publisher the goodheart-willcox co., inc. tinley park, illinois

© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

Publisher

The Goodheart-Willcox Co., Inc.Tinley Park, Illinois

by

Russell Krick


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)


Isolating electromagnetic interference Using a digital pyrometer Finding temperature-related performance

problems Using a dynamometer Using an oscilloscope Engine analyzer (computer analyzer)


Advanced methods used to troubleshoot difficult-to-locate problems


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


Strategy-Based Diagnostics


Troubleshooting Chart


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


Pressure Gauge

Measures pressure that is higher than atmospheric pressure

Used for: fuel pump output pressure testing turbocharger boost testing exhaust back pressure testing


Vacuum Gauge Diagnosis


Vacuum-Pressure Gauge

Set up to measure boost on a road test


Used to check vacuum-actuateddevices and vacuum diaphragms


Hand Vacuum Pump

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


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


Diesel Engine Testers


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


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



Datastream “live” electrical values read the scan tool screen to see

computer input and output values



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


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


Terminal Voltage Chart


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


Breakout Box


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


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


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


Finding Temperature-Related Problems

Freeze spray on the ECM


Finding Temperature-Related Problems

Heat gun on the ECM


Dynamometer Measures power output by loading the

engine Check acceleration, maximum power,

and on-road performance characteristics


Dynamometer

Using a five-gas analyzer witha dynamometer


Oscilloscope Displays voltages in relation to time Produces a line on a cathode ray tube

or liquid crystal screen


Oscilloscope Screen

A. 25,000 volt scale

B. 50,000 volt scale

C. Time scale milliseconds

D. Time scale degrees


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


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


Primary Waveform


Secondary Waveform


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


Distributorless Waveform

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


Magnetic Sensor Pattern

Probe across sensor leads


Hall-Effect Sensor

Oscilloscope connection


Hall-Effect Sensor Pattern

The sensor signal frequency should increase as engine speed increases


Optical Sensor Pattern

If the shutter widths vary, the pulse widths vary


Crankshaft Position Sensor



Crankshaft Position Sensor Pattern


Scope connection

Throttle Position Sensor


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

Throttle Position Sensor Pattern


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

Throttle Position Sensor Pattern


Scope connection

MAP Sensor


The digital waveform frequency should increase as engine speed increases

MAP Sensor Pattern


Analog waveform amplitude should increase as engine speed increases

MAP Sensor Pattern


Jumpers connect power to the sensor

Mass Airflow Sensor


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

Mass AirflowSensor Pattern


A digital waveform frequency usually increases with airflow

Mass AirflowSensor Pattern



Knock Sensor


Analog waveform

Knock Sensor Pattern


Electronic FuelInjector Patterns

A. Normal

B. Stuck

C. Open

D. Partial short



ECM Scope Tests


Reference voltage

ECM Scope Tests


Flight Record Test

Stores the sensor waveforms in a scope’s memory for playback after a road test

Useful for checking an intermittent condition


Flight Record Test

Normal, consistent signal

Signal breakdown


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


Engine Analyzer


AnalyzerDigital Display

Cranking tests Running tests


Analyzer Connection

Coil separate from distributor

Unitized coildistributor


Distributorless ignition

Analyzer Connection


Direct ignition

Analyzer Connection


Make sure all leads are clear ofhot or moving parts

Analyzer Connection


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


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


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


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%)


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


Cranking Balance Test

All cylinders have the same

compression

Lower compression on cylinder 5

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