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CHAPTER 9 Ignition System Diagnosis and Service

CHAPTER 9 Ignition System Diagnosis and Service. OBJECTIVES. After studying Chapter 9, 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.

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CHAPTER 9 Ignition System Diagnosis and Service

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  1. CHAPTER 9 Ignition System Diagnosis and Service

  2. OBJECTIVES After studying Chapter 9, 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. • Explain how to test pickup coils, ignition coils, and spark plug wires. • Discuss how to current ramp ignition coils using a low ampere current clamp and a scope. • Describe how to test the ignition system using an oscilloscope.

  3. Burn kV Charging rise time Firing line Firing order Ignition timing Iridium spark plugs Millisecond (ms) sweep Module current limits Platinum spark plugs Spark line Spark tester KEY TERMS

  4. CHECKING FOR SPARK • In the event of a no-start condition, the first step should be to check for secondary voltage out of the ignition coil or to the spark plugs. • If the engine is equipped with a separate ignition coil, remove the coil wire from the center of the distributor cap, install a spark tester, and crank the engine. • A good coil and ignition system should produce a blue spark at the spark tester.

  5. FIGURE 9–1 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. CHECKING FOR SPARK

  6. FIGURE 9–2 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. CHECKING FOR SPARK

  7. CHECKING FOR SPARK • Typical causes of a no-spark (intermittent spark) condition include the following: • 1. Weak ignition coil • 2. Low or no voltage to the primary (positive) side of the coil • 3. High resistance or open coil wire, or spark plug wire • 4. Negative side of the coil not being pulsed by the ignition module, also called an ignition control module (ICM) • 5. Defective pickup coil • 6. Defective module

  8. Always Use a Spark Tester • A spark tester looks like a spark plug except it has a recessed center electrode and no side electrode. The tester commonly has an alligator clip attached to the shell so that it can be clamped on a good ground connection on the engine. A good ignition system should be able to cause a spark to jump this wide gap at atmospheric pressure. Without a spark tester, a technician might assume that the ignition system is okay, because it can spark across a normal, grounded spark plug.

  9. Always Use a Spark Tester • The voltage required to fire a standard spark plug when it is out of the engine and not under pressure is about 3,000 volts or less. An electronic ignition spark tester requires a minimum of 25,000 volts to jump the 3/4-in. gap. Therefore, never assume that the ignition system is okay because it fires a spark plug—always use a spark tester. Remember that an intermittent spark across a spark tester should be interpreted as a no-spark condition.

  10. IGNITION COIL TESTING • IGNITION COIL TESTING USING AN OHMMETER • CURRENT RAMPING IGNITION COILS • CURRENT RAMP TEST PROCEDURE

  11. FIGURE 9–3 Checking an ignition coil using a multimeter set to read ohms. IGNITION COIL TESTING USING AN OHMMETER

  12. The Magnetic Pickup Tool Test • All ignition coils are pulsed on and off by the ignition control module or PCM. When the coil charges and discharges, the magnetic field around the coil changes. This pulsing of the coil can be observed by holding the magnetic end of a pickup tool near an operating ignition coil. The magnet at the end of the pickup tool will move as the magnetic field around the coil changes.

  13. FIGURE 9–4 If the coil is working, the end of the magnetic pickup tool will move with the changes in the magnetic field around the coil. The Magnetic Pickup Tool Test

  14. FIGURE 9–5 A waveform showing the primary current flow through the primary windings of an ignition coil. IGNITION COIL TESTING USING AN OHMMETER

  15. FIGURE 9–6 Schematic of a typical waste-spark ignition system showing the location for the power feed and grounds. (Courtesy of Fluke Corporation) IGNITION COIL TESTING USING AN OHMMETER

  16. IGNITION COIL TESTING USING AN OHMMETER

  17. FIGURE 9–7 An example of a good coil current flow waveform pattern. Note the regular shape of the rise time and slope. Duration of the waveform may change as the module adjusts the dwell. The dwell is usually increased as the engine speed is increased. (Courtesy of Fluke Corporation) IGNITION COIL TESTING USING AN OHMMETER

  18. FIGURE 9–8 (a) A waveform pattern showing an open in the coil primary. (b) A shorted coil pattern waveform. (Courtesy of Fluke Corporation) IGNITION COIL TESTING USING AN OHMMETER

  19. IGNITION SENSOR TESTING • MAGNETIC SENSOR TESTING • HALL-EFFECT SENSOR TESTING • OPTICAL SENSOR TESTING

  20. FIGURE 9–9 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 0.796 kΩ or 796 ohms in the middle of the 500- to 1,500-ohm specifications. IGNITION SENSOR TESTING

  21. FIGURE 9–10 A typical pickup coil showing how the waveform is created as the timer core rotates inside the pole piece. IGNITION SENSOR TESTING

  22. FIGURE 9–11 (a) A voltage waveform of a pickup coil at low engine speed. (b) A current waveform of the current through the primary windings of the ignition coil at low engine speed. (c) A voltage waveform of a pickup coil at high speed. (d) A current waveform through the primary winding of the ignition coil at high engine speed. IGNITION SENSOR TESTING

