Modern Automotive

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PowerPoint for
Modern Automotive Technology
by Russell Krick
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Chapter 46
Advanced Diagnostics
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Contents

• Advanced diagnostics
• Vacuum and pressure gauge tests
• Vacuum pump tests
• Diesel engine testers
• Advanced scan tools
• Checking computer terminal values
• Using a breakout box
• (Continued)

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Contents

• Isolating electromagnetic interference
• Using a digital pyrometer
• Finding temperature-related performance problems
• Using a dynamometer
• Using an oscilloscope
• Engine analyzer (computer analyzer)

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Advanced Diagnostics
Advanced methods used to troubleshoot
difficult-to-locate problems
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Diagnostic Techniques and Tools

• By using some advanced techniques and tools, a
  technician can diagnose the most difficult
  problems
• Some tools that may be used
• vacuum and pressure gauge
• scan tool
• breakout box
• engine analyzer with oscilloscope

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Strategy-Based Diagnostics
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Troubleshooting Chart
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Vacuum and Pressure Gauge Tests
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Vacuum Gauge

• Measures pressure that is lower than atmospheric
  pressure
• Used for
• fuel pump vacuum tests
• vacuum pump testing
• intake manifold vacuum testing
• vacuum solenoid testing

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Pressure Gauge

• Measures pressure that is higher than atmospheric
  pressure
• Used for
• fuel pump output pressure testing
• turbocharger boost testing
• exhaust back pressure testing

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Vacuum Gauge Diagnosis
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Vacuum-Pressure Gauge

• Set up to measure boost on a road test

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Vacuum Pump Tests

• Used to check vacuum-actuateddevices and vacuum
  diaphragms

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Hand Vacuum Pump

• Connect the pump, pump the handle, and see if the
  device holds a vacuum

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Diesel Engine Testers

• A set of pressure gauges and valves used to
  measure injector system pressure
• Measure various operating parameters
• fuel pump pressure and volume
• injector operation
• lubrication system pressure

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Diesel Engine Testers
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Advanced Scan Tools

• In addition to retrieving trouble codes, modern
  scan tools can be used for advanced diagnostic
  procedures

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Advanced Scan Tool Tests

• Snapshot
• instantaneous reading of the operating parameters
  present when a problem occurs
• useful when intermittent problems occur
• program the scan tool for a road test
• when the symptom occurs, capture the data
• return to the shop and review the snapshot data

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Advanced Scan Tool Tests

• Datastream
• live electrical values
• read the scan tool screen to see computer input
  and output values

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Advanced Scan Tool Tests

• Actuator tests
• most scan tools can switch computer-controlled
  actuators on and off
• allows the technician to verify operation
• the scan tool can fire an ignition coil, control
  the idle speed motor, disable a fuel injector,
  and perform a balance test

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Checking Computer Terminal Values
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Computer Terminal Voltage Checks

• Use a digital voltmeter
• Probe between the computer terminals and ground
• Do not pierce the wires
• Compare the terminal voltages to specified values

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Terminal Voltage Chart
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Breakout Box

• Allows the technician to check electrical values
  at specific pins on an ECM or in the system the
  ECM controls
• Inserted into wiring harness at the ECM

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Breakout Box
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Isolating Electromagnetic Interference
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Electromagnetic Interference

• Occurs when an induced voltage enters another
  systems wiring
• Sources
• loose, misrouted, or unshielded plug wires
• police and CB radios
• aftermarket accessories
• May cause noise in stereo speakers or a
  computer-controlled system malfunction

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Isolating Interference

• Turn off or disable circuits or devices
• remove the alternator drive belt
• turn accessories on and off
• If the problem goes away, the cause has been
  isolated
• Use an AM radio tuned between stations to probe
  for sources

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Using a Digital Pyrometer
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Digital Pyrometer

• An electronic device used to measure temperature
• engine operating temperature
• exhaust temperaturecatalytic converter
• coolant temperature
• sensor temperature
• ambient temperature
• air conditioning system temperatures

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Finding Temperature-Related Performance Problems
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Finding Temperature-Related Problems

• Freeze spray on the ECM

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Finding Temperature-Related Problems

• Heat gun on the ECM

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Using a Dynomometer
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Dynamometer

• Measures power output by loading the engine
• Check acceleration, maximum power, and on-road
  performance characteristics

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Dynamometer

• Using a five-gas analyzer witha dynamometer

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Using a Oscilloscope
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Oscilloscope

• Displays voltages in relation to time
• Produces a line on a cathode ray tube or liquid
  crystal screen

