ASE L1 Advanced Engine Performance Q & A Part 1

ASE Practice Test Questions & Answers with Explanation

1. The fuel control system on the composite vehicle remains in open loop at all times. Technician A says that a faulty IAT sensor could be the problem. Technician B says this could be a loose connection at ECM oxygen sensor signal pin terminal. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is D The fuel control system on the composite vehicle will not enter closed loop until the following conditions have been met:

  • A minimum engine-run time of ten seconds
  • Throttle position less than 80%
  • Coolant temp greater than 68°F
  • Both upstream Oxygen Sensors are switching.

Once these requirements are meet, the system will make the change from open loop to closed loop. Technician A is wrong because the ECM does not use intake air temperature as a qualifier for closed loop operation on the composite vehicle. Terminal 60 of the ECM is the input signal for the downstream oxygen sensor. While a poor connection here could cause a failure of the Catalyst Monitor, it would not prevent closed loop operation. Therefore Technician B’s statement is also incorrect.

2. Fuel pressure on a continuous return injection system is within specifications, but leaks down to zero immediately after the pump stops running. What is the most likely cause of this condition?
A. Defective pump
B. Leaking injector
C. Faulty regulator
D. Restricted fuel return line
The correct answer is C Although three of the responses could be associated with a high leakdown rate, according to the circumstances described in the question, the most likely cause is a faulty regulator. The clue to the correct answer can be ‘immediately,’ as it describes how quickly the leakdown occurs. Normally during cranking, the regulator remains closed, which effectively blocks off the return line. This allows the system to operate with maximum fuel pressure for starting. Once the engine is running, the regulator opens due to the vacuum applied at the regulator port. This causes excess fuel to flow back to the tank. Keep in mind that the question indicated that this was a continuous return system! While a leaking injector or bad check valve in the fuel pump would definitely cause a high leakdown rate, neither condition would cause pressure to drop to zero immediately. However, if the regulator were stuck in the open position, system pressure would bleed off as soon as the pump stopped running. In the case of a restricted return line (response D), this would actually prevent immediate leakdown rather than cause it.

3. There are two Throttle Position Sensors used by the composite vehicle. Technician A says that the use of two sensors allows for a more accurate measurement of throttle position. Technician B says this is a failsafe in case one sensor fails. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A The two throttle position sensors on the composite vehicle work as follows. One sensor has a low voltage at idle, which increases as the throttle is opened. The other sensor has a high voltage at idle, which decreases as the throttle is opened. The ECM uses the opposing measurements of these two sensors to calculate a more accurate value for throttle position. The use of two throttle position sensors is not for failsafe purposes,therefore Technician B is incorrect.

4. All of the following statements regarding the composite vehicle OBD II monitors are true EXCEPT:
A. The comprehensive components monitor is a one trip test
B. A LTFT reading of -30% could cause the fuel control monitor to fail
C. The fuel control, O2 sensor and misfire monitors are ran continuously
D. The EVAP monitor will not run if engine temperature is above 94°F
The correct answer is C The OBD II monitors are diagnostic tests used to evaluate the performance of emissions related components and subsystems. Where the composite vehicle is concerned, the Comprehensive Component Monitor is a one-trip test. This means that the ECM will illuminate the MIL, store a DTC and freeze frame following the first ‘bad’ trip so response A is a true statement. Response B indicated that a LTFT reading of -30% could cause the Fuel Control Monitor to fail. This is a true statement. The key word here is ‘could.’ The Fuel Control Monitor is a two-trip test and the LTFT would have to be at the limit for two consecutive trips before the monitor would fail. Response D is also true. The EVAP Monitor will not run unless engine temperature is below 86°F. If engine temperature is higher than this, as would be the case at 94°F, the ECM will not execute the test. Response C is the false statement because the 02 Monitor is a non-continuous test and runs once per trip.

5. What test is the most effective when checking a PCV system?
A. Shake the valve to see if it rattles
B. Perform an rpm drop test
C. Measure the vacuum signal at the valve
D. Perform a vacuum draw test
The correct answer is D All of these answers are methods of checking PCV system operation. Answer B cannot be performed on a computer controlled vehicle because the idle control will compensate for the RPM drop. Shaking the PCV valve can help uncover a clogged valve, but does not prove that the entire system is working properly. The RPM drop test is only effective for testing the PCV system on older engines without feedback control. Checking the vacuum signal to the PCV valve is another legitimate test, however, it too does not verify efficent operation of the entire system. Only a vacuum draw test can determine how well the PCV system is working, and is therefore fhe most effective method. To perform the draw test you remove the oil fill cap and place the tester in it’s place. Inside the tester is a ball that responds to the level of crankcase vacuum present. If the PCV system is working properly, it will draw a slight vacuum on the crankcase that pulls the ball into the ‘safe’ zone. If a draw tester is not available, the same test can be performed using an index card placed over the oil fill hole. If the PCV system is working as designed, the card should stay in place with the engine idling.

