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Automotive Service Excellence (ASE) A8 Engine Performance practice questions

230 free questions with answers and explanations.

Practice test
  1. 151.A technician is diagnosing an engine that occasionally stalls at idle and has a consistent, slight vibration at all RPMs, not tied to engine speed. The vibration is felt more through the chassis than directly from the engine. What should the technician investigate first?General Engine Diagnosis
  2. 152.A technician is diagnosing an engine with a misfire on cylinder #3. They use a test light connected to battery voltage to probe the coil primary trigger wire while cranking the engine. The test light flashes brightly. What does this indicate about the ignition coil primary circuit for cylinder #3?Ignition System Diagnosis and Repair
  3. 153.A technician observes a vacuum gauge reading that is consistently low (around 10-12 in. Hg) and steady at idle. As the engine RPM is increased quickly, the vacuum momentarily drops to near zero and then recovers to a slightly higher, but still low, reading. What does this pattern most likely indicate?General Engine Diagnosis
  4. 154.A technician is diagnosing a vehicle that consistently consumes 1.5 quarts of oil every 500 miles, but there is no visible blue smoke from the exhaust, even during varied driving conditions. There are also no external oil leaks evident. What is the most likely cause of this oil consumption?General Engine Diagnosis
  5. 155.A technician is performing a diagnostic on a vehicle experiencing an intermittent misfire under heavy acceleration. Using an oscilloscope, they observe the secondary ignition waveform. On the misfiring cylinder, the spark line (firing line) is significantly shorter and lower in voltage than normal, and the spark duration is reduced. What does this waveform pattern MOST likely indicate?Ignition System Diagnosis and Repair
  6. 156.A technician performs a cylinder leakage test on cylinder #4. With the piston at Top Dead Center (TDC) on the compression stroke, 100 PSI of compressed air is applied. The gauge on the leakage tester indicates 30% leakage, and a noticeable hissing sound is heard from the oil filler cap. What does this indicate?General Engine Diagnosis
  7. 157.A vehicle experiences intermittent misfires and hesitation, particularly during damp weather. The technician inspects the ignition coil and finds no cracks, but notices some corrosion on the coil tower terminals. The spark plug wires are relatively new. What is the MOST likely cause of the intermittent misfires?Ignition System Diagnosis and Repair
  8. 158.A technician is diagnosing an engine that has a rhythmic 'thump' or 'clunk' noise that is directly proportional to engine RPM and becomes louder under load. The noise is present at all engine temperatures. What is the MOST likely cause?General Engine Diagnosis
  9. 159.A client complains of an engine misfire that primarily occurs under heavy acceleration. A technician performs a resistance test on the spark plug wires and finds that one wire has a resistance of 35,000 ohms, while the others are all within the 5,000-15,000 ohm range. What is the most appropriate next step for the technician?Ignition System Diagnosis and Repair
  10. 160.A technician is diagnosing a vehicle with a P0353 (Ignition Coil 'C' Primary/Secondary Circuit Malfunction) code. After checking power and ground to the coil, which are good, they measure the resistance of the coil primary winding and find it to be 0.1 ohms. The manufacturer specification for primary resistance is 0.5-1.5 ohms. What does this measurement indicate?Ignition System Diagnosis and Repair
  11. 161.A technician is diagnosing an engine with a complaint of significant power loss, especially under load, and a notable decrease in fuel economy. A vacuum gauge reading at idle is slightly low (15 in. Hg) and when the throttle is snapped open, the needle drops to near zero, then slowly rises to about 18 in. Hg, but then gradually drops back to 15 in. Hg and continues to slowly fall. What condition is indicated by this vacuum gauge behavior?General Engine Diagnosis
  12. 162.A technician is diagnosing a vehicle with a persistent misfire on cylinder #2. They perform a power balance test and confirm the misfire. Next, they use a spark tester to check for spark at the cylinder #2 spark plug wire, and observe a strong, consistent blue spark. What should the technician's NEXT diagnostic step be, considering these findings?Ignition System Diagnosis and Repair
  13. 163.A vehicle exhibits a consistent, dull, heavy 'thud' or 'rumble' that is proportional to engine RPM and becomes significantly more pronounced under heavy engine load. The noise is originating from the lower part of the engine block. What is the MOST likely cause?General Engine Diagnosis
  14. 164.A vehicle exhibits excessive oil consumption (1 quart per 1,000 miles) but shows no external oil leaks. The exhaust has a bluish tint, especially during acceleration after idling. What is the most likely cause?General Engine Diagnosis
  15. 165.A technician is performing a compression test on an engine. All cylinders show readings between 140-150 PSI, except for cylinder #3 which reads 90 PSI. A small amount of oil is added to cylinder #3, and the compression test is repeated, resulting in a reading of 135 PSI for cylinder #3. What does this indicate?General Engine Diagnosis
