2. OBJECTIVES After studying Chapter 21, the reader will be able to:
Prepare for ASE Engine Performance (A8) certification test content area “B” (Ignition System Diagnosis and Repair).
Describe the procedure used to check for spark.
Discuss what to inspect and look for during a visual inspection of the ignition system.
List the steps necessary to check and/or adjust ignition timing on engines equipped with a distributor.
Describe how to test the ignition system using an oscilloscope.

3. CHECKING FOR SPARK
Typical causes of a no-spark (intermittent spark) condition include the following:
Weak ignition coil
Low or no voltage to the primary (positive) side of the coil
High resistance or open coil wire, or spark plug wire
Negative side of the coil not being pulsed by the ignition module
Defective pickup coil
Defective module

4. CHECKING FOR SPARK
FIGURE 21-1 A spark tester looks like a regular spark plug with an alligator clip attached to the shell. This tester has a specified gap that requires at least 25,000 volts (25 kV) to fire.

5. CHECKING FOR SPARK
FIGURE 21-2 A close-up showing the recessed center electrode on a spark tester. It is recessed 3/8 in. into the shell and the spark must then jump another 3/8 in. to the shell for a total gap of 3/4 in.

6. ELECTRONIC IGNITION TROUBLESHOOTING PROCEDURE
When troubleshooting any electronic ignition system for no spark, follow these steps to help pinpoint the exact cause of the problem:
Turn the ignition on (engine off) and, using either a voltmeter or a test light, test for battery voltage available at the positive terminal of the ignition coil.
Connect the voltmeter or test light to the negative side of the coil and crank the engine.

7. IGNITION COIL TESTING USING AN OHMMETER
To test the primary coil winding resistance, take the following steps:
Set the meter to read low ohms.
Measure the resistance between the positive terminal and the negative terminal of the ignition coil.
To test the secondary coil winding resistance, follow these steps:
Set the meter to read kilohms (kΩ).
Measure the resistance between either primary terminal and the secondary coil tower.

8. IGNITION COIL TESTING USING AN OHMMETER
FIGURE 21-3 Checking an ignition coil using a multimeter set to read ohms. (Courtesy of Fluke Corporation)

9. PICKUP COIL TESTING
The pickup coil can be tested for proper voltage output.
During cranking, most pickup coils should produce a minimum of 0.25 volt AC.
This can be tested with the distributor out of the vehicle by rotating the distributor drive gear by hand.
FIGURE 21-4 Measuring the resistance of an HEI pickup coil using a digital multimeter set to the ohms position. The reading on the face of the meter is kΩ or 796 ohms in the middle of the 500- to 1,500-ohm specifications.

10. TESTING MAGNETIC SENSORS
If the sensor is removed from the engine, hold a metal (steel) object against the end of the sensor.
It should exert a strong magnetic pull on the steel object. If not, replace the sensor.
Then, the sensor can be tested using a digital meter set to read AC volts.

11. TESTING MAGNETIC SENSORS
FIGURE 21-5 An AC voltage is produced by a magnetic sensor. Most sensors should produce at least 0.1 volt AC while the engine is cranking if the pickup wheel has many teeth. If the pickup wheel has only a few teeth, you may need to switch the meter to read DC volts and watch the display for a jump in voltage as the teeth pass the magnetic sensor. (Courtesy of Fluke Corporation)

12. TESTING HALL-EFFECT SENSORS
As with any other sensor, the output of the Hall-effect sensor should be tested first.
Using a digital voltmeter, check for the presence of a changing DC (digital hi-low) voltage when the engine is being cranked.
The best test is to use an oscilloscope and observe the waveform.

13. TESTING HALL-EFFECT SENSORS
FIGURE 21-6 (a) The connection required to test a Hall-effect sensor. (b) A typical waveform from a Hall-effect sensor.

14. TESTING OPTICAL SENSORS
FIGURE 21-7 (a) The low-resolution signal has the same number of pulses as the engine has cylinders. (b) A dual-trace pattern showing both the low-resolution signal and the high-resolution signals that usually represent 1 degree of rotation. (Courtesy of Fluke Corporation)

15. BAD WIRE? REPLACE THE COIL!
FIGURE 21-8 A track inside an ignition coil is not a short, but rather a low-resistance path or hole that has been burned through from the secondary wiring to the steel core.

16. TESTING FOR POOR PERFORMANCE
A simple method of testing a distributorless (waste-spark systems) ignition with the engine off involves removing the spark plug wires (or connectors) from the spark plugs (or coils or distributor cap) and installing short lengths (2 in.) of rubber vacuum hose in series.
FIGURE 21-9 A length of vacuum hose being used for a coil wire. The vacuum hose is conductive because of the carbon content of the rubber in the hose. This hose measures only 1,000 ohms and was 1 ft long, which is lower resistance than most spark plug wires. Notice the spark from the hose’s surface to the tip of a grounded screwdriver.