6. A discussion of catalytic converters and their effect on emissions and performance by two Technicians. Technician A says a defective converter will always cause reduced performance. Technician B says a defective catalytic converter can cause high emissions without reducing performance. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B If a catalytic converter becomes chemically inactive it will cause high emissions, but have no affect on performance, so technician A is incorrect. Such a defect would also cause the MIL to come on due to a secondary oxygen sensor code. Performance will only be affected when the converter becomes clogged and causes an exhaust restriction. Technician B is therefore correct.

7. The TSI test is immediately aborted after 10 seconds in the high-speed mode. Technician A says that the engine could be running too lean. Technician B says that the exhaust system may be leaking. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is D If the engine stalls out during the test, or the sum of the CO and C02 readings are less than six percent, the test will be automatically aborted. Since the inspection report shows an RPM reading of 2558, the test was obviously not aborted due to an engine stall. However, notice that CO and C02 are both zero, while 02 is nearly 21%. These readings indicate that the sampling probe was measuring ambient air and not the exhaust gases. The only explanation for this is that the probe either fell out of the tailpipe or was never inserted to begin with. The slight HC reading shown on the report is typical of ambient shop air, which usually contains airborne hydrocarbons.

8. The composite vehicle stalls at idle but restarts. Technician A says an open circuit at pin A of the EGR solenoid could be the problem. Technician B says an open circuit to ECM pin 35 could be the cause. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is D An open circuit at pin A of the EGR solenoid would disable the EGR and would not cause the stalling condition. The EGR valve can cause a vehicle to stall at idle, but it would have to be stuck in the open position for this to occur. The ECM output to the EGR solenoid valve is from pin 35. An open on this circuit would prevent the EGR valve from opening. To cause the EGR to remain open, this connection would have to short to ground. Both Technicians are incorrect.

9. The engine in the composite vehicle will crank but not start. A preliminary diagnosis indicates there is no spark. Technician A says that the ignition module should be replaced. Technician B says that a defective CMP sensor could be the root cause of the problem. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is D The composite vehicle’s ECM controls the six ignition coils directly, eliminating the need for a separate ignition control module, therefore Technian A is wrong. The CMP signals allow the ECM to determine fuel injector and ignition coil sequence, as well as the actual intake valve timing. Loss of one CMP signal will set a DTC, and valve timing will be held at the fully retarded position. If neither CMP signal is detected during cranking, the ECM will store a DTC and disable the fuel injectors, resulting in a no-start condition. Consequently, a faulty CMP sensor will not cause a no-spark condition, which is why technician B is wrong.

10. What conclusion can be drawn from the I/M 240 inspection report shown below.
A. The vehicle passed
B. The vehicle failed for high HC.
C. The vehicle failed for high NOx.
D. The vehicle failed for high HC and CO.
The correct answer is C You can clearly see the vehicle fails the test for Nox. The the NOx trace rides above the cutpoint line throughout most of the drive cycle, therefore the vehicle would fail for excessive NOx emissions. The graphs on the I/M 240 inspection report shows the gas trace (solid line) superimposed over the drive cycle pattern (dotted line). The gas trace indicates the vehicle’s emissions output for each second of the 240-second test. Cutpoints, which are represented by a thin horizontil line on each graph, are the maximum allowable emissions based on the model year of the vehicle and it’s GVWR. Even though emissions may exceed the cutpoints at certain periods during the test, this doesn’t mean that the vehicle fails the test because failures are based on averages.

11. The composite vehicle fails a two-speed idle test due to excessive carbon monoxide. While the engine is running the PCV valve is removed from the valve cover and CO emissions drop below the maximum allowable limit. Technician A says that the engine may have one or more leaking injectors. Technician B says that this test proves the PCV system is working properly. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is C High CO (carbon monoxide) emissions are always the result of a rich mixture. This is because rich mixtures lack the oxygen necessary to promote good combustion. As a result, the carbon in the fuel is converted to carbon monoxide (CO), rather than carbon dioxide (C02). The fact that CO dropped when the PCV valve was removed indicates two things. One, the PCV system is working properly, since it allowed enough air to be drawn into the engine to lean out the mixture and reduce the CO reading. Two, the crankcase is contaminated with fuel. With the PCV valve installed, the fuel-contaminated crankcase vapors are being drawn into the engine, causing the mixture to become too rich, therefore Technician A is correct. Technician B’s statement is equally correct, since leaking injectors would be the most obvious cause for crankcase contamination on the composite vehicle.

