, forcing the pressure plateau during the exhaust stroke to rise above atmospheric pressure (0 psig). Technician A is wrong because camshaft timing that is retarded causes all valve timing events, including exhaust valve opening, to occur later on the horizontal time grid, not earlier.

2. Question 2 of 25Hard

   A technician connects a dual-trace digital storage oscilloscope (DSO) to DLC terminal 6 (CAN-H) and terminal 14 (CAN-L) to diagnose a high-speed CAN network issue. Technician A says if the waveform shows CAN-H and CAN-L mirroring each other in opposite directions from a 2.5-volt baseline, the two bus lines are shorted together. Technician B says if CAN-H is shorted to chassis ground, CAN-H voltage will read approximately 5.0 volts continuously. Who is correct?

   1. AA. A only
   2. BB. B only
   3. CC. Both A and B
   4. DD. Neither A nor B
   Show answer to question 2

   Answer: D. Neither A nor B

   Neither technician is correct. Symmetrical mirroring in opposite directions from a 2.5-volt baseline (CAN-H pulsing upward to 3.5 volts while CAN-L pulses downward to 1.5 volts) represents normal, healthy differential communication; a short between the two lines would cause both traces to collapse together into a single flat or identical trace. Technician B is incorrect because a short to chassis ground pulls the CAN-H circuit to 0.0 volts, not 5.0 volts.

3. Question 3 of 25Easy

   A vehicle has poor fuel economy and black exhaust smoke. The scan tool displays an Engine Coolant Temperature (ECT) reading of -40°F (-40°C) on a warmed-up engine. When the technician disconnects the ECT sensor harness and jumps the signal circuit to the sensor ground circuit with a fused jumper, the scan tool reading changes to 284°F (140°C). Which of these is the MOST likely cause?

   1. AA. An internal analog-to-digital converter failure in the PCM
   2. BB. An open circuit in the sensor signal wiring harness
   3. CC. A failed ECT sensor with an internal open circuit
   4. DD. A short to ground in the sensor reference voltage wire
   Show answer to question 3

   Answer: C. A failed ECT sensor with an internal open circuit

   A reading of -40°F indicates an open circuit (high voltage) on a standard negative temperature coefficient (NTC) sensor circuit. Because jumping the signal wire to the sensor ground causes the scan tool to display maximum temperature (near zero volts), the signal wire, ground wire, and PCM internal pull-up circuit are proven intact, meaning the open circuit is located inside the sensor itself. If there were an open in the harness signal wire or a PCM failure, jumping the connector pins would not have changed the displayed temperature.

4. Question 4 of 25Medium

   When diagnosing an electric secondary air injection (AIR) pump that fails to operate during an active scan-tool test, all of the following circuit faults could be the cause EXCEPT:

   1. AA. A short-to-ground in the pump motor ground return circuit
   2. BB. A blown high-current power feed fuse to the relay switch contacts
   3. CC. High electrical resistance across the closed contacts of the pump relay
   4. DD. An open circuit in the pump motor ground wire
   Show answer to question 4

   Answer: A. A short-to-ground in the pump motor ground return circuit

   The pump motor ground return circuit is already designed to connect directly to chassis ground; therefore, an unintended short-to-ground along that wire will not disrupt current flow or prevent the pump from operating. In contrast, an open ground wire breaks the circuit, a blown fuse eliminates input power, and high resistance across the relay contacts causes excessive voltage drop, all of which will prevent the motor from running.

5. Question 5 of 25Medium

   An engine idles roughly, and scan data shows a positive long-term fuel trim near its limit at idle and near zero at 2,500 rpm. When the technician disconnects the PCV valve from the valve cover and plugs the hose, the fuel trim returns to normal. Which is the MOST likely cause?

   1. AA. The air filter is restricted
   2. BB. The exhaust manifold is leaking
   3. CC. The PCV valve is clogged closed
   4. DD. The PCV valve is stuck open
   Show answer to question 5

   Answer: D. The PCV valve is stuck open

   A PCV valve stuck open acts like a vacuum leak at idle, so the fuel trim goes positive; plugging the hose removes that extra air and the trim returns to normal. A clogged PCV valve would cause crankcase pressure, not a lean idle.

