ASE L1 Advanced Engine Performance Q & A Part 3

ASE Practice Test Questions & Answers with Explanation

1. On the composite vehicle the CAN terminating resistors are located
A. In the CAN harness
B. In the ECM and the Instrument Cluster
C. In the ECM and the Immobilizer module
D. In the TCM and the instrument cluster
The correct answer is B The wiring schematic for the composite vehicle shows that the CAN terminating resistors are integral to the ECM and the Instrument Cluster, even though terminating resistors can be separate components on the ends of the CAN harness.

2. A kinked vacuum line at the fuel pressure regulator could cause:
A. Long engine crank times
B. High NOx emissions
C. An off-idle hesitation
D. Poor fuel economy
The correct answer is D In most continuous return injection systems, the pressure regulator responds to changes in engine load based on a manifold vacuum signal. If the vacuum line to the regulator becomes kinked, fuel pressure will increase. This is because the regulator closes off the fuel return line and increases fuel pressure as vacuum drops. While the increase in fuel pressure most likely will not create any driveability problems, the vehicle owner will eventually notice a reduced fuel economy. Long crank times are generally the result of an excessive fuel leakdown rate. The pressure regulator could lengthen crank times if it were stuck in the open position. Since a kinked vacuum line would prevent the regulator from opening, and because the vacuum signal to the regulator is too low during cranking to affect its operation, answer A is incorrect. answers B and C describe a symptom of a lean air/fuel ratio, and are therefore both are incorrect.

3. An engine pings excessively under acceleration. All of the following conditions could cause this EXCEPT:
A. EGR valve stuck closed
B. Improper antifreeze concentration
C. Missing thermostat
D. Missing catalytic converter
The correct answer is C Engine ping, technically known as spark knock, is the result of excessive combustion chamber temperatures. Consequently, any condition that raises engine temperature has the potential to cause spark knock. For example, if the ratio of antifreeze to water is too great, the coolant will not release heat efficiently as it flows through the radiator. As the coolant retains more and more heat, combustion temperatures gradually rise high enough to ignite the air/fuel mixture spontaneously. This condition creates multiple flame fronts in the chamber that eventually collide, resulting in the metallic rattling sound commonly referred to as ‘engine pinging.’ Combustion chamber temperatures are also controlled through EGR (Exhaust Gas Recirculation). The EGR valve, which allows metered amounts of exhaust gas to dilute the air/fuel mixture. The exhaust gas is non-reactive, EGR causes the air/fuel charge to become weaker in return reducing combustion temperatures. Obviously, if the EGR valve was stuck in the closed position, combustion temperatures would rise quickly, since charge dilution would cease. On many engines, a missing catalytic converter will prevent the EGR valve from opening. This is because many vacuum operated EGR valves require sufficient exhaust backpressure to operate properly. That’s why a missing converter can also cause spark knock. A thermostat regulates the engine’s minimum operating temperature. In cases where the thermostat is stuck open or has been removed, the engine will run cold. Consequently, a missing thermostat would not cause spark knock.

4. Two technicians are discussing the fuel injector waveform shown here. Technician A says that the rise in control circuit voltage is normal. Technician B says that the waveform is typical of a peak and hold injector. 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 The waveform accompanying the question was taken from an injector controlled by a saturated switch driver. This is evident in the single inductive spike immediately following the injector-OFF signal. A peak and hold injectors generate two inductive spikes; one following the initial pulse, and another less powerful spike that follows the current limiting pulse, therefore Technician A is incorrect. Technician B is also incorrect. Once a saturated switch driver grounds the injector control circuit, voltage should drop to nearly zero and remain there for the duration of the pulse. However, if there is high resistance in the control circuit, a portion of the supply voltage will be applied to the additional resistance. Under this condition, there is less voltage available to activate the injector. This can be seen as a rise in control circuit voltage during the injector pulse. Notice also that the inductive spike is lower than normal due to the voltage drop in the control circuit. High resistance can be caused by several conditions including, any loose or corroded connectors between the injector and ECM, damaged control circuit wiring, or a poor connection at the ECM. If all of the injectors are affected similarly, the most likely cause is a bad ECM ground.