12. The composite vehicle won’t shift into 3rd gear. Technician A says that a poor connection at TCM terminal 75 could cause this condition. Technician B says that an open circuit on #2 shift solenoid (SS2)could be the cause of the problem. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is C The electronic transmission in the composite. vehicle uses a pair of TCM-controlled solenoids to control fluid flow to the 1-2, 2-3 and 3-4 shift valves. To make the transmission shift from second to third gear, the TCM activates the #2 shift solenoid (552). Obviously, an open solenoid would prevent the 2-3 shift from occurring, which is why technician A’s answer is correct. The TCM activates the solenoid through a ground driver at terminal 75. A poor connection here would cause the solenoid to remain off, preventing the 2-3 shift. So Technician B’s answer is also correct.

13. A vehicle has a failed CAN communication. Technician A says a shorted CAN harness could be the problem. Technician B says an open terminating resistor could be the cause. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is ATechnician A is correct, if a harness becomes shorted, all or part of the network would be inoperable. Technician B’s answer is incorrect. The CAN harness typically uses a 120-ohm terminating resistor on each end of the twisted pair harness. These are either integral to the controllers or found as separate resistors on the harness. The network will shut down if both resistors are open but will remain operable if only one fails.

14. All of the following statements concerning the composite vehicle’s fuel system are false EXCEPT:
A. Fuel pressure ranges between 45 at idle to 50 at wide-open throttle.
B. The fuel system is a continuous return design.
C. Fuel Pressure should be at least 45 psi immediately after engine shutdown.
D. The fuel injectors are ‘bank fired’.
The correct answer is C This question tests your ability to locate service information efficently. Based on the composite vehicle data, the fuel system is a returnless design with sequentially fired injectors. This would eliminate answers B and D, which state that the system is a continuous return design and that the injectors are ‘bank fired.’ Answer B is also incorrect, since fuel pressure on the composite vehicle is regulated to a constant 50 psi. The composite vehicles fuel pressure should remain at a minimum of 45 psi for at least two minutes following engine shutdown, therefore answer C is correct.

15. Technician A says that low CO and high 02 readings could be the sign of a lean air/fuel mixture. Technician B says that an engine misfire will result in low CO along with high 02 readings. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is C The conditions described by both technicians are consistent with low CO and high 02 readings. With a misfire, the lack of combustion prevents carbon monoxide from forming, while the unused oxygen is simply discharged into the exhaust. When the mixture is lean, there is not enough carbon available to make carbon monoxide. This is why CO virtually disappears on the lean side of the stoichiometric point, and why a lean condition causes an increase in 02 levels. A stoichiometric chart provides a graphic representation of how the exhaust gases interact at various air/fuel ratios. Where CO and 02 are concerned, these gases move in opposite directions in relation to the stoichiometric point (14.7:1) . On the rich side of 14.7:1, carbon monoxide gradually rises due to the lack of oxygen in the mixture. This is why CO is an excellent indicator of a rich condition. At 14.7:1, CO is approximately 0.1 of one percent. As the mixture becomes leaner, CO is barely measurable. In contrast, 02 remains at nearly zero percent on the rich side of 14.7:1, and then rises sharply as the air/fuel ratio becomes leaner.

16. There is no response when the throtte pedal is depressed on the composite vehicle. Technician A says that broken connections at terminals 18 and 19 will create this condition. Technician B says a broken connection at ECM terminal 49 could be the cause. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A The throttle on the composite vehicle is of the ‘drive by wire’ design, using an ECM controlled Throttle Actuator Control (TAC) motor. When this actuator is disabled, the spring-loaded throttle returns to its fast idle position of 15%. A broken connection an ECM pin terminal 49 will cause the loss of the APP sensor signal, but there are two sensors. Both inputs must fail for the throttle to be disabled, therefore Technician B’s answer is incorrect. If the ECM loses both inputs from the throttle position sensors at pins 18 and 19 the TAC will also be disabled. Technician A’a answer is correct.