6. Question 6 of 25Hard

   A lab scope current probe on the primary circuit of one coil-on-plug shows its current ramp rising much faster than the other coils and reaching the driver's current limit sooner. The coil's primary resistance is within the manufacturer's specification. Which of these is the MOST likely cause?

   1. AA. High resistance in the coil ground circuit
   2. BB. An open secondary winding
   3. CC. A spark plug gap that is too small
   4. DD. Shorted turns in the primary winding
   Show answer to question 6

   Answer: D. Shorted turns in the primary winding

   Shorted primary turns reduce the winding's inductance, so current rises faster and reaches the driver's current limit sooner. Primary resistance can still appear within specification because only a few turns may be shorted. High resistance in the ground circuit would slow the current rise rather than speed it up.

7. Question 7 of 25Hard

   Two technicians are discussing OBD II monitor enable criteria and drive cycles. Technician A says enable criteria are the specific operating conditions, such as coolant temperature and fuel level, that must be present before the PCM will run a non-continuous monitor. Technician B says an OBD II warm-up cycle requires the engine coolant temperature to rise at least 40 degrees F (22 degrees C) after starting and reach at least 160 degrees F (71 degrees C). Who is correct?

   1. AA. A only
   2. BB. B only
   3. CC. Both A and B
   4. DD. Neither A nor B
   Show answer to question 7

   Answer: C. Both A and B

   Both technicians are correct. Technician A is correct because enable criteria are the pre-programmed conditions (e.g., intake air temperature, engine load, speed, and fuel tank level between 15% and 85%) required for the PCM to initiate a self-test monitor. Technician B is correct because the standardized OBD II definition of a warm-up cycle is an engine start during which the coolant temperature rises at least 40 degrees F and reaches a minimum operating temperature of 160 degrees F.

8. Question 8 of 25Easy

   A technician removes the PCV valve from the valve cover with the hose still attached and, with the engine idling, places a finger over the valve inlet. Which result indicates that the valve and hose are flowing?

   1. AA. Oil is drawn out of the valve cover.
   2. BB. The engine idle speed drops or the engine stumbles.
   3. CC. The manifold vacuum reading at the valve increases steadily.
   4. DD. The engine idle speed remains exactly the same.
   Show answer to question 8

   Answer: B. The engine idle speed drops or the engine stumbles.

   With the valve and hose flowing, the PCV valve admits extra air into the intake; covering the inlet removes that air and changes idle quality. If the valve or hose were restricted, covering the inlet would have little or no effect on idle.

9. Question 9 of 25Medium

   After a tune-up, an engine runs rough and backfires through the intake at idle. A technician finds that two spark plug wires are crossed at the distributor cap. Which of these does this condition cause?

   1. AA. The coil dwell time is shortened by the control module
   2. BB. The spark plugs fire with too much advance at all speeds
   3. CC. Cylinders fire out of the correct firing order
   4. DD. The ignition coil produces excessive secondary voltage
   Show answer to question 9

   Answer: C. Cylinders fire out of the correct firing order

   Crossed wires send spark to the wrong cylinder at the wrong point in the firing order, so combustion can occur while the intake valve is still open and the flame exits through the intake. Wire routing does not change coil output or dwell, and timing advance is not altered at all speeds by swapping two wires.

10. Question 10 of 25Hard

    An engine runs well, but there is pronounced radio static that increases with engine speed. The capacitor connected across the ignition coil primary is found to be open. Which of these best describes the effect of this fault?

    1. AA. Radio noise and driver stress may increase
    2. BB. Timing will stay fixed at base timing
    3. CC. Spark will be lost at all cylinders
    4. DD. Primary current will stop when the engine is cold
    Show answer to question 10

    Answer: A. Radio noise and driver stress may increase

    The primary capacitor suppresses radio frequency interference and helps protect the switching components, so an open capacitor can increase radio noise and stress the coil driver. It does not by itself stop spark or lock timing, which are functions of the coil secondary and the PCM control strategy.

