Diagnostic Basics
What is the name of the process that starts with verifying the customer’s concern and ends with confirming the repair?
Strategy-based diagnostic process
What tool can help locate engine noises?
Mechanical or electronic stethoscope
What is the typical vacuum reading for a properly running engine at idle?
17" to 21" of mercury
What does a cylinder power balance test measure?
Each cylinder’s output by disabling one at a time and measuring rpm drop
What does a cylinder leakage test determine?
Severity and location of a compression leak
Name two tools used to assess the mechanical condition of an engine.
Compression tester, vacuum gauge, pressure transducer, cylinder leakage tester, scan tool, stethoscope
What does an abnormal cranking rhythm indicate?
Mechanical or compression-related issues
Where is engine vacuum measured?
Intake manifold
What indicates a correctly operating cylinder during a power balance test?
A substantial rpm drop when disabled
If air is heard leaking out the throttle body during a leakage test, what is leaking?
Intake Valve
What is the first step in diagnosing an engine mechanical concern?
Verify the customer’s concern
What is the best clue for diagnosing vibrations?
Determine the frequency of the vibration
Name one condition that can cause low vacuum readings at higher speeds.
Restricted exhaust, faulty ignition timing, faulty variable valve timing, faulty EGR valve
What is the purpose of a cranking compression test?
To determine if a misfire is caused by a compression problem
What position should the piston be in during a leakage test?
Top dead center
Which tool provides the most accurate vacuum readings?
Pressure transducer
What does slowing of the starter motor during cranking indicate?
Compression stroke on a cylinder with significant compression
What does a steady but low vacuum reading at idle indicate?
Mechanical condition issue or incorrect valve timing
Name two conditions that a running compression test can reveal.
Flat cam lobes, broken valve springs, carboned-up valves, restricted intake/exhaust passages
Name two possible leak locations found during a leakage test.
Past piston rings, intake/exhaust valves, head gasket, into cooling system
What is unethical and illegal when diagnosing engine problems?
Charging for diagnosis without performing it correctly
Name one failure that can cause engine noise.
Worn bearings, piston slap, valve train issues
Which tool can graphically display vacuum readings?
Pressure transducer on a lab scope
What are two requirements for an accurate compression test?
Engine at operating temperature, spark plugs removed, battery fully charged, throttle wide open, at least five compression pulses per cylinder
What does bubbling in the coolant during a leakage test indicate?
Cracked head or bad head gasket