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Automotive Service Excellence (ASE) A8 Engine Performance practice questions

230 free questions with answers and explanations.

Practice test
  1. 101.A technician is performing a cylinder leakage test on cylinder #2. With the piston at Top Dead Center (TDC) on the compression stroke, 100 psi of shop air is applied to the cylinder. Air is heard escaping from the oil filler cap. What does this indicate?General Engine Diagnosis
  2. 102.A technician is performing an ignition system inspection. They notice that the coil-on-plug (COP) boots on several cylinders show signs of arc tracking (small burn marks or lines). The customer reports occasional misfires during hard acceleration. What is the MOST effective repair strategy for this issue?Ignition System Diagnosis and Repair
  3. 103.A technician is diagnosing an intermittent misfire on a vehicle with a Waste Spark ignition system. The misfire predominantly occurs on cylinder #1 and cylinder #4. During testing, the technician measures the spark plug resistance for both cylinders and finds that cylinder #1 has significantly higher resistance than cylinder #4. What is the MOST likely implication of this finding in a waste spark system?Ignition System Diagnosis and Repair
  4. 104.A client reports that their vehicle's engine runs roughly and has significantly reduced power. A technician performs a cylinder leakage test on cylinder #2. With the piston at Top Dead Center (TDC) on the compression stroke, 100 psi of shop air is applied. The gauge on the leakage tester shows 40% leakage, and a distinct 'hissing' sound is heard from the oil filler cap. What does this indicate?General Engine Diagnosis
  5. 105.A technician is using an oscilloscope to diagnose an intermittent misfire on a vehicle with a Coil-On-Plug (COP) ignition system. They observe that the secondary ignition waveform for cylinder #3 occasionally displays a very short spark line duration, often followed by an immediate 'coil oscillation' without a proper spark event, while other cylinders show normal waveforms. What is the most likely cause of this specific waveform pattern?Ignition System Diagnosis and Repair
  6. 106.A vehicle owner reports a continuous, light 'hissing' sound coming from the engine's intake manifold area, accompanied by a slightly elevated and unstable idle. The check engine light is on, indicating a 'System Too Lean' condition. What is the most likely cause?General Engine Diagnosis
  7. 107.A technician is performing a voltage drop test on the primary side of an ignition coil. With the ignition key ON and engine OFF, the technician measures 12.5V at the coil's positive terminal relative to ground. When the engine is cranking, the voltage drops to 10.0V. The specification for cranking voltage at the coil is typically no less than 9.5V. What does this voltage drop indicate?Ignition System Diagnosis and Repair
  8. 108.A technician is inspecting the ignition system of a distributor-equipped vehicle experiencing a rough idle. They find that the distributor cap terminals are heavily corroded. What effect would this corrosion MOST likely have on the ignition system's performance?Ignition System Diagnosis and Repair
  9. 109.A vehicle exhibits a severe, rhythmic 'thump' or 'clunk' noise that is directly proportional to engine RPM, present at all times, and sounds like it's coming from deep within the engine block. The noise does not change significantly with engine load or temperature. What is the MOST likely cause?General Engine Diagnosis
  10. 110.A technician is performing an engine compression test on a vehicle with a complaint of reduced power and rough idle. The dry compression readings for cylinders 1-4 are 145 psi, 150 psi, 100 psi, and 148 psi, respectively. What is the MOST likely cause for the reading on cylinder #3?General Engine Diagnosis
  11. 111.A technician is performing a diagnostic check on a vehicle experiencing a no-start condition. Using a spark tester, they confirm that there is no spark from any of the ignition coils. A scan tool shows no communication with the Engine Control Module (ECM). All fuses related to the ECM and ignition system are checked and found to be good. What should the technician check NEXT to diagnose the no-start condition?Ignition System Diagnosis and Repair
  12. 112.A technician is diagnosing an engine that exhibits a severe, rhythmic 'thump' or 'clunk' noise that is directly proportional to engine RPM and becomes louder under load. The noise is present at all engine speeds but is most concerning when accelerating. A cylinder cut-out test reveals that disabling cylinder #3 significantly reduces the noise. What is the most likely cause?General Engine Diagnosis
