publisher the goodheart-willcox co., inc. tinley park, illinois
DESCRIPTION
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois. PowerPoint for. Modern Automotive Technology. by Russell Krick. Chapter 46. Advanced Diagnostics. Contents. Advanced diagnostics Vacuum and pressure gauge tests Vacuum pump tests Diesel engine testers Advanced scan tools - PowerPoint PPT PresentationTRANSCRIPT
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Publisher
The Goodheart-Willcox Co., Inc.Tinley Park, Illinois
by
Russell Krick
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
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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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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 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 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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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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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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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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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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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
Breakout Box
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Breakout Box
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Electromagnetic Interference
Occurs when an induced voltage enters another system’s 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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Digital Pyrometer An electronic device used to measure
temperature engine operating temperature exhaust temperature—catalytic converter coolant temperature sensor temperature ambient temperature air conditioning system temperatures
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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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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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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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A. Superimposed displayPatterns on top of each other—checks that all patterns are uniform
B. Parade display
Patterns side by side in firing order—compares firing voltages
C. Stacked display
Cylinders one above the other—compares duration of events
Scope Test Patterns
Scope Test Patterns
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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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Scope connection
Throttle Position Sensor
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The TPS should produce a smooth curve as the throttle is opened and closed
Throttle Position Sensor Pattern
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A switching-type TPS should produce a good square wave without ringing
Throttle Position Sensor Pattern
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Scope connection
MAP Sensor
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The digital waveform frequency should increase as engine speed increases
MAP Sensor Pattern
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Analog waveform amplitude should increase as engine speed increases
MAP Sensor Pattern
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Jumpers connect power to the sensor
Mass Airflow Sensor
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As flow increases, an analog airflow meter should produce more voltage
Mass AirflowSensor Pattern
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A digital waveform frequency usually increases with airflow
Mass AirflowSensor Pattern
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Oscilloscope connection
Knock Sensor
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Analog waveform
Knock Sensor Pattern
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Electronic FuelInjector Patterns
A. Normal
B. Stuck
C. Open
D. Partial short
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Oscilloscope connection
ECM Scope Tests
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Reference voltage
ECM Scope Tests
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Flight Record Test
Stores the sensor waveforms in a scope’s 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 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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Distributorless ignition
Analyzer Connection
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Direct ignition
Analyzer Connection
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Make sure all leads are clear ofhot or moving parts
Analyzer Connection
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Coil Output Test
Measures the maximum available voltage produced by the ignition coil
Spark plug requires 5–20 kV Coil should have higher reserve voltage
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Coil Output Test Run engine at 1000–1500 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 15–20 kV
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Cylinder Balance Test
Measures the power output from each of the engine’s 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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Checks the engine’s 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
Cranking Balance Test
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Cranking Balance Test
All cylinders have the same
compression
Lower compression on cylinder 5