Transcript Goodheart-Willcox Publisher | Modern Automotive Technology

by
Russell Krick
Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only
© 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-actuated
devices 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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© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only
Advanced Scan Tool
Tests
 Actuator tests
 most scan tools can switch computercontrolled 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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Permission granted to reproduce for educational use only
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only
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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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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Permission granted to reproduce for educational use only
© Goodheart-Willcox Co., Inc.
Permission granted to reproduce for educational use only
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 TemperatureRelated Problems
Freeze spray on the ECM
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Finding TemperatureRelated 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 with
a 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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Scope Test
Patterns
A. Superimposed display
Patterns 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
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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 Airflow
Sensor Pattern
As flow increases, an analog airflow meter
should produce more voltage
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Mass Airflow
Sensor 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 Fuel
Injector 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
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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© Goodheart-Willcox Co., Inc.
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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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Analyzer
Digital Display
Cranking tests
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Running tests
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Analyzer
Connection
Coil separate from
distributor
Unitized coil
distributor
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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 of
hot or moving parts
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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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Cranking Balance Test
 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
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Cranking Balance Test
All cylinders have
the same
compression
Lower compression
on cylinder 5
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