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Oscilloscope Screen

• A. 25,000 volt scale
• B. 50,000 volt scale
• C. Time scale milliseconds
• D. Time scale degrees

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Scope Sweep Rate

• Frequency or time division on screen
• Affects the horizontal, or time, measurement
• Set to match the waveform frequency to be
  analyzed
• a low sweep rate compresses the signal
• a high sweep rate expands the signal

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Ignition Patterns

• Primary
• low voltage ignition components
• the secondary circuit cannot work properly unless
  the primary circuit is in good condition
• Secondary
• high voltages needed to fire the spark plugs

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Primary Waveform
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Secondary Waveform
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Scope Test Patterns

• A. Superimposed display
• Patterns on top of each otherchecks that all
  patterns are uniform

B. Parade display Patterns side by side in
firing ordercompares firing voltages
C. Stacked display Cylinders one above the
othercompares duration of events
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Distributorless Waveform

• True spark is on compression stroke
• Wasted spark is on exhaust stroke

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Magnetic Sensor Pattern

• Probe across sensor leads

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Hall-Effect Sensor

• Oscilloscope connection

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Hall-Effect Sensor Pattern

• The sensor signal frequency should increase as
  engine speed increases

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Optical Sensor Pattern

• If the shutter widths vary, the pulse widths vary

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Crankshaft Position Sensor

• Oscilloscope connection

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Crankshaft Position Sensor Pattern
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Throttle Position Sensor

• Scope connection

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Throttle Position Sensor Pattern

• The TPS should produce a smooth curve as the
  throttle is opened and closed

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Throttle Position Sensor Pattern

• A switching-type TPS should produce a good square
  wave without ringing

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MAP Sensor

• Scope connection

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MAP Sensor Pattern

• The digital waveform frequency should increase as
  engine speed increases

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MAP Sensor Pattern

• Analog waveform amplitude should increase as
  engine speed increases

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Mass Airflow Sensor

• Jumpers connect power to the sensor

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Mass AirflowSensor Pattern

• As flow increases, an analog airflow meter should
  produce more voltage

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Mass AirflowSensor Pattern

• A digital waveform frequency usually increases
  with airflow

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Knock Sensor

• Oscilloscope connection

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Knock Sensor Pattern

• Analog waveform

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Electronic FuelInjector Patterns

• A. Normal
• B. Stuck
• C. Open
• D. Partial short

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ECM Scope Tests

• Oscilloscope connection

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ECM Scope Tests

• Reference voltage

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Flight Record Test

• Stores the sensor waveforms in a scopes memory
  for playback after a road test
• Useful for checking an intermittent condition

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Flight Record Test

• Normal, consistent signal
• Signal breakdown

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Engine Analyzer
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Engine Analyzer

• Group of test instruments in a large, roll-around
  cabinet
• scope
• tach-dwell meter
• volt-ohmmeter
• exhaust gas analyzer
• May be equipped with a modem to allow
  communication over telephone lines

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Engine Analyzer
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AnalyzerDigital Display

• Cranking tests Running tests

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Analyzer Connection

• Coil separate from distributor

Unitized coildistributor
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Analyzer Connection

• Distributorless ignition

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Analyzer Connection

• Direct ignition

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Analyzer Connection

• Make sure all leads are clear ofhot or moving
  parts

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Coil Output Test

• Measures the maximum available voltage produced
  by the ignition coil
• Spark plug requires 520 kV
• Coil should have higher reserve voltage

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Coil Output Test

• Run engine at 10001500 rpm
• Select secondary parade pattern
• Note the spark plug firing voltages
• Using insulated pliers, disconnect a plug wire
  (or install a spark tester before startup)
• The open circuit should cause one firing line to
  rise to maximum coil output
• Reconnect as soon as possible

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Load Test

• Snap acceleration test
• Measures the spark plug firing voltage when an
  engine is accelerated
• voltage requirements increase
• Set the scope to parade
• Quickly open and release the throttle valve
• The firing lines should be no more than 75 of
  coil output, or about 1520 kV

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Cylinder Balance Test

• Measures the power output from each of the
  engines cylinders
• The analyzer kills the spark of a selected
  cylinder, allowing the technician to observe and
  compare the rpm drop
• All cylinders should have the same percentage of
  rpm drop (within 5)

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Cranking Balance Test

• Checks the engines mechanical condition
• Measures how much current is drawn by the starter
  motor as each cylinder goes through its
  compression stroke
• High current means high compression pressure
• Low current means low compression pressure

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Cranking Balance Test

• All cylinders have the same compression

Lower compression on cylinder 5