  13. 113.A technician is diagnosing a vehicle with a P0351 trouble code (Ignition Coil 'A' Primary/Secondary Circuit Malfunction). Using an oscilloscope, they observe a normal primary ignition waveform but no corresponding secondary ignition waveform. What is the most likely cause of this issue?Ignition System Diagnosis and Repair
  14. 114.A technician is using an oscilloscope to analyze the secondary ignition waveform of a cylinder. The waveform shows a very short spark line duration (arc duration) and a high firing voltage (kV). All other cylinders show normal spark line duration and firing voltage. What does this specific waveform characteristic MOST likely indicate?Ignition System Diagnosis and Repair
  15. 115.A client complains of a rough idle and occasional stalling on their vehicle. A technician connects a scan tool and finds no diagnostic trouble codes (DTCs). Further investigation reveals that the engine intermittently runs lean. When checking the ignition system, the technician measures the primary ignition coil resistance and finds it to be significantly higher than specifications. What effect would this high primary resistance MOST likely have on the ignition system?Ignition System Diagnosis and Repair
  16. 116.A technician is diagnosing a vehicle with a persistent P0352 (Ignition Coil 'B' Primary/Secondary Circuit Malfunction) trouble code. They have already confirmed power and ground to the coil, and swapped the coil with an adjacent cylinder, but the code remains for cylinder #2. Using an oscilloscope on the control circuit wire for cylinder #2's coil, they observe a constant 12-volt signal with no switching activity from the ECM. What is the most likely cause of this symptom?Ignition System Diagnosis and Repair
  17. 117.A technician is investigating a vehicle that stalls intermittently and has difficulty restarting when hot. The primary ignition coil resistance measures within specifications when cold, but after the engine stalls, the resistance is found to be significantly higher than specified. What is the most likely cause of this issue?Ignition System Diagnosis and Repair
  18. 118.A vehicle owner reports a significant drop in fuel economy and a noticeable loss of power, but no unusual noises or visible smoke. A technician performs a cylinder power balance test. When cylinder #4 is momentarily disabled, there is a significant drop in engine RPM, similar to when any other cylinder is disabled. What does this power balance test result indicate for cylinder #4?General Engine Diagnosis
  19. 119.A technician observes an engine that has a slight, consistent vibration at idle. Using a stethoscope, the technician isolates the noise to the area of the accessory drive belt tensioner. The vibration does not significantly change with engine RPM, and no specific misfire is detected. What is the most likely cause?General Engine Diagnosis
  20. 120.A vehicle owner reports a significant loss of power, especially noticeable during acceleration, and poor fuel economy. The engine starts and idles smoothly, and there are no abnormal noises or smoke from the exhaust. A vacuum gauge test shows a normal idle reading, but when revved, the needle drops and then slowly, sluggishly returns to the idle reading. What is the MOST likely cause?General Engine Diagnosis
  21. 121.A technician is performing an engine condition diagnosis on a vehicle with a complaint of significant power loss and a 'chugging' sensation under acceleration. Using a vacuum gauge, the technician observes a reading that is initially normal at idle, but drops significantly and fluctuates erratically under acceleration. What does this vacuum gauge reading most likely indicate?General Engine Diagnosis
  22. 122.A client complains that their vehicle intermittently stalls and has a 'check engine' light illuminated. A technician retrieves diagnostic trouble code P0340, indicating a Camshaft Position Sensor (CMP) Circuit Malfunction. Which of the following is the MOST likely impact of a failing CMP sensor on the ignition system?Ignition System Diagnosis and Repair
  23. 123.A technician performs a wet compression test on cylinder #3 of an engine that had a dry reading of 80 psi (specification 150 psi). After adding a small amount of oil, the compression reading for cylinder #3 increases to 130 psi. What does this result primarily indicate?General Engine Diagnosis
  24. 124.A technician is diagnosing a vehicle with an intermittent misfire on cylinder #2. The misfire is more pronounced during humid weather. After inspecting the spark plug and coil, which appear normal, the technician decides to perform a leakage test. Which of the following tools or methods would be most effective for detecting high voltage leakage in the ignition system under these conditions?Ignition System Diagnosis and Repair
