2. 35
Chapter
Ignition System Diagnosis, Testing, and Repair

3. Objectives After studying this chapter, you will be able to:
List the symptoms produced by faulty ignition system components.
Diagnose typical ignition system problems.
Describe common tests used to find ignition system troubles.
Explain how to replace or repair ignition system parts.

4. Objectives
Describe safety practices to follow when testing or repairing an ignition system.
Correctly answer ASE certification test questions on the diagnosis and repair of ignition systems.

5. Ignition System Diagnosis
Visually inspect ignition system with and without engine running
Look for obvious problems
Loose primary connections
Disconnected spark plug
Loose direct ignition coil fasteners
Deteriorated secondary wire insulation
Damaged coil pack
Cracked distributor cap

6. Scanning Ignition System Problems
Scan tool can detect troubles in
Crankshaft position sensor
Camshaft position sensor
Knock sensor
Ignition coil(s) primary circuit
Ignition coil(s) secondary circuit
Timing reference signal and timing advance circuit
Spark plug and coil secondary wire radio interference
Engine misfire

7. Scan Tool Misfire Code
Means engine failed to ignite and burn air-fuel mixture properly
Indicates which engine cylinder is not producing combustion normally
Misfire can be caused by problems in
Ignition system
Fuel injection system
Emission control system
Engine itself

8. Spark Tester Spark intensity test or spark test Spark tester
Checks strength of electric arc produced by ignition system
Spark tester
Used to check ignition system output voltage

9. Spark Intensity Testing
Remove one of secondary wires from spark plug or from suspect direct ignition coil
Insert spark tester into wire or coil’s secondary conductor terminal
Ground spark tester by connecting alligator clip to good ground on engine or unibody (frame)
Crank or start engine and observe spark at tester’s air gap

10. Spark Test Results Strong spark Weak spark or no spark
Shows ignition system primary and secondary voltages are good
Shows ignition coil, pickup coil, electronic control unit, and other ignition system parts are functioning
Weak spark or no spark
Indicates something is wrong inside ignition circuit

11. Checking for a Dead Cylinder
Engine combustion chamber not igniting and burning fuel-air mixture on that cylinder’s power stroke
Symptoms include very rough idle and puffing noise at tailpipe

12. Checking for a Dead Cylinder (Cont.)
Pull off suspect cylinder’s ignition coil primary connector
On “live” or firing cylinder
Engine speed will drop and idle will become rougher
On dead cylinder
Idle smoothness and engine speed will not change

13. High-Voltage Leakage Test
Place hood cover over engine compartment to fully darken inspection area
Helps view any electric sparks on ignition components
Install vent hose
Chock wheels, put transmission in Park, and set emergency brake

14. High-Voltage Leakage Test (Cont.)
Start engine
Wear rubber gloves and eye protection
Look under hood cover for high-voltage leakage
Move primary and secondary conductors in their connectors
Watch for sparks jumping off components

15. High-Voltage Leakage Test (Cont.)
Ground non-powered test light and move it over secondary wires and conductors
Metal probe will attract any electrical leakage and glow
Replace any components that show leakage
If engine has direct ignition, remove each ignition coil to inspect high-voltage connection to spark plug

16. Ignition Primary Voltage Testing
Disconnect primary connector from one of ignition coils on engine
Install test jumper between harness and coil connectors
Connect high-impedance meter leads to bare metal conductors on jumper wires
Measure voltage applied to ignition coil with ignition switch in run position

17. Ignition Circuit Scope Testing
Oscilloscope or scope
Measures operating voltages of analog and digital signals
Often built into advanced scan tools
Uses a display screen
Shows changes in voltage over periods of time
(OTC)

18. Evaluating Ignition System Test Results
Evaluate results and narrow down possible causes
Use knowledge of system operation
Read service manual troubleshooting chart
Use Basic testing methods
Use common sense

19. Spark Plug Service Bad spark plugs cause many problems
Misfiring
Lack of engine power
Poor fuel economy
Exhaust odor
Hard starting
Test with oscilloscope or OBD II scanner
Will show up as abnormal waveforms or misfire code

