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

3. 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)

6. 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

7. Strategy-Based Diagnostics

8. Troubleshooting Chart

10. 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

11. Pressure Gauge Measures pressure that is higher than atmospheric pressure Used for: fuel pump output pressure testing turbocharger boost testing exhaust back pressure testing

12. Vacuum Gauge Diagnosis

13. Vacuum-Pressure Gauge Set up to measure boost on a road test

14. Used to check vacuum-actuateddevices and vacuum diaphragms

15. Hand Vacuum Pump Connect the pump, pump the handle, and see if the device holds a vacuum

17. Diesel Engine Testers

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

19. 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

20. Advanced Scan Tool Tests Datastream “live” electrical values read the scan tool screen to see computer input and output values

22. 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

24. 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

25. Terminal Voltage Chart

26. 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

27. Breakout Box

29. 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

30. 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

32. 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

34. Finding Temperature-Related Problems Freeze spray on the ECM

35. Finding Temperature-Related Problems Heat gun on the ECM

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

38. Dynamometer Using a five-gas analyzer witha dynamometer

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

41. Oscilloscope Screen A. 25,000 volt scale B. 50,000 volt scale C. Time scale milliseconds D. Time scale degrees

42. 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

43. 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

44. Primary Waveform

45. Secondary Waveform

46. A. Superimposed display Patterns on top of each other—checks that all patterns are uniform

47. Distributorless Waveform True spark is on compression stroke Wasted spark is on exhaust stroke

48. Magnetic Sensor Pattern Probe across sensor leads

49. Hall-Effect Sensor Oscilloscope connection

50. Hall-Effect Sensor Pattern The sensor signal frequency should increase as engine speed increases

51. Optical Sensor Pattern If the shutter widths vary, the pulse widths vary

52. Crankshaft Position Sensor Oscilloscope connection

53. Crankshaft Position Sensor Pattern

54. Scope connection Throttle Position Sensor

55. The TPS should produce a smooth curve as the throttle is opened and closed Throttle Position Sensor Pattern

56. A switching-type TPS should produce a good square wave without ringing Throttle Position Sensor Pattern

57. Scope connection MAP Sensor

58. The digital waveform frequency should increase as engine speed increases MAP Sensor Pattern

59. Analog waveform amplitude should increase as engine speed increases MAP Sensor Pattern

60. Jumpers connect power to the sensor Mass Airflow Sensor

61. As flow increases, an analog airflow meter should produce more voltage Mass AirflowSensor Pattern

62. A digital waveform frequency usually increases with airflow Mass AirflowSensor Pattern

63. Oscilloscope connection Knock Sensor

64. Analog waveform Knock Sensor Pattern

65. Electronic FuelInjector Patterns A. Normal B. Stuck C. Open D. Partial short

66. Oscilloscope connection ECM Scope Tests

67. Reference voltage ECM Scope Tests

68. Flight Record Test Stores the sensor waveforms in a scope’s memory for playback after a road test Useful for checking an intermittent condition

69. Flight Record Test Normal, consistent signal Signal breakdown

71. 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

72. Engine Analyzer

73. AnalyzerDigital Display Cranking tests Running tests

74. Analyzer Connection Coil separate from distributor

75. Distributorless ignition Analyzer Connection

76. Direct ignition Analyzer Connection

77. Make sure all leads are clear ofhot or moving parts Analyzer Connection

78. 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

79. 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

80. 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

81. 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%)

82. 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

83. Cranking Balance Test All cylinders have the same compression