17. TESTING FOR POOR PERFORMANCE
FIGURE Using a vacuum hose and a grounded test light to ground one cylinder at a time on a DIS. This works on all types of ignition systems and provides a method for grounding out one cylinder at a time without fear of damaging any component.

18. TESTING FOR A NO-START CONDITION
A no-start condition (with normal engine cranking speed) can be the result of either no spark or no fuel delivery.
Computerized engine control systems use the ignition primary pulses as a signal to inject fuel—a port or throttle-body injection (TBI) style of fuel-injection system. If there is no pulse, then there is no squirt of fuel.

19. FIRING ORDER
Firing order means the order that the spark is distributed to the correct spark plug at the right time.
The firing order of an engine is determined by crankshaft and camshaft design.
The firing order is determined by the location of the spark plug wires in the distributor cap of an engine equipped with a distributor.
FIGURE The firing order is cast or stamped on the intake manifold on most engines that have a distributor ignition.

20. SECONDARY IGNITION INSPECTION
Inspect a distributor cap for a worn or cracked center carbon insert, excessive side insert wear or corrosion, cracks, or carbon tracks, and check the towers for burning or corrosion by removing spark plug wires from the distributor cap one at a time.

21. SECONDARY IGNITION INSPECTION
FIGURE Note where the high-voltage spark jumped through the plastic rotor to arc into the distributor shaft. Always check for a defective spark plug(s) when a defective distributor cap or rotor is discovered. If a spark cannot jump to a spark plug, it tries to find a ground path wherever it can.

22. SECONDARY IGNITION INSPECTION
FIGURE Carbon track in a distributor cap. These faults are sometimes difficult to spot and can cause intermittent engine missing. The usual cause of a tracked distributor cap (or coil, if it is a distributorless ignition) is a defective (open) spark plug wire.

23. SECONDARY IGNITION INSPECTION
FIGURE Corroded terminals on a waste-spark coil can cause misfire diagnostic trouble codes to be set.

24. SPARK PLUG WIRE INSPECTION
Spark plug wires should be visually inspected for cuts or defective insulation and checked for resistance with an ohmmeter.
Good spark plug wires should measure less than 10,000 ohms per foot of length.
Faulty spark plug wire insulation can cause hard starting or no starting in damp weather conditions.

25. SPARK PLUG WIRE INSPECTION
FIGURE This spark plug boot on an overhead camshaft engine has been arcing to the valve cover causing a misfire to occur.

26. SPARK PLUG WIRE INSPECTION
FIGURE Measuring the resistance of a spark plug wire with a multimeter set to the ohms position. The reading of kΩ( ohms) is okay because the wire is about 2 feet long. Maximum allowable resistance for a spark plug wire this long would be 20 kΩ(20,000 ohms).

27. SPARK PLUG WIRE PLIERS ARE A GOOD INVESTMENT
FIGURE Spark plug wire boot pliers are a handy addition to any toolbox.

28. SPARK PLUG SERVICE
Spark plugs should be inspected when an engine performance problem occurs and should be replaced regularly to ensure proper ignition system performance.
Many spark plugs have a service life of over 20,000 miles (32,000 kilometers).
Platinum-tipped original equipment spark plugs have a typical service life of 60,000 to 100,000 miles (100,000 to 160,000 kilometers).

29. ROUTE THE WIRES RIGHT!
FIGURE Always take the time to install spark plug wires back into the original holding brackets (wiring combs).

30. SPARK PLUG SERVICE
FIGURE When removing spark plugs, it is wise to arrange them so that they can be compared and any problem can be identified with a particular cylinder.

31. SPARK PLUG SERVICE
FIGURE A spark plug thread chaser is a low-cost tool that hopefully will not be used often, but is necessary to clean the threads before new spark plugs are installed.

32. SPARK PLUG SERVICE
FIGURE Since 1991, General Motors engines have been equipped with slightly (1/8 in. or 3 mm) longer spark plugs. This requires that a longer spark plug socket should be used to prevent the possibility of cracking a spark plug during installation. The longer socket is shown next to a normal 5/8 in. spark plug socket.

33. SPARK PLUG INSPECTION
Spark plugs are the windows to the inside of the combustion chamber.
A thorough visual inspection of the spark plugs often can lead to the root cause of an engine performance problem.
Two indications on spark plugs and their possible root causes in engine performance include the following:
Carbon fouling.
Oil fouling.
FIGURE An extended-reach spark plug that shows normal wear. The color and condition indicate that the cylinder is operating correctly.