  16. 166.A technician is diagnosing an engine that runs rough, has reduced power, and a vacuum gauge shows a steady reading of 14 in. Hg at idle. When the engine is shut off, the vacuum gauge quickly drops to zero. What does this indicate?General Engine Diagnosis
  17. 167.A technician is diagnosing a vehicle with a consistent misfire on cylinder #2. After performing a cylinder power balance test, they notice that shorting out cylinder #2's spark plug wire causes no change in engine RPM. Shorting out other cylinders' spark plug wires causes a noticeable drop in RPM. What does this indicate?General Engine Diagnosis
  18. 168.A client complains that their vehicle's engine emits a constant 'hissing' sound from the intake manifold area and runs with a high, unstable idle. Which of the following is the MOST probable cause?General Engine Diagnosis
  19. 169.A technician is performing a diagnostic on a modern vehicle with a no-start condition. There are no diagnostic trouble codes (DTCs) stored. They verify battery voltage is good. They then check for spark at the plugs and find none. Next, they use a scan tool to observe engine RPM during cranking, and it reads '0 RPM'. What is the most probable cause of the no-start condition?Ignition System Diagnosis and Repair
  20. 170.A client complains of a 'check engine' light and rough running, particularly when the engine is cold. A scan tool reveals a P0301 (Cylinder 1 Misfire) code. After swapping the spark plug and coil-on-plug (COP) from cylinder 1 to cylinder 2 with no change in the misfire location, the technician decides to test the primary circuit of the ignition coil. What is the next logical step to diagnose the primary circuit issue, assuming the power supply to the coil is confirmed good?Ignition System Diagnosis and Repair
  21. 171.During a routine inspection, a technician notices that the engine's crankcase breather hose is collapsed and severely restricted. How might this condition affect engine operation and oil consumption?General Engine Diagnosis
  22. 172.A technician observes a vacuum gauge reading that is consistently low, around 10-12 in. Hg, but remains steady at idle. When the engine is revved, the needle drops to near zero and then slowly returns to the low idle reading. What does this indicate?General Engine Diagnosis
  23. 173.A technician is diagnosing an engine that exhibits a consistent, rhythmic 'knocking' sound that is loudest at idle and becomes less noticeable as RPM increases. The sound is present whether the engine is hot or cold. What is the MOST likely source of this noise?General Engine Diagnosis
  24. 174.A technician is diagnosing a vehicle with an intermittent misfire under heavy load. They suspect a weak spark due to a failing ignition coil. Using an oscilloscope, they observe that the coil's inductive kick (firing voltage) is consistently high (e.g., 25kV-30kV) while the spark line duration is relatively short (e.g., 0.5ms). All spark plugs are new. What does this combination of high firing voltage and short spark duration most likely indicate?Ignition System Diagnosis and Repair
  25. 175.A vehicle with a distributor-based ignition system exhibits a consistent misfire under acceleration. The technician notes that the misfire becomes more pronounced as engine RPM increases. Upon inspection, the distributor cap and rotor appear worn, with visible carbon tracking. What is the MOST likely cause of this symptom?Ignition System Diagnosis and Repair
  26. 176.A technician performs a 'wet' compression test on cylinder #3 after a 'dry' test showed a significantly low reading. The dry reading was 90 psi, and the wet reading is 140 psi. What does this result indicate?General Engine Diagnosis
  27. 177.A technician is diagnosing a vehicle with a misfire on cylinder #4. They use a spark tester to check for spark at the spark plug wire (or COP unit). The spark tester shows a very weak, orange spark that struggles to jump the gap. The technician has already confirmed good power and ground to the coil, and the spark plug is new. What is the most likely cause of the weak spark?Ignition System Diagnosis and Repair
  28. 178.A technician is diagnosing an engine with a persistent P0302 misfire code (Cylinder 2 Misfire Detected). After confirming spark and fuel delivery to cylinder #2, the technician performs a relative compression test using a scanner. The relative compression for cylinder #2 is significantly lower than the other cylinders. Which of the following spark plug conditions would MOST likely be observed on cylinder #2's spark plug due to this low compression?Ignition System Diagnosis and Repair
  29. 179.A technician is using an inductive timing light to check the ignition timing on an older vehicle with a distributor. They notice that the timing mark appears to jump around erratically, and the engine runs rough. All spark plugs and wires are confirmed to be in good condition. What is the most probable cause of the erratic timing light reading and rough running?Ignition System Diagnosis and Repair
