A-8 Engine Performance Q&A

1. An EGR valve vacuum solenoid has 18 Hg. as its vacuum source. The resistance checks out OK. Vacuum pressure is manually applied to the valve with a pump and a slight stumble is noticed. There is little drop in RPM. The most-likely cause of this is:
A a faulty vacuum solenoid.
B a poor vacuum source.
C a restriction in the EGR passage.
D a faulty EGR position sensor.
Answer C is correct. Always make sure the passages are open and not clogged before replacing an exhaust gas recirculating valve. If it’s clogged with carbon, use a small wire brush to clean out the passage.
 
 
2. A cylinder power balance test is being performed on a vehicle with sequential fuel injection. Two adjacent cylinders are under performing. Technician A says this could be due to a restriction in the fuel injectors. Technician B says this could be due to leaking secondary insulation. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. Both restricted fuel injectors and leaking secondary wires will reduce the cylinders contribution. It’s important to keep the wiring separated and in the proper clips to prevent leaking insulation and cross fire. A faulty head gasket will leak between two adjacent cylinders resulting in this condition.
 
 
3. A COP ignition system has no spark coming from any of the coils. Which of these is most likely the cause?
A A faulty PCM driver.
B Excess resistance in the primary circuit.
C Excess resistance in the secondary circuit.
D No power to PCM BAT+.
Answer D is correct. No power to, or a faulty PCM will result in no power to any of the coils and a no spark condition. With a coil on plug COP system, a faulty crankshaft position sensor can also cause a no spark condition for all of the cylinders.
 
 
4. 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
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer B is correct. 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. The ECM uses this signal to adjust fuel trim.
 
 
5. Technician A says a throttle position sensor is considered a potentiometer. Technician B says this sensor can be tested with an ohmmeter. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. Both Technicians are correct.
 
 
6. After performing a wet cylinder compression test, all of the cylinders remain low. Technician A says this may be incorrect camshaft timing. Technician B says this may be worn piston rings. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer A is correct. Technician A is correct. Incorrect camshaft timing results in low compression.
 
 
7. A vacuum gauge is connected to the intake manifold of an engine. The needle fluctuates between (15 and 20 in Hg) at idle. This reading indicates:
A A normal condition.
B Late ignition or valve timing.
C A burned exhaust valve.
D A restricted exhaust.
Answer C is correct. If the gauge readings fluctuate between (15 and 20 in Hg), this indicates a stuck valve or a misfire.
 
 
8. Technician A says a stuck closed EGR (exhaust gas recirculating) valve will cause an engine to stumble or stall. Technician B says a stuck open EGR valve will cause detonation. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer D is correct. Neither technician is correct.
 
 
9. At idle, a vehicle is emitting black smoke from its tailpipe. The most likely cause of this condition is:
A A leaking fuel injector.
B Worn piston rings.
C A blown head gasket.
D Leaking valve seals.
Answer A is correct. A leaking fuel injector causes a rich fuel mixture. A rich fuel condition causes black colored smoke to emit from the tailpipe. (Fuel)
 
 
10. A vehicle has a lack of power while accelerating. A vacuum gauge reads 10Hg at 2500 RPM. The most-likely cause of this reading is:
A Burned exhaust valve.
B Late valve timing.
C A faulty head gasket.
D A clogged catalytic converter.
Answer D is correct. If the needle drops steady during acceleration there’s a restriction in the exhaust. This is reading is most likely caused by a clogged catalytic converter.
 
 
11. Which of these is least-likely to cause a rich fuel condition:
A A leaking fuel injector.
B A faulty fuel pressure regulator.
C A faulty ECT engine coolant temperature sensor.
D A stuck closed thermostat.
Answer D is correct. A stuck closed thermostat will cause a vehicle to overheat. A thermostat that’s stuck open delays or prevents the engine from reaching its optimum operating temperature, causing a rich fuel condition.
 
 
12. Technician A says a heater circuit in an oxygen sensor brings the sensor to operating temperature. Technician B says the engine control module uses the oxygen sensor’s voltage signal to adjust fuel trim in closed loop. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. An oxygen sensors heater circuit is designed to bring the sensor to operating temperature and closed loop quickly. It sends a voltage signal to the engine control module in closed loop.
 
 
13. Two technicians are discussing a turbocharged engine. Technician A says the wastegate is a component used to control boost pressure. Technician B says when opened, the wastegate diverts exhaust gas from the turbine wheel. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. Both technicians are correct.
 