34. SPARK PLUG INSPECTION
FIGURE Spark plug removed from an engine after a 500-mile race. Note the clipped side (ground) electrode. The electrode design and narrow (0.025 in.) gap are used to ensure that a spark occurs during extremely high engine speed operation. The color and condition of the spark plug indicate that near-perfect combustion has been occurring.

35. SPARK PLUG INSPECTION
FIGURE Typical worn spark plug. Notice the rounded center electrode. The deposits indicate a possible oil usage problem.

36. SPARK PLUG INSPECTION
FIGURE New spark plug that was fouled by a too-rich air-fuel mixture. The engine from which this spark plug came had a defective (stuck partially open) injector on this one cylinder only.

37. QUICK AND EASY SECONDARY IGNITION TESTS
FIGURE A water spray bottle is an excellent diagnostic tool to help find an intermittent engine miss caused by a break in a secondary ignition circuit component.

38. IGNITION TIMING
Generally, for testing, engines must be at idle with computer engine controls put into base timing, the timing of the spark before the computer advances the timing.
Pretiming Checks
Timing Light Connections
Determining Cylinder 1
Checking or Adjusting Ignition Timing
FIGURE Typical timing marks. The numbers of the degrees are on the stationary plate and the notch is on the harmonic balancer.

39. IGNITION TIMING
FIGURE Cylinder 1 and timing mark location guide.

40. IGNITION TIMING
FIGURE (a) Typical SPOUT connector as used on many Ford engines equipped with distributor ignition (DI). (b) The connector must be opened (disconnected) to check and/or adjust the ignition timing. On DIS/EDIS systems, the connector is called SPOUT/SAW (spark output/spark angle word).

41. SCOPE-TESTING THE IGNITION SYSTEM
Firing Line
Spark Line
Intermediate Oscillations
Transistor-On Point
Dwell Section
Pattern Selection
Superimposed.
Raster (stacked).
Display (parade).
Reading the Scope on Display (Parade)
Reading the Spark Lines

42. SCOPE-TESTING THE IGNITION SYSTEM
Spark Line Slope
Reading the Intermediate Section
Electronic Ignition and the Dwell Section
Dwell Variation (Distributor Ignition)
Coil Polarity
Acceleration Check
Rotor Gap Voltage

43. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Typical engine analyzer hookup that includes a scope display. (1) Coil wire on top of the distributor cap if integral type of coil; (2) number 1 spark plug connection; (3) negative side of the ignition coil; (4) ground (negative) connection of the battery.

44. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Clip-on adapters are used with an ignition system that uses an integral ignition coil. (Courtesy of Fluke Corporation)

45. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Typical secondary ignition oscilloscope pattern.

46. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE A single cylinder is shown at the top and a 4-cylinder engine at the bottom.(Courtesy of Fluke Corporation)

47. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Drawing shows what is occurring electrically at each part of the scope pattern.

48. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Typical secondary ignition pattern. Note the lack of firing lines on the superimposed pattern.

49. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Raster is the best scope position to view the spark lines of all the cylinders to check for differences. Most scopes display cylinder 1 at the bottom. The other cylinders are positioned by firing order above cylinder 1.

50. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE Display is the only position to view the firing lines of all cylinders. Cylinder 1 is displayed on the left (except for its firing line, which is shown on the right). The cylinders are displayed from left to right by firing order.

51. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE A downward-sloping spark line usually indicates high secondary ignition system resistance or an excessively rich air-fuel mixture.

52. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE An upward-sloping spark line usually indicates a mechanical engine problem or a lean air-fuel mixture.

53. SCOPE-TESTING THE IGNITION SYSTEM
FIGURE The relationship between the height of the firing line and length of the spark line can be illustrated using a rope. Because energy cannot be destroyed, the stored energy in an ignition coil must dissipate totally, regardless of engine operating conditions.

54. SCOPE-TESTING A WASTESPARK IGNITION SYSTEM
A handheld digital storage oscilloscope can be used to check the pattern of each individual cylinder.
Some larger scopes can be connected to all spark plug wires and therefore are able to display both power and waste-spark waveforms.
FIGURE A dual-trace scope pattern showing both the power and the waste spark from the same coil (cylinders 1 and 6). Note that the firing line is higher on the cylinder that is under compression (power); otherwise, both patterns are almost identical.

55. SCOPE-TESTING A COIL-ON-PLUG IGNITION SYSTEM
On a coil-on-plug (COP) type of ignition system, each individual coil can be shown on a scope and using the proper cables and adapters, the waveform for all of the cylinders can be viewed at the same time
FIGURE A secondary waveform of a Ford 4.6 liter V-8,showing three sparks occurring at idle speed.

