Step2Study

Automotive Service Excellence (ASE) A8 Engine Performance practice questions

230 free questions with answers and explanations.

Practice test
  1. 201.A technician is diagnosing a vehicle with an intermittent misfire that primarily occurs during hard acceleration. They connect an oscilloscope to the secondary ignition system and observe a waveform with a very short spark line (ignition duration) and a high firing voltage (kV). Which of the following is the MOST likely cause?Ignition System Diagnosis and Repair
  2. 202.A technician is diagnosing a vehicle with a complaint of significant power loss, especially noticeable during acceleration, and poor fuel economy. A vacuum gauge connected to the intake manifold shows a reading that drops to near zero during acceleration and then slowly recovers, but never reaches a steady, high reading. What is the most likely cause?General Engine Diagnosis
  3. 203.A technician is performing an engine compression test on a vehicle that exhibits a significant loss of power and rough running. The dry compression test results for all cylinders are between 70-80 psi. What is the most likely cause?General Engine Diagnosis
  4. 204.A technician is diagnosing a vehicle with a persistent P0301 (Cylinder 1 Misfire) code. They have confirmed spark and fuel delivery to cylinder 1. The next step is to check for proper compression. A compression test on cylinder 1 yields a reading of 80 PSI, while the other cylinders are consistently at 150 PSI. What is the MOST likely cause of the P0301 code in this scenario?Ignition System Diagnosis and Repair
  5. 205.A client complains that their vehicle experiences a rough idle and occasional stalling, especially when the engine is cold. A technician performs a visual inspection and finds no obvious issues. Using a scan tool, they observe that the engine control module (ECM) is consistently commanding a low ignition advance at idle. Which sensor input is MOST likely causing the ECM to retard timing in this scenario?Ignition System Diagnosis and Repair
  6. 206.A technician is diagnosing an engine with a complaint of a consistent, rhythmic 'knocking' sound that is most noticeable when the engine is cold or under light load, and tends to decrease as the engine warms up. The noise sounds somewhat like a piston hitting the cylinder wall. Which of the following is the most likely cause?General Engine Diagnosis
  7. 207.A vehicle with an Air Injection Reaction (AIR) system is diagnosed with a 'Check Engine' light and a DTC P0410, 'Secondary Air Injection System Malfunction'. The technician observes that the AIR pump runs continuously after engine start-up, even when the engine is warm. What is the MOST likely cause of this continuous operation?Emissions Control Systems Diagnosis and Repair
  8. 208.A diesel vehicle equipped with a Selective Catalytic Reduction (SCR) system is brought in with a complaint of reduced engine power and a 'check engine' light illuminated. The scan tool reveals a P20EE (SCR NOx Catalyst Efficiency Below Threshold Bank 1) DTC. The Diesel Exhaust Fluid (DEF) level is full, and the DEF quality sensor shows normal readings. Which of the following is the MOST likely cause?Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair
  9. 209.A client reports that their vehicle's engine exhibits a dull, heavy 'thud' or 'rumble' noise that is most pronounced at idle and under load, and its frequency directly correlates with engine RPM. This noise is typically heard from the lower part of the engine. Which of the following is the most likely cause?General Engine Diagnosis
  10. 210.A vehicle is brought to a shop with a complaint of a strong sulfur or 'rotten egg' smell from the exhaust, especially under heavy acceleration. The 'Check Engine' light is not illuminated, and there are no stored DTCs. Which of the following is the MOST likely cause of this odor?Emissions Control Systems Diagnosis and Repair
  11. 211.A technician is diagnosing an intermittent misfire on a vehicle with a Coil-On-Plug (COP) ignition system. The misfire only occurs after the engine has reached operating temperature and has been running for an extended period. When the engine cools down, the misfire disappears. Which of the following components is MOST likely failing due to thermal breakdown?Ignition System Diagnosis and Repair
  12. 212.A technician is performing an engine condition diagnosis on a vehicle with a complaint of a rough idle and a noticeable loss of power. The vacuum gauge reading is consistently low, around 10-12 in. Hg, and the needle shows a rapid, rhythmic fluctuation between 2-4 in. Hg. What is the most likely cause?General Engine Diagnosis
  13. 213.A technician is performing a comprehensive inspection of an older vehicle's distributor-type ignition system. They notice significant corrosion and carbon tracking on the inside of the distributor cap and on the rotor tip. What is the MOST immediate consequence of this condition on the ignition system's performance?Ignition System Diagnosis and Repair
  14. 214.A vehicle owner complains of a noticeable increase in fuel consumption and a slight loss of power, but the engine runs smoothly and has no obvious noises or vibrations. A dry compression test yields readings of 160 psi, 165 psi, 158 psi, and 162 psi for cylinders 1 through 4, respectively. What is the most likely conclusion based on these compression readings?General Engine Diagnosis
  15. 215.A technician is diagnosing an engine that occasionally stalls at idle and has a consistent, rhythmic 'thumping' noise that is most pronounced at idle and under light load. The noise seems to originate from the lower part of the engine and its frequency is roughly half the engine's RPM. What is the most likely cause?General Engine Diagnosis
  16. 216.A technician is performing an exhaust gas analysis on a vehicle. The readings show consistently high levels of hydrocarbons (HC) and carbon monoxide (CO), with low oxygen (O2) levels. The catalytic converter is at operating temperature. What does this indicate about the engine's air-fuel mixture?Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair
  17. 217.A technician observes a vacuum gauge reading that is consistently low, around 10-12 in. Hg, but the needle is steady and does not fluctuate. The engine has reduced power and poor fuel economy. What is the most likely cause?General Engine Diagnosis
  18. 218.A technician is performing a diagnosis on a vehicle that intermittently runs rough, especially under load, and has a P0301 DTC (Cylinder 1 Misfire Detected). The technician has already checked spark, fuel pressure, and injector pulse. The next step is to perform a cylinder power balance test. During the test, when Cylinder 1's injector is disabled, there is no change in engine RPM. When Cylinder 2's injector is disabled, the engine RPM drops significantly. What does this indicate for Cylinder 1?Computerized Engine Controls Diagnosis and Repair
  19. 219.A technician is diagnosing a vehicle with a complaint of intermittent stalling and difficult starting, especially when the engine is warm. The scan tool shows no active Diagnostic Trouble Codes (DTCs). During cranking, the technician observes a very low or erratic engine RPM reading on the scan tool, even though the engine is clearly turning over. What sensor is most likely at fault?Computerized Engine Controls Diagnosis and Repair
  20. 220.A technician is diagnosing a vehicle with a complaint of a rough idle and occasional stalling. Using a scan tool, the technician observes that the Idle Air Control (IAC) valve duty cycle is consistently at 0% when the engine is idling, and the engine struggles to maintain RPM. There are no active DTCs. What is the most likely cause?Computerized Engine Controls Diagnosis and Repair
  21. 221.A technician is diagnosing a vehicle with a complaint of poor fuel economy and a Check Engine Light (CEL) illuminated. Using a scan tool, the technician observes a consistently high short-term fuel trim (STFT) and long-term fuel trim (LTFT) values, both above +20%. The upstream oxygen (O2) sensor voltage fluctuates between 0.1V and 0.9V, but the downstream O2 sensor voltage is consistently around 0.7V. Which of the following is the most likely cause?Computerized Engine Controls Diagnosis and Repair
  22. 222.A client complains that their vehicle experiences a noticeable loss of power under acceleration and the engine feels 'sluggish.' Using a scan tool, a technician observes that the Manifold Absolute Pressure (MAP) sensor reading at wide-open throttle (WOT) is only 15 in.Hg, while the specification for this engine at WOT is typically close to atmospheric pressure (around 28-30 in.Hg at sea level). What is the most likely cause of this discrepancy?Computerized Engine Controls Diagnosis and Repair
  23. 223.A technician is diagnosing a vehicle with a complaint of poor acceleration and black smoke from the exhaust, especially under load. The scan tool shows a Mass Air Flow (MAF) sensor reading of 5 grams/second (g/s) at idle and 50 g/s at wide-open throttle (WOT). The engine specification for this 3.0L V6 engine typically calls for approximately 3-5 g/s at idle and around 120-150 g/s at WOT. Which of the following is the most likely cause?Computerized Engine Controls Diagnosis and Repair
  24. 224.A technician is diagnosing a vehicle with a complaint of poor fuel economy and a strong smell of raw fuel from the exhaust. The scan tool shows that the upstream oxygen (O2) sensor voltage is consistently high (around 0.8V - 0.9V) and both short-term fuel trim (STFT) and long-term fuel trim (LTFT) are very low negative (-20% to -25%). What is the most likely cause?Computerized Engine Controls Diagnosis and Repair
  25. 225.A technician is diagnosing a vehicle with a complaint of a rough idle and a P0300 DTC (Random/Multiple Cylinder Misfire Detected). The scan tool shows misfires on cylinders 2 and 4. Further investigation reveals that Cylinders 2 and 4 are on the same ignition coil secondary circuit (waste spark system). What is the most likely cause of this specific misfire pattern?Computerized Engine Controls Diagnosis and Repair
  26. 226.A technician is performing a pre-purchase inspection on a used vehicle. The Check Engine Light (CEL) is off, but when checking emission monitor status with a scan tool, the technician finds that the 'Catalyst Monitor' and 'EVAP System Monitor' are 'Not Ready'. All other monitors are 'Complete'. The vehicle has recently had its battery replaced. What is the most likely reason for the 'Not Ready' status of these specific monitors?Computerized Engine Controls Diagnosis and Repair
  27. 227.A technician is diagnosing a vehicle with a complaint of a rough idle and occasional stalling when the engine is warm. The scan tool shows no active DTCs, but the short-term fuel trim (STFT) fluctuates wildly between -15% and +15% at idle. When the engine is revved to 2500 RPM, the STFT stabilizes around 0%. Which of the following is the most likely cause?Computerized Engine Controls Diagnosis and Repair
  28. 228.A technician is diagnosing a vehicle that exhibits a sudden loss of engine power, accompanied by a 'check engine' light and a P0203 DTC (Injector Circuit / Open - Cylinder 3). After inspecting the wiring harness and connectors for Cylinder 3 injector and finding no obvious damage, what is the next logical step in diagnosis?Computerized Engine Controls Diagnosis and Repair
  29. 229.A technician is diagnosing a vehicle with a complaint of extended cranking times, especially after sitting for several hours. Once started, the engine runs normally, and there are no active DTCs. The technician connects a fuel pressure gauge and observes that the fuel pressure drops rapidly from 55 psi to 10 psi within 5 minutes after the engine is shut off. What is the most likely cause of this issue?Computerized Engine Controls Diagnosis and Repair
  30. 230.A technician is performing a diagnostic on a vehicle with a Check Engine Light (CEL) and a P0171 DTC (System Too Lean, Bank 1). The scan tool shows that the upstream oxygen (O2) sensor voltage is consistently low (around 0.1V - 0.2V), and both short-term fuel trim (STFT) and long-term fuel trim (LTFT) for Bank 1 are very high positive (+25% to +30%). After checking for vacuum leaks and finding none, the technician suspects a fuel delivery issue. What is the next logical step in diagnosis?Computerized Engine Controls Diagnosis and Repair