5. All of the following conditions could cause an increase in HC (hydrocarbon) emissions EXCEPT:
A. EGR valve stuck closed
B. A missing air pump drive belt
C. EGR valve not seating
D. EVAP system leak
The correct answer is A Hydrocarbons are created from unburned fuel during the combustion process. HC can also be released into the atmosphere due to evaporating fuel. A leaking EVAP system could cause excessive HC, since the evaporative emissions system is designed to contain fuel vapor. Under normal conditions, an engine will emit a small amount of HC due to temperature variations in the cylinder. Post combustion controls, like secondary air and the catalytic converter, are designed to burn this residual HC. That’s why a missing air pump drive belt could cause HC emissions to increase. The most common cause of high HC is a cylinder misfire. Whenever combustion is incomplete or fails to occur at all, high levels of unburned fuel are discharged into the exhaust. While the causes of misfiring are many, they can be broadly defined as being either electrical or mechanical. An EGR valve that fails to seat properly is one of the many types of mechanical misfires. Under this condition, the air/fuel mixture becomes too weak to burn because it is largely displaced by exhaust gas. The exhaust gas does not contain the oxygen necessary to support combustion and the engine will misfire causing high levels of hydrocarbons. The purpose of the EGR valve is to reduce oxides of nitrogen (NOx). If the valve is stuck in the closed position, it will have no effect on hydrocarbons. Rather, a valve that is stuck closed will cause NOx emissions to rise dramatically.

6. The downstream oxygen sensor signal is switching consistently with the upstream oxygen sensors. The Malfunction Indicator Light (MIL) is on and the composite vehicle has high emissions.Technician A says the downstream oxygen sensor could be defective. Technician A says a faulty catalytic converter could be 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 BThe varying voltage indicates that the downstream oxygen sensor is active and functional and therefore technician A is incorrect. The downstream oxygen sensor monitors catalytic converter condition and will show steady low voltage readings if the converter is chemically active and reducing emissions. The varying voltage of the downstream sensor consistent with upstream oxygen sensor readings is an indication that the catalytic converter is no longer chemically active, therefore Technician B is correct.

7. A vehicle with TBI (Throttle Body Injection) failed the ASM5015 test based on the following Vehicle Inspection Report (VIR). Technician A says that the engine may have a leaking throttle body gasket. Technician B says that the gas readings could be the result of a bad catalytic converter. 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 When an air leak occurs on a throttle body injected engine, it causes an increase in dosed-throttle rpm. This is because the MAP sensor detects the additional airflow and signals the ECM to increase injector pulse width. However, this condition has no real impact on emission levels, since the air/fuel ratio remains the same. This is why technician A’s answer is incorrect. Technician B’s answer is non conclusive but correct. Although the HC and CO readings shown on the VIR are indicative of a slightly rich mixture, these elevated readings could just as easily be the result of a failing converter. For example, let’s assume the closed loop system is in control. That means the ECM will compensate for any condition that could cause a slight bias in the air/fuel ratio. In the case of a slight rich bias, the ECM will reduce injector pulse width to maintain a 14.7:1 air/fuel ratio. Consider also that while NOx emissions are below the legal limit, a good converter will normally do a better job at reducing NOx than the VIR indicates, especially if the mixture is biased rich.

8. The radiator fan is not turning on causing the composite vehicle to overheat. Turning on the air conditioner won’t turn on the fan. Technician A says that an open circuit to pin 6 of the ECM could be the cause. Technician B says a blown fuse number 4 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 Fuse No. 4 powers the fan relay, but it also powers numerous other components, including the fuel injectors, fuel pump relay, and ignition coils. A blown fuse No. 4 would prevent the vehicle from starting, therefore Technician B is incorrect. The fan relay is energized when the ECM completes a low voltage circuit to the fan control relay from pin 6. An open on this circuit would prevent fan operation, therefore Technician A is correct.

9. The composite vehicle will not start. Cranking speed is above 250 rpm. The PID’s shown above were observed by two technicians under KOEO conditions at closed throttle.Technician A says that a failed MAP sensor may be the cause of the no start. Technician B says that the system is stuck in clear flood mode. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is D The complexity of today’s vehicles often causes technicians to overlook the obvious. Virtually all of the displayed values are normal, with the exception of the 0% reading under the fuel tank level PID. The vehicle is out of fuel, which is an obvious reason why the vehicle won’t start. Technician A’s assertion that the system is stuck in the clear flood mode is incorrect, since the values for TP 1 and TP2 accurately reflect the closed throttle conditions. Under KOEO conditions, manifold pressure is equal to atmospheric pressure. This is why the MAP value is 101 kPa (14.7 psi), therefore Technician B’s answer is also incorrect.