56. IGNITION SYSTEM DIAGNOSIS

57. IGNITION SYSTEM DIAGNOSIS

58. IGNITION SYSTEM DIAGNOSIS

59. IGNITION SYSTEM DIAGNOSIS

60. IGNITION SYSTEM DIAGNOSIS

61. IGNITION SYSTEM DIAGNOSIS

62. SUMMARY
A thorough visual inspection should be performed on all ignition components when diagnosing an engine performance problem.
Platinum spark plugs should not be regapped after use in an engine.
A secondary ignition scope pattern includes a firing line, spark line, intermediate oscillations, and transistor-on and transistor-off points.
The slope of the spark line can indicate incorrect air-fuel ratio or other engine problems.

63. REVIEW QUESTIONS
Why should a spark tester be used to check for spark rather than a standard spark plug?
How do you test a pickup coil for resistance and AC voltage output?
What harm can occur if the engine is cranked or run with an open (defective) spark plug wire?
What are the sections of a secondary ignition scope pattern?
What can the slope of the spark line indicate about the engine?

64. CHAPTER QUIZ
Technician A says that the firing line shows the voltage that is required to fire the spark plug. Technician B says that spark line shows the duration of the spark inside the cylinder. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

65. CHAPTER QUIZ
Technician A says that the firing line shows the voltage that is required to fire the spark plug. Technician B says that spark line shows the duration of the spark inside the cylinder. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

66. CHAPTER QUIZ
2. Technician A says that a defective spark plug wire can cause an engine miss. Technician B says that a defective spark plug can cause an engine miss. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

67. CHAPTER QUIZ
2. Technician A says that a defective spark plug wire can cause an engine miss. Technician B says that a defective spark plug can cause an engine miss. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

68. CHAPTER QUIZ
3. The _____ sends a pulse signal to an electronic ignition module.
Ballast resistor
Pickup coil
Ignition coil
Condenser

69. CHAPTER QUIZ
3. The _____ sends a pulse signal to an electronic ignition module.
Ballast resistor
Pickup coil
Ignition coil
Condenser

70. CHAPTER QUIZ
4. Typical primary coil resistance specifications usually range from _____ ohms.
100 to 450
500 to 1,500
1 to 3
6,000 to 30,000

71. CHAPTER QUIZ
4. Typical primary coil resistance specifications usually range from _____ ohms.
100 to 450
500 to 1,500
1 to 3
6,000 to 30,000

72. CHAPTER QUIZ
5. Typical secondary coil resistance specifications usually range from _____ ohms.
100 to 450
500 to 1,500
1 to 3
6,000 to 30,000

73. CHAPTER QUIZ
5. Typical secondary coil resistance specifications usually range from _____ ohms.
100 to 450
500 to 1,500
1 to 3
6,000 to 30,000

74. CHAPTER QUIZ
6. Technician A says that an engine will not start and run if the ignition coil is tracked. Technician B says that one wire of any pickup coil must be grounded. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

75. CHAPTER QUIZ
6. Technician A says that an engine will not start and run if the ignition coil is tracked. Technician B says that one wire of any pickup coil must be grounded. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

76. CHAPTER QUIZ
7. Technician A says that a GM HEI distributor rotor can burn through and cause an engine miss during acceleration. Technician B says that a defective distributor cap can cause an engine miss during acceleration. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

77. CHAPTER QUIZ
7. Technician A says that a GM HEI distributor rotor can burn through and cause an engine miss during acceleration. Technician B says that a defective distributor cap can cause an engine miss during acceleration. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

78. CHAPTER QUIZ
8. The secondary ignition circuit can be tested using _____.
An ohmmeter
A test light
An ammeter
Both a and b

79. CHAPTER QUIZ
8. The secondary ignition circuit can be tested using _____.
An ohmmeter
A test light
An ammeter
Both a and b

80. CHAPTER QUIZ
9. Two technicians are discussing a no-start condition. During cranking, a magnet held over the coil moves and the engine backfires at times. Technician A says that a bad pickup coil or CKP sensor is the most likely cause. Technician B says that an open coil primary is the most likely cause. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

81. CHAPTER QUIZ
9. Two technicians are discussing a no-start condition. During cranking, a magnet held over the coil moves and the engine backfires at times. Technician A says that a bad pickup coil or CKP sensor is the most likely cause. Technician B says that an open coil primary is the most likely cause. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

82. CHAPTER QUIZ 10. Which sensor produces a square wave signal?
Magnetic sensor
Hall-effect sensor
Pickup coil
Both b and c

83. CHAPTER QUIZ 10. Which sensor produces a square wave signal?
Magnetic sensor
Hall-effect sensor
Pickup coil
Both b and c