 
14. An emission test is performed on a six cylinder engine. The test indicates high levels of NOx. The most likely cause of this condition is:
A a rich air fuel mixture.
B a clogged catalytic converter.
C a cylinder misfire.
D a stuck closed EGR valve.
Answer D is correct. A stuck closed EGR valve will result in high cylinder temperatures and high NOx in the emissions.
 
 
15. Two technicians are discussing a voltage drop test. Technician A says to perform a voltage drop test if a corroded ground connection is suspected. Technician B says to perform a voltage drop test if excessive resistance is suspected. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. Both technicians are correct.
 
 
16. Technician A says a stuck open PCV valve will cause a lean fuel condition. Technician B says the PCV system removes blowby gases from the crankcase. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. Both technicians are correct.
 
 
17. Technician A says the crankshaft position sensor monitors crankshafts speed and rotation. Technician B says a permanent magnet crankshaft position sensor always has three wires. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer A is correct. The crankshaft position sensor monitors crankshafts speed and rotation.
 
 
18. Technician A says a defective evaporative purge valve may cause a rich air fuel ratio. Technician B says an evaporative pressure sensor is used to notify the PCM of gas tank pressure. Who is correct?
A Technician A
B Technician B
C Both Technician A and B
D Neither Technician A or B
Answer C is correct. Both technicians are correct.
 
 
19. A cylinder power balance test is being performed on a four cylinder engine. A spark plug wire is removed from its corresponding spark plug and a slight drop in RPM is noticed.
A This is normal.
B A significant drop should be indicated.
C There should be no drop at all.
D There is no such thing as an engine cylinder power balance test.
Answer B is correct. A significant drop in RPM should be noticed.
 
 
20. A cylinder compression test is performed on an eight cylinder engine. These results most likely indicate:
A burned exhaust valves.
B weak piston rings.
C a faulty head gasket.
D retarded valve timing.
Answer C is correct. When there are low compression pressures in adjacent cylinders the head gasket is probably leaking compression between the two.
 
 
21. Technician A says the PCM will advance ignition timing when it receives a voltage signal from the knock sensor. Technician B says this sensor sends an AC signal to the PCM when it detects ping or spark knock. Who is correct?
A. Technician A
B. Technician B
C. Both Technician A and B
D. Neither Technician A or B
Answer B is correct. The knock sensor creates and sends an AC voltage signal whenever engine knock is present to the ECM/PCM.
 
 
22. There’s a misfire at the #3 cylinder of a COP ignition system. There is no power at the Bat+ terminal of the coil. Which of these is most-likely the cause?
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 the PCM.
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 PCM and the coil would result in no spark at the cylinder.
 
 
23. An enhanced EVAP system has a code indicating a gross leak detected. Which of the following is
most likely the cause?
A. A crimp in the vent hose.
B. A saturated canister.
C. A stuck closed purge valve.
D. A loose fuel filler cap.
Answer D is correct. A loose fuel filler cap will result in a gross leak detected code and is actually the most common fault found in the enhanced EVAP system. People leave the caps loose after filling. Some systems illuminate a unique loose gas cap light on the instrument panel whenever this code is detected.
 
 
24. A catalytic converter is damaged from heat. Technician A says this damage is most likely caused by cylinder misfiring. Technician B says this is most likely caused by low fuel volume. Who is correct?
A. Technician A
B. Technician B
C. Both Technician A and B
D. Neither Technician A or B
Answer A is correct. A misfiring engine causes a high concentration of hydrocarbons in the exhaust. A rich fuel mixture or misfiring engine will result in excess unburned fuel (HC’s) to enter the catalytic converter resulting in converter overheating.
 
 
25. A vehicle has a fuel trim of +5 at idle and +25 at cruise. The vehicle has a steady oxygen sensor reading of 800Mv. When the vacuum hose is disconnected from the brake booster check valve there is no change in the oxygen sensors reading. The most likely cause for this reading is:
A. An intake manifold leak.
B. A faulty throttle position sensor.
C. A faulty oxygen sensor.
D. A kink in the fuel return line.
Answer C is correct. A faulty or stuck oxygen sensor may result in a rich fuel condition, and would not change it’s output when a vacuum hose is removed. Removing a vacuum hose while monitoring the sensor is a way to see if the sensor signal varies.

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.