Questions and Answers
When diagnosing an engine miss using a cylinder leakage test, Technician A says any cylinder with over 20% leakage has excessive leakage. Technician B says air leaking from the tailpipe indicates a cracked cylinder. Who is correct?
During a compression test, a cylinder has 40% of the specified compression reading. When a wet test is performed, the reading increases to 75% of the specified reading. What is the most likely cause of the low compression reading?
If a customer complains that the engine cranks but does not start, what should be checked first?
During a cylinder balance test on an engine with fuel injection, one cylinder provides very little RPM drop. Technician A suggests a misfiring ignition system; Technician B suggests an intake manifold vacuum leak. Who is correct?
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In a discussion on basic diagnostic procedures, Technician A says the most complicated diagnostic tests should be performed first. Technician B says to first question the customer. Who is correct?
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With the engine idling, a vacuum gauge connected to the intake manifold fluctuates between 15 to 20. These fluctuations may be caused by what?
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If oil is leaking from the crankshaft rear main bearing seal, Technician A says the oil seal could be faulty; Technician B says the PCV system may not be functioning. Who is correct?
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A high-pitched squealing noise is heard during hard acceleration. What is the most likely cause?
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A heavy thumping noise occurs with the engine idling, but the oil pressure is normal. What could be the cause?
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After a vehicle is parked overnight and started in the morning, the engine makes a lifter noise that disappears shortly after running. What is the likely cause?
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When using a compression tester, all cylinder readings are even but lower than specified. This could indicate what?
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Study Notes
Engine Diagnostic Tests
- A cylinder leakage test indicates excessive leakage if it exceeds 20%, with air escaping from the tailpipe suggesting an exhaust valve leak.
- For a compression test, if wet test results show increased compression, it likely reveals worn piston rings, not issues with valves or camshaft.
Initial Troubleshooting Steps
- When an engine cranks but won’t start, valve train operation should be the first check, as proper cranking indicates no battery issues.
Cylinder Balance Testing
- During a cylinder balance test, minimal RPM drop in one cylinder can suggest a misfiring ignition system or an intake manifold vacuum leak.
Diagnostic Procedure Guidelines
- Basic diagnostic protocols prioritize simple questions to customers about issues before performing complicated tests.
Vacuum Gauge Readings
- Fluctuations in a vacuum gauge (15 to 20 inches) while idling can indicate sticky valve stems and guides, as other factors would cause steady readings.
Oil Leak Causes
- An oil leak from the crankshaft rear main bearing seal could result from a faulty oil seal or malfunctioning PCV system.
Noise Diagnosis During Acceleration
- A high-pitched squeal during hard acceleration may point to a small leak in the exhaust manifold, distinct from other potential leak noises.
Thumping Noise at Idle
- A heavy thumping sound while idling may be caused by loose flywheel bolts, while worn components usually trigger noise during acceleration or startup.
Lifter Noise After Initial Start
- Lifter noise that vanishes shortly after starting indicates excessive lifter leak-down, while low oil pressure or level would cause a persistent noise.
Compression Tester Readings
- Even but low compression readings across all cylinders might suggest worn rings and cylinders, while adjacent low readings could indicate a blown head gasket.
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Description
Test your knowledge on engine repair with this cumulative flashcard set focused on diagnosing engine issues. Evaluate the effectiveness of cylinder leakage tests and other diagnostic techniques. Perfect for ASE A1 certification preparation.