17. The waveform above was captured in closed loop at 2500rpm from the HO2S 1/2 sensor on the composite vehicle. Technician A says that a clogged PCV valve may be generating this pattern. Technician B says that the waveform could be the result of an unintentional ground in the purge flow control circuit. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is D Neither Technicians are correct. To start with, they failed to realize that the sensor in question was the downstream H02S. In addition, a constant purge problem or dogged PCV valve would cause the upstream H02S voltages to be much higher than indicated by the waveform. Under normal conditions, the voltage from the upstream sensors switch rapidly above and below .450V in dosed loop. If the catalyst has at least 95% conversion efficiency, the signal from the downstream H02S will be relatively flat by comparison. This can be seen in the waveform, and is due to the stability of the oxygen levels in the post converter exhaust gases. If the catalyst is failing however, the post converter gases will contain varying amounts of oxygen. As a result, there will be a significant variation in the frequency and amplitude of the downstream H02S signal in dosed loop.

18. The EFE heater stays energized all the time on an engine with Throttle Body Injection (TBI). Which of the following symptoms would NOT be associated with this condition?
A. Lack of power
B. Spark knock
C. Poor cold driveability
D. Excessive NOx emissions
The correct answer is C A superheated mixture reduces charge density, and can therefore cause the engine to lack power. If the EFE grid remains on over an extended period of time, the grid can eventually melt. When this occurs, it creates a restriction in the induction system that will dramatically reduce engine performance. If the EFE heater remains on all the time, cold driveability will be normal, however, the air/fuel mixture will eventually become superheated. Under this condition, combustion chamber temperatures will increase significantly, resulting in spark knock and higher NOx emissions. Because gasoline does not vaporize well at low temperatures, the air/fuel mixture must be rich when the engine is cold. A rich mixture makes enough fuel available so that even a partially burned charge will allow the engine to run. On port-injected engines, fuel vaporizes easily since it is delivered above the intake valve which is a low-pressure area. However, on throttle body injected engines, fuel is delivered outside the manifold. To improve fuel vaporization, some TBI engines are equipped with an electric heater between the throttle body and intake manifold. The heater is energized when the engine is cold so that the air/fuel mixture is preheated before entering the intake manifold. Once the engine reaches a pre-determined temperature, the heater is turned off At this point, the incoming fuel is vaporized through engine heat. With EFE, the ECM can be programmed with a leaner open loop fuel curve. This reduces HC and CO emissions. EFE also improves cold driveability by providing better mixture distribution at low engine temperatures.

19. All of the following information is typically entered into the computer prior to performing an I/M test EXCEPT:
A. VIN
B. Emissions equipment (based on underhood emissions label)
C. GCWR
D. Engine size
The correct answer is C The first check is to ensure the vehicle can be tested safely, the next step in the I/M inspection process is gathering the proper information. Among the data that must be entered into the computer, is the Vehicle Identification Number (VIN), vehicle make, Gross Vehicle Weight Rating (GVWR), and a list of the factory installed emissions equipment. The Gross Combination Weight Rating (GCWR) indicates the maximum allowable weight of a loaded tow vehicle and trailer. This is not applicable to I/M testing and is therefore not required.

20. A vehicle with multiport fuel injection stall on deceleration. Technician A says that a contaminated throttle body could be the cause of the problem. Technician B says the problem could be from a faulty TCC solenoid. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is C Stalling can result from a variety of conditions and both of the technicians suggestions are valid. All port-injected engines are vulnerable to throttle body contamination. During hard acceleration the crankcase pressure is high and blowby gases are released into the intake air stream. This eventually causes carbon build up on the throttle plate. Over time, this carbon build up reduces the minimum airflow by the throttle plate and the engine stalls before the idle air control valvr can take over. In the case of a faulty TCC (Torque Converter Clutch) solenoid, the clutch could remain in the applied position. Under this condition, there would be no slip between the engine and transmission, resulting in a closed throttle stall. This condition is similar to bringing a vehicle with a manual transmission to a stop in gear without releasing the clutch.