  25. 125.A technician is diagnosing an engine with a complaint of excessive oil consumption (approximately 1 quart per 750 miles) but no visible external leaks. The exhaust produces a noticeable blue-gray smoke during acceleration after idling for a period. What is the most likely cause of this oil consumption?General Engine Diagnosis
  26. 126.A technician is performing a comprehensive diagnostic on a vehicle with a persistent P0301 (Cylinder 1 Misfire) code. After verifying fuel and compression are good, they connect an oscilloscope to observe the secondary ignition waveform for cylinder #1. They notice that the spark line is very short in duration and has a very high firing voltage (kV). What does this waveform characteristic most likely indicate?Ignition System Diagnosis and Repair
  27. 127.During a routine maintenance inspection, a technician notices that the spark plugs from a vehicle with 80,000 miles show signs of significant electrode erosion and a very wide gap. The vehicle owner reports no current driveability issues. What is the most appropriate action for the technician to take?Ignition System Diagnosis and Repair
  28. 128.A client reports that their vehicle's engine runs rough, has reduced power, and occasionally stalls. A technician performs a compression test, and all cylinders show readings around 90-100 psi, which is significantly lower than the manufacturer's specification of 150 psi. What is the most likely general cause?General Engine Diagnosis
  29. 129.A client reports that their vehicle experiences a noticeable, but not severe, vibration that seems to worsen slightly with engine RPM, but is present even at idle. The vibration can be felt through the steering wheel and floorboards. A visual inspection reveals no obvious issues with engine mounts or accessories. Which of the following is the MOST likely cause?General Engine Diagnosis
  30. 130.A technician is diagnosing a vehicle with a P0304 (Cylinder 4 Misfire) code. After performing a cylinder balance test, which confirms a misfire on cylinder 4, the technician removes the spark plug. The spark plug electrode is severely eroded, and the insulator is cracked. What is the most likely underlying cause of this spark plug condition?Ignition System Diagnosis and Repair
  31. 131.A technician is diagnosing an engine with a persistent misfire on cylinder #3. They perform a cylinder power balance test and observe a significant drop in RPM when cylinder #3's spark plug wire is momentarily disconnected, similar to other cylinders. What does this observation most likely indicate?General Engine Diagnosis
  32. 132.A client reports that their vehicle occasionally experiences a momentary loss of power and a 'stumble' under light to moderate acceleration. There are no stored DTCs. A technician suspects a transient ignition issue. Which of the following diagnostic tools or techniques would be most effective for capturing and identifying an intermittent ignition event that does not set a code?Ignition System Diagnosis and Repair
  33. 133.A technician is diagnosing a misfire on cylinder #3 of an engine equipped with a Coil-On-Plug (COP) ignition system. Using a scan tool, the technician observes a consistent misfire count on cylinder #3. Which of the following is the MOST appropriate next step in diagnosing the issue?Ignition System Diagnosis and Repair
  34. 134.A client complains of a loud, rhythmic 'tapping' or 'ticking' noise coming from the top of the engine, which increases in frequency with engine RPM. The noise is more pronounced when the engine is cold and tends to quiet down slightly as it warms up. What is the most probable cause?General Engine Diagnosis
  35. 135.During a routine inspection, a technician observes that the spark plugs on a vehicle are fouled with black, sooty deposits. The engine has been exhibiting symptoms of poor fuel economy and a rich running condition. Which of the following is the MOST likely cause for the spark plug fouling in this scenario?Ignition System Diagnosis and Repair
  36. 136.A vehicle owner reports a significant loss of power and poor fuel economy, especially under heavy acceleration. The technician uses a scan tool and finds no misfire codes, but observes that the ignition timing advance is consistently lower than commanded values at higher RPMs and loads. All ignition components (coils, plugs, wires) test good. What could be the MOST likely cause for the reduced ignition timing advance?Ignition System Diagnosis and Repair
  37. 137.A client reports a continuous, light 'hissing' sound coming from the engine's intake manifold area, especially noticeable at idle. The engine also idles rough and has reduced power. Which of the following is the MOST likely cause?General Engine Diagnosis