  30. 180.A technician is performing a cylinder leakage test on an engine. With cylinder #1 at Top Dead Center (TDC) on the compression stroke, 100 psi of compressed air is applied. The gauge reads 60% leakage, and a hissing sound is heard from the exhaust pipe. What does this indicate?General Engine Diagnosis
  31. 181.A technician is diagnosing an engine with a complaint of a consistent, loud 'rumbling' or 'growling' noise that is most prominent when the engine is under load, such as driving uphill or accelerating. The noise is less noticeable at idle or during light cruising. What is the most likely cause?General Engine Diagnosis
  32. 182.A technician is performing a diagnostic check on a vehicle experiencing a rough idle and occasional stalling. They connect a scan tool and observe that the ignition timing is fluctuating erratically, even at a steady RPM. Which of the following components is LEAST likely to be the cause of this erratic timing?Ignition System Diagnosis and Repair
  33. 183.A technician is diagnosing an engine with a rough idle and a constant exhaust 'puffing' sound. A vacuum gauge is connected to the intake manifold, and the needle fluctuates rapidly and erratically between 10 and 15 in. Hg. What does this vacuum gauge reading most likely indicate?General Engine Diagnosis
  34. 184.A technician is diagnosing a vehicle with an intermittent misfire that seems to worsen during acceleration. Using a digital multimeter, they measure the resistance of a spark plug wire at 25,000 ohms. The manufacturer's specification for spark plug wire resistance is typically 5,000 to 12,000 ohms per foot. Assuming the wire is 1.5 feet long, what is the most likely conclusion regarding this spark plug wire?Ignition System Diagnosis and Repair
  35. 185.A technician is diagnosing an engine that has a noticeable 'hissing' sound coming from the intake manifold area and a consistently high idle speed that is difficult to reduce. Which of the following is the most probable cause?General Engine Diagnosis
  36. 186.A client reports that their vehicle's engine runs smoothly at idle but develops a significant vibration and loss of power only when under load, such as climbing a hill or accelerating briskly. The vibration is directly felt from the engine and is RPM-dependent. A scan tool shows no misfire codes. What is the most likely cause?General Engine Diagnosis
  37. 187.A technician is performing an engine condition diagnosis. The vehicle starts and runs, but the engine experiences a severe, consistent vibration that feels like a 'jackhammer' and is directly proportional to engine RPM. A cylinder power balance test shows that cylinder #5 is completely dead, with no RPM drop when its spark is disabled. What is the most likely cause?General Engine Diagnosis
  38. 188.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
  39. 189.A technician is diagnosing a no-start condition on a vehicle equipped with a Coil-On-Plug (COP) ignition system. They have confirmed that the engine cranks, but there is no spark from any of the ignition coils. Using a multimeter, they check for power and ground at the COP connectors and find both are present. What is the NEXT logical step in the diagnostic process?Ignition System Diagnosis and Repair
  40. 190.A vehicle owner complains that their car runs rough, especially at idle, and occasionally stalls after being refueled. The 'Check Engine' light is illuminated with a DTC P0446, indicating 'Evaporative Emission Control System Vent Control Circuit Malfunction'. Which component is MOST likely at fault?Emissions Control Systems Diagnosis and Repair
  41. 191.A technician is diagnosing a vehicle with a complaint of poor engine performance, especially under load, and a noticeable 'whooshing' or 'hissing' sound from the engine compartment. The scan tool shows positive fuel trims (STFT and LTFT) on both banks, and a P0171 (System Too Lean Bank 1) code is present. A visual inspection reveals no obvious leaks. Which of the following is the MOST likely cause?Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair
  42. 192.A vehicle owner reports that their vehicle occasionally experiences a noticeable loss of power and hesitation during acceleration, particularly when the fuel tank is less than a quarter full. The issue is intermittent and does not consistently trigger any diagnostic trouble codes (DTCs). When the fuel tank is full, the problem is rarely observed. What is the MOST likely cause of this complaint?Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair
  43. 193.A technician is performing a cylinder leakage test on cylinder #3 of an engine that has a rough idle and a misfire. With the piston at Top Dead Center (TDC) on the compression stroke, compressed air is applied. The technician hears a distinct hissing sound coming from the engine's exhaust pipe. What does this indicate?General Engine Diagnosis
  44. 194.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
  45. 195.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
  46. 196.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
  47. 197.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
  48. 198.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
  49. 199.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
  50. 200.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