10. When shifted into a drive range the composite vehicle stalls but restarts immediately. Technician A says an open fuse 72 could be the cause. Technician B says the wire to pin 72 of the TCM is shorted to ground. 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 BA grounded wire from pin 72 of the TCM would keep the TCC engaged and the vehicle would stall when a drive range is engaged, therefore Technician B is correct. Fuse No. 72 supplies voltage to the shift solenoids and the pressure control solenoid as well as the TCC solenoid. If this fuse should fail the transmission would not engage a drive range. Technician A is therefore incorrect.

11. Two technicians are discussing a snap-throttle test for evaluating ignition system performance. Technician A says that using a spark tester is a more efficient way of to test the ignition system. Technician B says that this test is more useful on port fuel injection than it is for throttle body injection. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is A A snap throttle test places a load on the ignition system that can help isolate problems such as a bad wire or faulty spark plug. When the throttle is opened suddenly, air rushes into the cylinder while the fuel lags behind. This is because fuel is heavier than air. Since the fuel is the conductive material in the mixture, a snap throttle test drives the engine lean, which creates additional secondary resistance. If the ignition system is operating normally, the firing lines should spike upward 4-6kV. However, if a spark plug is gaped too wide, or a wire has excessive resistance, the firing line from the affected cylinder will rise much higher as the coil attempts to initiate the spark. A snap throttle test is most useful for engines with throttle body injection, since fuel lag time is much greater in a ‘wet-manifold’. Fuel is delivered too quickly for a snap throttle test to be very useful on port-injected engines. That’s why using a spark tester is a better way to test the ignition system, regardless of fuel system type. A spark tester is a full proof method for checking ignition system performance since it requires 25k or more to jump the gap. Even better is an adjustable gap spark tester.

12. The composite vehicle is running poorly and has a flashing MIL. Technician A says the condition could be due to an open fuse No. 4. Technician B says a broken circuit to ECM terminal 9 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 A flashing MIL indicates a misfire severe enough to damage the catalytic converter. Pin 9 is the low voltage connection for coil number 5. Loss of this connection will cause a misfire and shut down the ignition coil, therefore Technician B is correct. Fuse No. 4 supplies voltage to all six ignition coils. If this fuse opens, all six ignition coils will be inoperable and the engine would not start. Technician A is incorrect.

13. A multiport fuel injection vehicle only starts with the throttle held open. The vehicle history indicates that the engine has never been serviced except for an occasional oil change and it has about 80,000 miles on it. The MFI system uses an Idle Air Control Valve to regulate closed throt­tle rpm. Technician A says that the problem may be the result of a clogged fuel filter. Technician B says that the IAC valve may be stuck in the fully extended position. 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 BWhile a clogged fuel filter could certainly create a hard or no start complaint, throttle position would have no effect on easing the condition so Technician B is incorrect. An IAC valve regulates idle speed by directing air around the closed throttle plate. With the valve fully extended, there is no air bypass. This is the minimum idle position. As the ECM commands a higher idle speed, the IAC valve retracts to open up the air bypass channel. In most cases, an MFI engine will start and run at minimum idle, as long as the throttle body is clean and the idle stop screw is adjusted correctly allowing the minimum airflow. The information in the question provides an important clue to technician B’s answer. The vehicle had only received an occasional oil change in 80,000 miles. This is reason to suspect that the throttle body was heavily coated with crankcase contaminants. If the IAC valve was stuck in the fully extended position then the engine would not start unless the throttle was held open, therefore Technician B is correct.

14. The composite vehicle lacks power. The engine has been recently tuned-up and the results from the power balance test were good. The following snap-shot of scan data was taken at 2500rpm no load. Which analysis of this information is correct? Technician A says that the problem could be the result of low fuel pressure. Technician B says that root cause of the problem may caused by a plugged catalytic converter. Who is correct?
A. Technician A only
B. Technician B only
C. Both Technicians
D. Neither Technicians
The correct answer is B The answer to this diagnosis can be found in the MAP, H02S and fuel trim readings. Given the high-rpm, no-load conditions under which the snapshot was taken, the MAP reading should be closer to 1.5 volts rather than the indicated value of 3.6V. This high MAP reading shows that manifold pressure is above normal, which is consistent with a clogged converter. A restricted converter causes combustion gases to accumulate inside the cylinders. During the overlap period, in which the intake and exhaust valves are open briefly, the excess gas leaks into the intake manifold. This creates positive pressure and reduces vacuum, in the same way a leaking EGR valve does at dosed throttle. Because the accumulated gas dilutes the incoming air/fuel charge, there is less oxygen detected by the 02 sensors. This is why the upstream H02S readings are high and the fuel trim readings are low. Incidentally, the negative fuel trim response indicates that the ECM is attempting to compensate for what it believes is a rich mixture. As you can see, technician .PI.s suggestion is correct. Although low fuel pressure is a potential cause of poor driveability, in this case a lack of power, the scan data does not support this diagnosis. If fuel pressure were low, as technician A stated, the engine would have a lean condition. The H02S and fuel trim readings would reflect this by having low O2 sensor voltage and a positive fuel trim reading (adding fuel).