  23. FIGURE 9–12 A diagnostic trouble code P0336 was displayed on a Tech 2 scan tool as the only code. IGNITION SENSOR TESTING

  24. FIGURE 9–13 The engine started and was running, but the Tech 2 displayed zero RPM. IGNITION SENSOR TESTING

  25. FIGURE 9–14 The old crankshaft showing the reluctor notches. The damage was not visible, but the engine started each time after the crankshaft was replaced. IGNITION SENSOR TESTING

  26. FIGURE 9–15 (a) The connection required to test a Halleffect sensor. (b) A typical waveform from a Hall-effect sensor. TESTIN IGNITION SENSOR TESTING G HALL-EFFECT SENSORS

  27. FIGURE 9–16 (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 and the high-resolution signals that usually represent 1 degree of rotation. IGNITION SENSOR TESTING

  28. Bad Wire? Replace the Coil! • When performing engine testing (such as a compression test), always ground the coil wire or disable the primary ignition circuit by removing the ignition fuse. If the spark cannot spark to ground, the coil energy can (and usually does) arc inside the coil itself, creating a low-resistance path to the primary windings or the steel laminations of the coil.

  29. Bad Wire? Replace the Coil! • This low-resistance path is called a track and could cause an engine miss under load even though all of the remaining component parts of the ignition system are functioning correctly. Often these tracks do not show up on any coil test, including most scopes. Because the track is a lower resistance path to ground than normal, it requires that the ignition system be put under a load for it to be detected; and even then, the problem such as an engine misfire may be intermittent.

  30. FIGURE 9–17 A track inside an ignition coil is not a short, but a low-resistance path or hole that has been burned through from the secondary wiring to the steel core. Bad Wire? Replace the Coil!

  31. Spark Plug Wire Pliers Are a Good Investment • Spark plug wires are often difficult to remove. Using good-quality spark plug wire plierssaves time and reduces the chance of harming the wire during removal.

  32. FIGURE 9–18 Corroded terminals on a waste-spark coil can cause misfire diagnostic trouble codes to be set. Spark Plug Wire Pliers Are a Good Investment

  33. FIGURE 9–19 This spark plug boot on an overhead camshaft engine has been arcing to the valve cover causing a misfire to occur. SPARK PLUG WIRE INSPECTION • VISUAL INSPECTION • OHMMETER TESTING

  34. FIGURE 9–20 Measuring the resistance of a spark plug wire with a multimeter set to the ohms position. The reading of 16.03 kΩ (16.030 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). High resistance spark plug wires can cause an engine misfire especially during acceleration. SPARK PLUG WIRE INSPECTION

  35. FIGURE 9–21 Spark plug wire boot pliers is a handy addition to any tool box. SPARK PLUG WIRE INSPECTION

  36. Use a Water Spray Bottle to Check for Bad Spark Plug Wires • For intermittent problems, use a spray bottle to apply a water mist to the spark plugs, distributor cap, and spark plug wires. With the engine running, the water may cause an arc through any weak insulating materials and cause the engine to miss or stall.

  37. FIGURE 9–22 A water spray bottle is an excellent diagnostic tool to help find an intermittent engine misfire caused by a break in a secondary ignition circuit component. Use a Water Spray Bottle to Check for Bad Spark Plug Wires

  38. SPARK PLUGS • SPARK PLUG CONSTRUCTION • RESISTOR SPARK PLUGS • PLATINUM SPARK PLUGS • IRIDIUM SPARK PLUGS • SPARK PLUG SERVICE

  39. FIGURE 9–23 Parts of a spark plug. SPARK PLUGS

  40. FIGURE 9–24 The heat range of a spark plug is determined by the distance the heat flows from the tip to the cylinder head. SPARK PLUGS

  41. FIGURE 9–25 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. SPARK PLUGS

  42. FIGURE 9–26 A spark plug thread chaser is a low-cost tool that hopefully will not be used often, but is necessary to use to clean the threads before new spark plugs are installed. SPARK PLUGS

  43. FIGURE 9–27 A normally worn spark plug that has a tapered platinum-tipped center electrode. SPARK PLUGS

  44. FIGURE 9–28 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. SPARK PLUGS

  45. FIGURE 9–29 Typical worn spark plug. Notice the rounded center electrode. The deposits indicate a possible oil usage problem. SPARK PLUGS

  46. FIGURE 9–30 New spark plug that was fouled by an overly rich air-fuel mixture. The engine from which this spark plug came had a defective (stuck partially open) injector on this one cylinder only. SPARK PLUGS

  47. SPARK PLUGS

  48. Two-Finger Trick • To help prevent overtightening a spark plug when a torque wrench is not available, simply use two fingers on the ratchet handle. Even the strongest service technician cannot overtighten a spark plug by using two fingers.

  49. FIGURE 9–31 Ignition timing marks are found on the harmonic balancers on engines equipped with distributors that can be adjusted for timing. IGNITION TIMING • PURPOSE • CHECKING IGNITION TIMING

  50. FIGURE 9–32 The initial (base) timing is where the spark plug fires at idle speed. The PCM then advances the timing based primarily on engine speed. IGNITION TIMING

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