11. Question 11 of 25Medium

    A vehicle sets DTC P0128, coolant thermostat below regulating temperature. After 15 minutes of driving in 70°F ambient temperature, the scan tool shows engine coolant temperature at 150°F, and an infrared thermometer confirms the coolant at the thermostat housing is actually 150°F. Which of these is the MOST likely cause?

    1. AA. A coolant temperature sensor reading too low
    2. BB. A low coolant level in the system
    3. CC. A cooling fan that runs continuously
    4. DD. A thermostat that is stuck open
    Show answer to question 11

    Answer: D. A thermostat that is stuck open

    The infrared reading confirms the coolant really is cold, so the sensor signal is accurate and the engine is not reaching regulating temperature, which points to a thermostat stuck open. A skewed sensor would show a low reading on the scan tool while the measured coolant temperature was normal.

12. Question 12 of 25Medium

    A PCM-controlled engine has a poor ground at the PCM case. Technician A says to voltage-drop test each PCM ground circuit with the PCM connected and the key on, engine running, and expect less than about 0.1 volt. Technician B says an ohmmeter reading of 0.5 ohm from the PCM ground pin to the battery negative post proves the ground circuit is good. Who is correct?

    1. AA. A only
    2. BB. B only
    3. CC. Both A and B
    4. DD. Neither A nor B
    Show answer to question 12

    Answer: A. A only

    The ground circuit must be tested under load, and a good PCM ground typically shows less than 0.1 volt drop. A 0.5-ohm reading may look small, but an ohmmeter does not load the circuit and can miss a connection that drops voltage once current flows; that reading alone does not prove the ground is good.

13. Question 13 of 25Medium

    With all modules asleep, key-off current is 210 mA. Removing the fuse for the audio amplifier drops the current to 15 mA. Which is the MOST likely cause?

    1. AA. The alternator has a shorted diode
    2. BB. The amplifier is staying powered after the sleep command
    3. CC. The ignition switch is stuck in the accessory position
    4. DD. The battery has high internal resistance
    Show answer to question 13

    Answer: B. The amplifier is staying powered after the sleep command

    The current drop when the amplifier fuse is removed identifies that circuit as the drain source. A shorted alternator diode would not be affected by removing the amplifier fuse.

14. Question 14 of 25Easy

    A customer reports that the engine sometimes stalls while driving. All of the following are appropriate when verifying the complaint EXCEPT:

    1. AA. Checking for aftermarket accessories or recent service work that could affect the complaint
    2. BB. Asking whether any warning light came on before or after the stall
    3. CC. Asking the customer whether the stall occurs at idle, during acceleration, or at steady speed
    4. DD. Replacing the crankshaft position sensor before attempting to duplicate the stall
    Show answer to question 14

    Answer: D. Replacing the crankshaft position sensor before attempting to duplicate the stall

    Verifying the complaint means gathering details and trying to reproduce the condition before replacing parts. Asking about the operating conditions and warning lights helps narrow the cause, while replacing a sensor first is a guess that may not address the stall.

15. Question 15 of 25Medium

    A technician inspecting the fuel hoses on a port fuel injection vehicle finds a rubber hose that is soft and swollen near its connection, with a faint fuel odor. What should the technician do?

    1. AA. No action is needed, since slight swelling is normal.
    2. BB. Loosen the clamp, which is over-tightened.
    3. CC. Replace the hose with one rated for the system pressure.
    4. DD. Clean the hose and reinstall it with a new clamp.
    Show answer to question 15

    Answer: C. Replace the hose with one rated for the system pressure.

    Soft, swollen hose on a pressurized fuel system indicates deterioration, and the fix is replacement with hose rated for the pressure and fuel blend used. An over-tightened clamp is the tempting distractor, but clamp torque does not cause a hose to soften and swell along its length.