21. Two technicians are discussing emission controls and related failure symptoms. Technician A says that a faulty secondary air system can cause backfiring. Technician B says that if the hot air hose is missing on an engine with a thermostatic air cleaner, NOx emissions will be higher than normal. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is A The secondary air system reduces HC and CO emissions by injecting oxygen into the exhaust manifold when the engine is cold. Once the engine reaches a pre-determined temperature, pump air is diverted to the converter or atmosphere, depending on the system. On vehicles with electric pumps, the ECM simply disables the pump after a certain amount of time has elapsed. If pump air is continuously injected into the exhaust manifold, it can cause a backfire under certain conditions. For example, during heavy acceleration, the ECM pulses the injectors longer to provide a richer mixture. If oxygen is pumped into the manifold during this time, a backfire will result as the excess hydrocarbons are oxidized. This fully supports Technician A’s answer. A thermostatic air cleaner is used to improve fuel vaporization on throttle body injected engines when cold. The damper valve opens the inlet at the base of the air cleaner while blocking the opening at the snorkel. This allows hot air from the exhaust manifold heat stove to be drawn into the engine through a heat-resistant hose. As the fuel comes in contact with the hot air, it vaporizes instantly. Without the TAC system, incoming fuel would condense on the cold throttle plate and puddle inside the intake manifold. If the hot air hose is missing, cold engine performance will be adversely affected, but only when the outside temperature is low. During warm weather, ambient heat provides sufficient fuel vaporization. In order for the TAC system to raise NOx emissions, the hot air hose would need to be in place and the damper stuck in the closed (hot air) position. Therefore Technician B is incorrect.

22. The composite vehicle idles rough and stalls when the transmission is put into gear. Technician A says that the circuit to ECM terminal 35 could have a short to ground. Technician B says that a contaminated throttle body may be the cause of the problem. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is C A contaminated throttle body reduces airflow and causes a drop in engine speed, placing the transmission in gear, activating the A/C compressor, or turning the wheels sharply, can trigger a stall. The EGR valve on the composite vehicle is activated by a manifold vacuum signal from the EGR solenoid. When the solenoid is de-energized, vacuum is blocked and the valve remains closed. Once the conditions are right, the ECM activates the EGR valve by grounding the solenoid at terminal 35. If this circuit were shorted to ground, the solenoid would be on all the time and the EGR valve would be open at closed throttle. This would cause the engine to run rough and stall, especially when placed under load, such as putting the transmission in gear

23. After a road test the technician reveals that the torque converter clutch is not releasing causing the composite vehicle to stall at a stop. Technician A says the problem could be caused by a broken connection at TCM terminal 78. Technician B says a broken connection at ECM terminal 64 could be the cause. Who is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A or B
The correct answer is B The input from the BPP is sent to the ECM, but the TCM uses the input to disengage the TCC. The two modules communicate by way of the serial data link so that the BPP input to the ECM is used by the TCM to disengage the TCC. If the technician looks beyond the
schematic to the operating strategy of the TCM however, he will notice that the TCM is programmed to enter a failsafe operating mode if it can’t communicate with the ECM. In failsafe mode, the transmission remains in second gear and the TCC is disabled. The serial data link is connected to the TCM at terminals 78 and 79. Loss of the connection at either of these terminals will put the TCM in failsafe mode and the TCC would not engage, therefore Technician A is incorrect. The Brake Pedal Position (BPP) switch is located on the brake pedal and doses anytime the brake pedal is pressed. This input is used by the TCM to disengage the Torque Converter Clutch (TCC). When the brake pedal is pressed, the ECM will receive a high voltage input at terminal 64. Loss of this input can prevent disengagement of the torque converter clutch, and technician B is therefore correct.

24. An engine with DI ignition becomes harder to start as ambient temperature drops. Below freezing the engine will not start at all. Technician A says that the coil wire may be bad. Technician B says the problem could be a faulty ignition coil. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is C Although a cold starting problem could be attributed to a variety of conditions, the suggestions made by technicians A and B are among the most likely, and therefore equally correct. This is because falling outside temperatures cause an increase in secondary resistance. To begin with, cranking speed is reduced at low temperatures due to thicker oil and a tighter engine. Since the starter draws more current when the engine is cold, there is less voltage available for the ignition system. Under normal conditions, the module will compensate for the reduced voltage by increasing dwell. However, if the coil is shorted, the developing magnetic field will still be too weak to generate sufficient energy. Consequently, as the outside temperature drops, the engine will be increasingly difficult to start. A high-resistance coil wire could cause the same problem for a different reason. Under this condition, the wire would create an excessive voltage drop, which would consume much of the secondary energy needed to fire the plugs.

25. Oxides of Nitrogen begin to form when combustion temperatures exceed:
A. 1500° F
B. 2000° F
C. 2500° F
D. 3000° F
The correct answer is C The threshold temperature for Oxides of Nitrogen (NOx) to form is 2500°F. Below that temperature nitrogen is inert and this class of emissions will not be produced.

This post was written by: Martin Hand

Donations

If you find this information helpful please consider a donation. These articles, questions and comments are very time consuming so even a small donation gives me motivation to keep educating automotive owners. Donations will allow us to continue open questioning/comments, automotive education and repair tutorials in the future as the business grows. All proceeds go to the expansion and maintenance mdhmotors.com. Thank You



Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.