15. Two technicians are discussing the effect air injection has on the CO2 (carbon dioxide) and O2 (oxygen) readings from a properly functioning vehicle. Technician A says that disabling the air injection system will cause an increase in the 02 reading. Technician B says that C02 reaches its highest point with the air injection system enabled. 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 With the air injection system disabled, the only oxygen in the exhaust is the trace amount unused by the converter. Oxygen levels are always higher when air injection is active, therefore Technician A’s answer is incorrect. Technician B’s answer is also incorrect. Carbon dioxide will be at its lowest point (not highest) when the air injection system is operating due to the fact that air injection dilutes the C02 sample. Remember that carbon dioxide is an indicator of combustion efficiency, while oxygen is useful for evaluating the catalytic converter performance and identifying a lean air/fuel ratio.

16. A customer complains that their vehicle lacks power. What should be the first step in determining the cause of the problem?
A. Analyze scan data
B. Test drive the vehicle
C. Measure fuel pressure
D. Check exhaust backpressure
The correct answer is B The first step in solving a performance problem is to confirm that an abnormal condition actually exists. That’s why a road test should always precede any diagnostic procedures, such as those mentioned in the list of responses. In some cases, a driveability complaint may turn out to be nothing more than a customer’s unrealistic expectation of their vehicle’s performance capabilities. A test drive will allow you to verify the problem actually exists, and then determine the appropriate course of action from there.

17. The torque converter clutch on the composite vehicle will not engage. Technician A says a short to ground at pin 72 of the TCM may be the cause. Technician B says that a voltage short to pin 64 of the ECM may 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 TCM turns on the torque converter clutch by a ground signal at pin 72. If this connection was shorted to ground, the TCC would remain engaged, so technician A is incorrect. When the brake pedal pressure sensor sends a voltage input to pin 64 of the ECM, the TCM disengages the torque converter dutch. If this wire was shorted to a source of voltage, the input to the ECM would be the same as hitting the brake pedal, and the TCC would not engage. Technician B is therefore correct.

18. All of the following could cause an engine with an waste spark ignition to misfire EXCEPT:
A. Low primary circuit resistance
B. Open plug wire
C. Defective ignition coil module
D. Faulty generator
The correct answer is A In order for a coil to generate sufficient secondary voltage, the primary circuit must provide a low-resistance path for current to flow. Only if the primary circuit had high resistance would it cause a misfire. This is why response A is the right answer. The most common cause of a misfiring cylinder is an open spark plug wire. This is as true for waste spark systems as it is for engines using a distributor. Under this condition, the demand for secondary voltage exceeds the supply. As a result, combustion cannot occur. Low cha;rging system voltage can also cause an engine to misfire, especially under load. This is because the less voltage available to the primary coil winding, the less secondary energy will be produced. Obviously, this would be the case if the generator were undercharging, just as it would if there was high resistance (excessive voltage drop) in the primary circuit. In most waste spark systems, each coil’s primary winding is switched on and off through transistors in the ignition control module. Although the ECM determines timing and dwell, the module serves as the actuator. Consequently, a defective module could prevent one or more coils from working. In a waste spark system, this would result in at least two misfiring cylinders.