16. Question 16 of 25Medium

    A technician connects a vacuum gauge to an intake manifold port to test for an exhaust system restriction on an engine that lacks power under load. Technician A says if the vacuum reading drops sharply upon rapid acceleration and then immediately recovers, an exhaust restriction is present. Technician B says if the engine speed is held steady at 2,500 RPM and the vacuum reading gradually drops toward zero, an exhaust restriction is present. Who is correct?

    1. AA. A only
    2. BB. B only
    3. CC. Both A and B
    4. DD. Neither A nor B
    Show answer to question 16

    Answer: B. B only

    Technician B is correct because an exhaust restriction traps burned gases in the cylinders, reducing intake manifold vacuum steadily while engine speed is held at a higher RPM. Technician A is wrong because a momentary vacuum drop during rapid throttle opening followed by a quick return to normal is the expected behavior of a healthy engine.

17. Question 17 of 25Medium

    A technician applies compressed air to cylinder 1 at top dead center (TDC) compression during a cylinder leakage test and measures 45% leakage. Air is heard flowing out of the oil dipstick tube. Which of these is LEAST likely to cause this condition?

    1. AA. Broken compression rings
    2. BB. A holed piston crown
    3. CC. A cracked intake valve face
    4. DD. A severely scored cylinder wall
    Show answer to question 17

    Answer: C. A cracked intake valve face

    A cracked intake valve face allows pressurized air to escape into the intake runner and out through the throttle body or air intake, not into the crankcase or oil dipstick tube. Broken rings, a hole in the piston crown, and scored cylinder walls all allow air to leak past the piston assembly directly into the crankcase, resulting in air hissing out of the dipstick tube and oil filler neck.

18. Question 18 of 25Medium

    A starter current draw test shows current within the manufacturer's specification, but the engine cranks slowly and battery voltage during cranking is lower than specification. Which action is MOST appropriate?

    1. AA. Recharge or replace the battery and retest.
    2. BB. Replace the starter solenoid.
    3. CC. Replace the starter.
    4. DD. Check the ignition timing.
    Show answer to question 18

    Answer: A. Recharge or replace the battery and retest.

    Normal starter current with low cranking voltage and slow cranking points to a battery that is discharged or unable to supply current under load. The battery should be recharged, load tested, and the starter draw retested before replacing starter components. Ignition timing does not cause low cranking voltage.

19. Question 19 of 25Medium

    A technician clears the DTCs with a scan tool after retrieving them. Which of these is also erased by this action?

    1. AA. The vehicle identification number programmed into the powertrain control module
    2. BB. The calibration identification stored in the powertrain control module
    3. CC. The freeze frame data and the readiness status of the non-continuous monitors
    4. DD. The permanent DTC memory stored in the powertrain control module
    Show answer to question 19

    Answer: C. The freeze frame data and the readiness status of the non-continuous monitors

    Clearing codes erases stored and pending DTCs together with the freeze frame and resets the non-continuous monitors to Not Ready. Permanent codes are not erased by a scan tool clear; they clear only after the monitor runs and passes on a later drive cycle.

20. Question 20 of 25Hard

    Two technicians are discussing air/fuel ratio sensor testing. Technician A says a wideband air/fuel ratio sensor produces a pump-current signal that the control module interprets as an air/fuel ratio. Technician B says a wideband air/fuel ratio sensor should toggle rapidly between 0.1 volt and 0.9 volt like a conventional oxygen sensor. Who is correct?

    1. AA. A only
    2. BB. B only
    3. CC. Both A and B
    4. DD. Neither A nor B
    Show answer to question 20

    Answer: A. A only

    Technician A is correct because a wideband air/fuel ratio sensor uses a pump current that the control module converts into a lambda or air/fuel ratio value. Technician B is wrong because a wideband sensor does not produce the rapid 0.1-to-0.9-volt switching pattern of a conventional zirconia oxygen sensor.

21. Question 21 of 25Hard

    A vehicle is brought in for poor acceleration. A vacuum gauge connected to intake vacuum reads a steady 17 in-Hg at idle, but on a snap throttle the reading drops to about 2 in-Hg and returns to 17 slowly. Which condition is MOST likely?