  38. 138.A technician observes a vacuum gauge reading that is steady at 21 in. Hg at idle. When the throttle is snapped open and then closed quickly, the needle drops to 2 in. Hg, then quickly rises to 28 in. Hg, before settling back to 21 in. Hg. What does this vacuum gauge reading indicate?General Engine Diagnosis
  39. 139.A technician is diagnosing an engine that exhibits a consistent, rhythmic 'knocking' sound that is loudest at idle and disappears or significantly diminishes as engine RPM increases. What is the most likely cause of this noise?General Engine Diagnosis
  40. 140.A technician observes a vacuum gauge reading that is consistently low (around 10-12 in. Hg) and fluctuates rapidly when the engine is at idle. What does this reading MOST likely indicate?General Engine Diagnosis
  41. 141.A technician is testing a Coil-On-Plug (COP) ignition system on a vehicle experiencing an intermittent misfire. They use a spark tester to check for spark at the affected cylinder. The spark tester shows a weak, yellowish spark. What is the most likely reason for a weak, yellowish spark instead of a strong, blue-white spark?Ignition System Diagnosis and Repair
  42. 142.A vehicle owner reports a significant loss of power, especially noticeable during acceleration, and the engine feels 'choked' or 'stifled'. There are no misfire codes, but fuel economy has decreased. A vacuum gauge test shows a normal reading at idle (19 in. Hg) but drops significantly and does not recover quickly when the throttle is opened quickly. What is the MOST likely cause?General Engine Diagnosis
  43. 143.A vehicle with a distributor-type ignition system is experiencing a no-start condition. The technician confirms that the ignition coil is receiving battery voltage on its primary positive terminal when the key is in the 'RUN' and 'START' positions. However, there is no spark at the spark plugs. What component should the technician investigate next to determine why the primary circuit is not being switched (grounded) to induce a spark?Ignition System Diagnosis and Repair
  44. 144.A technician observes a vacuum gauge reading that is consistently low (around 10-12 in. Hg) while the engine is idling. When the throttle is quickly opened and then closed, the needle drops slightly, then slowly rises to only about 15 in. Hg before returning to the low idle reading. What is the most probable cause of this vacuum gauge behavior?General Engine Diagnosis
  45. 145.A technician is performing a comprehensive inspection of a vehicle's ignition system. They notice significant white, powdery corrosion on the terminals inside the distributor cap and on the rotor tip. The vehicle owner reports occasional hesitation and misfires, especially in damp weather. What is the most likely impact of this corrosion on the ignition system's performance?Ignition System Diagnosis and Repair
  46. 146.A technician is performing an engine condition diagnosis on a vehicle with a complaint of a rough idle and occasional stalling. After verifying no obvious vacuum leaks or ignition issues, a vacuum gauge is connected. The gauge needle drops to virtually zero immediately after the engine is shut off. What does this indicate?General Engine Diagnosis
  47. 147.A vehicle owner reports a noticeable increase in fuel consumption and a slight loss of power, but no obvious misfires or smoke. A compression test reveals all cylinders are within specification (160-170 psi) and within 10% of each other. A cylinder leakage test shows less than 10% leakage on all cylinders. What is the next logical step in diagnosing the engine's condition?General Engine Diagnosis
  48. 148.A technician is diagnosing an engine with a P0303 trouble code (Cylinder 3 Misfire). After confirming the misfire is present, they perform a spark plug inspection. The spark plug from cylinder #3 appears to have a white, blistered insulator and eroded electrodes. What is the most likely cause of this spark plug condition?Ignition System Diagnosis and Repair
  49. 149.A technician is performing an engine condition diagnosis on a vehicle with a complaint of a rough idle and a slight loss of power, but no unusual noises. A vacuum gauge reading is steady at 17 in. Hg at idle. When the throttle is quickly opened and released, the needle drops to 2 in. Hg, then quickly rises to 25 in. Hg, and then settles back to 17 in. Hg. What does this vacuum gauge reading indicate?General Engine Diagnosis
  50. 150.A technician is diagnosing a vehicle with an intermittent misfire that occurs only when the engine is hot. They have performed all basic checks and component swaps without isolating the problem. Which diagnostic tool or technique would be most effective for identifying this type of heat-related, intermittent fault in the ignition system?Ignition System Diagnosis and Repair