19. Idle speed is too high on an engine with a speed density fuel injection system. Technician A states that a leaking throttle body gasket may be causing the problem. Technician B says that someone may have replaced the PCV valve with the wrong type. 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 Both technician answers are correct. First of all in a speed density system, the ECM calculates engine airflow based on changes in the MAP sensor (manifold absolute pressure). The MAP sensor is designed to detect these changes. Under normal conditions, MAP output will be approximately 1-1.5 volts at closed throttle (low vacuum or manifold pressure), and rise to nearly 5 volts at wide-open throttle (high vacuum or manifold pressure). When an air leak exists, it causes manifold pressure to increase. As a result, the closed-throttle MAP output will be higher than normal. Since the ECM has no way of identifying the airflow source, it simply increases injector pulse width whenever it sees an increase in MAP. That’s why a high idle is a common problem on vehicles with speed density systems. The spring inside a PCV valve is calibrated for a specific flow rate. If the wrong valve is used, the engine can draw in excessive air. Although this type of air leak is not visually identifiable, like a cracked vacuum hose for example, the result is the same. The engine idles too high due to the increase in manifold pressure. The same is true for a leaking throttle body gasket, since it causes the engine to draw in additional air.

20. All of the following statements regarding the wiring diagram shown above are true EXCEPT:
A. A blown 20A fuse would result in 0 volts at ECM terminal 23.
B. The solenoid coil receives battery power at KOEO and KOER
C. The EGR valve is shown in the de-energized state.
D. The pintle position sensor is shown at approximately the 2.5V position.
The correct answer is A A Linear EGR Valve is controlled directly by the ECM. As a result, no vacuum signal is required for valve operation. As the wiring diagram shows, fused battery power is supplied to the EGR solenoid coil under Key On Engine Off (KOEO) and Key On Engine Run (KOER) conditions. This is why response B is a true. Response C is also true, since the ECM operates the valve through a ground driver shown in the de-energized position. The pintle position sensor is a potentiometer that operates off a 5-volt reference signal from terminal 42 of the ECM. The ECM monitors the feedback from this sensor to maintain precise control of EGR flow. In the wiring diagram, the sensor’s wiper arm is shown centered on the resistor strip, which would result in the ECM seeing about 2.5 volts at terminal 23, therefore response D is another true statement. If the 20A fuse were blown, the EGR valve would not operate. Under this condition, pintle position voltage would remain at one volt, which is the normal input signal at O% EGR (valve closed). This is why response A is the false statement.

21. The default throttle position on the composite vehicle is:
A. 0%
B. 15%
C. 20%
D. 30%
The correct answer is B The throttle actuator is operated in response to inputs from the Accelerator Pedal Position Sensors, and throttle position is monitored by two Throttle Position Sensors. If two or more sensors should fail, the TAC will be disabled, and the throttle will return to the spring loaded 15% position. This is the default position of the throttle on the composite vehicle. At 15% the engine will be in fast idle and limp in mode.

22. The CAN harness resistance on the composite vehicle is measured at 120 Ohms. Technician A says that a terminating resistor is open. Technician B says this is a normal resistance value. 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 CAN harness on the composite vehicle uses two 120 Ohm terminating resistors, which are integral to the instrument cluster and the ECM. When both resistors are intact harness resistance will be 60 Ohms. Technician A is correct and the harness resistance reading of 120 Ohms indicates an open terminating resistor.

23. The composite vehicle has an inoperable A/C clutch. Technician A says this condition could be due to a refrigerant leak. Technician B says an open circuit to ECM pin 27 could be 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 Cthe A/C pressure sensor would detect the low pressure condition caused by a refrigerant leak, and would send an input to the ECM to prevent clutch engagement. The A/C clutch is engaged when the ECM sends a low voltage signal & from pin 27. An open circuit here would also disable the A/C clutch.

24. There is poor engine performance on the composite vehicle. Technician A says a faulty exhaust cam position solenoid could be the cause. Technician B says a faulty intake cam position solenoid could be 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 B Exhaust valve timing on the composite vehicle is fixed and there is no exhaust cam position solenoid, therefore Technician A is incorrect. The composite vehicle does use intake cam position solenoids, which allow the ECM to constantly vary intake valve timing, therefore Technician B is correct.

25. Technician A says the MAF sensor is located on the intake manifold, and informs the ECM of intake manifold pressure. Technician B says the MAF sensor senses air volume in the air tube. It’s signal indicates engine load to the ECM. 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 A Manifold Absolute Pressure Sensor or MAP sensor senses the pressure in the intake manifold, indicating engine load, therefore technician A is incorrect. The Mass Air Flow Sensor or MAF sensor senses air volume in the air tube to indicate engine load. These are two different sensors, both used to inform the ECM of engine load.

This post was written by: Martin Hand

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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.