    1. AA. A restricted exhaust system
    2. BB. Worn piston rings and cylinder walls
    3. CC. A leaking intake manifold gasket
    4. DD. Retarded base ignition timing
    Show answer to question 21

    Answer: A. A restricted exhaust system

    Vacuum should drop on a snap throttle and snap back quickly; a slow, labored return is the classic sign of backpressure from a restricted exhaust. Worn rings cause a low steady reading rather than a slow recovery, and a leaking intake gasket makes the idle reading low or unsteady.

22. Question 22 of 25Easy

    All of the following are likely symptoms of a partially restricted catalytic converter EXCEPT:

    1. AA. Higher-than-specified exhaust backpressure
    2. BB. Reduced engine power during acceleration
    3. CC. A converter that glows after a short drive
    4. DD. Improved fuel economy at highway speed
    Show answer to question 22

    Answer: D. Improved fuel economy at highway speed

    A restricted converter raises exhaust backpressure, reduces power, and can cause the converter to overheat and glow. Fuel economy would worsen rather than improve because the engine must work harder to push exhaust through the restriction.

23. Question 23 of 25Easy

    A vehicle intermittently hesitates and stalls while driving. An oscilloscope connected to a low-amp current probe clamped around the fuel pump power feed wire displays an average current draw of only 1.5 amps, with regular, repeating dropouts to zero amps every eighth commutator segment. Which of these is the MOST likely cause?

    1. AA. A burned and shorted fuel pump relay coil
    2. BB. An open commutator segment in the fuel pump armature
    3. CC. High mechanical friction in the fuel pump motor bearings
    4. DD. A restricted fuel filter element in the supply line
    Show answer to question 23

    Answer: B. An open commutator segment in the fuel pump armature

    A healthy automotive electric fuel pump typically draws 4 to 8 amps with smooth, repeating wave crests as brushes pass each commutator segment. An open or worn commutator segment produces a sharp, rhythmic drop to zero amps once per motor revolution along with low overall average current. High mechanical friction causes excessively high current draw, while a restricted fuel filter or shorted relay coil will not create periodic dropouts tied to motor rotation.

24. Question 24 of 25Easy

    All of the following are approved procedures when inspecting or servicing a conventional pleated paper engine air filter element EXCEPT:

    1. AA. Holding a bright inspection light on the dirty side while viewing the clean side to detect paper pinholes or tears
    2. BB. Directing high-pressure compressed air through the filter element from the clean side to blow out accumulated dust
    3. CC. Inspecting the rubber or polyurethane perimeter sealing gasket for crushing, tears, or hardening
    4. DD. Wiping out loose dirt, leaves, and debris from inside the lower airbox housing before installing the new filter
    Show answer to question 24

    Answer: B. Directing high-pressure compressed air through the filter element from the clean side to blow out accumulated dust

    High-pressure compressed air should never be used to clean a pleated paper filter element because it tears the delicate microfibers and opens invisible pores, allowing unfiltered dirt to enter the engine. Holding an inspection light behind the filter to check for light passing through tears, cleaning the housing prior to installation, and checking the perimeter seal for integrity are all proper service practices.

25. Question 25 of 25Easy

    A technician installs a replacement powertrain control module in a vehicle. Which of these must be done before the vehicle is returned to service?

    1. AA. Drive the vehicle at highway speed until all monitors are complete.
    2. BB. Disconnect the module and clean all terminals with dielectric grease.
    3. CC. Program the module with the correct calibration and vehicle-specific configuration.
    4. DD. Install the old module's PROM into the new module to transfer the calibration.
    Show answer to question 25

    Answer: C. Program the module with the correct calibration and vehicle-specific configuration.

    Replacement control modules generally must be programmed with the correct factory calibration and configured with vehicle-specific data such as VIN, tire size or axle ratio. Current modules use flash memory, so transferring a PROM is not the correct procedure, and driving the vehicle does not program the module.

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