20. Spark Plug Removal
Remove ignition coils, coil module, or spark plug wires
Use blow nozzle to clean off debris collected on top of engine
Remove screws securing direct ignition coils or coil module to engine
Wiggle coil or module while pulling it straight up

21. Spark Plug Removal (Cont.)
If spark plugs have wires, make sure they are numbered or located correctly in clips
Grasp spark plug wire by boot and pull to disconnect
Twist boot back and forth if stuck on plug
Again, blow debris from spark plug holes

22. Spark Plug Removal (Cont.)
Unscrew each spark plug using spark plug socket, extension, and ratchet
Lay each removed plug (in order) on fender cover or workbench
Do not mix up plugs
Inspect color and condition of electrodes to diagnose condition of engine and fuel system

23. Reading Spark Plugs
Closely inspect and analyze condition of tip and insulator
Properly burning plug should have brown to grayish-tan color
Black or wet plug indicates that it is not firing or problem in engine

24. Reading Spark Plugs (Cont.)
A—Properly burning plug, minimal deposits and grayish-tan color
B—Carbon-fouled plug from prolonged rich air-fuel mixture
C—High-mileage plug shows erosion at gap

25. Reading Spark Plugs (Cont.)
D—Oil-fouled plug, shiny and dark gray or black in color
E—Ash-fouled plug from burning low-quality gasoline
F—Physical damage on spark plug indicates internal engine failure

26. Gapping Spark Plugs
Set spark plug gap by spacing side electrode the correct distance from center electrode
Wire feeler gauge measures spark plug gap
Should drag lightly when pulled in and out

27. Installing Spark Plugs
Spark plugs set to correct gap are ready for installation
Use your fingers, spark plug socket, or short piece of vacuum hose to start plugs in their holes
After threading a few turns by hand
Turn them in with ratchet
Tighten spark plugs to specifications

28. Secondary Wire Service
Faulty secondary or spark plug wire
Burned or broken conductor
Deteriorated insulation
Resistance conductors can be easily damaged
Secondary wire insulation test
Checks for sparks arcing through insulation to ground

29. Secondary Wire Insulation Test
Darken shop or place fender covers over sides of vehicle’s hood
Start engine and visually inspect each wire for sparks of electric arcing leakage
Listen for popping or clicking sound

30. Secondary Wire Insulation Test (Cont.)
If arcing not evident during visual inspection
Move high-impedance test light or grounded screwdriver along length of each wire
Hold tip of tool about 1" from wire insulation
If arc jumps through insulation and onto test light probe or screwdriver, wire is bad and must be replaced

31. Secondary Wire Resistance Test
Remove each wire from its plug and from distributor cap or coil pack
Connect ohmmeter to each end of wire
Meter will measure wire’s internal resistance in ohms
Compare reading to specifications
(Chrysler)

32. Replacing Spark Plug Wires
Installing new spark plug wires is simple
Replace one by one
Compare length of old wire with length of new wire
Replace each wire with one of equal length
If all wires are removed at once, use engine firing order and cylinder numbers to route each wire correctly

33. Distributor Service Distributors are found on many older cars
Critical to proper operation of engine
Distributes high voltage to each spark plug wire
Controls ignition timing with changes in engine speed and load
If any part of distributor is faulty, engine performance suffers and emissions may increase

34. Distributor Cap and Rotor Service
Bad distributor cap or rotor can cause engine missing, backfiring, performance problems
Backfiring
Popping noise from throttle body or carburetor

35. Carbon Trace
Small, thin line of carbon-like substance that conducts electricity
Will short coil voltage to ground or to wrong plug wire
Can cause spark plugs to fire poorly, out of sequence, or not at all
When problems point to distributor cap or rotor troubles, check inside of cap for cracks and carbon traces

36. Replacing Distributor Cap and Rotor
Distributor caps secured either by screws or spring-type metal clips
Turn screws counterclockwise for removal
With spring clips, pry on top of clips carefully, do not crack cap
Wiggle and pull upward on cap to remove it from distributor body

37. Replacing Distributor Cap and Rotor (Cont.)
Rotors may be held by screws or press-fit onto distributor shaft
Pulling by hand will usually free press-fit rotor
If necessary, carefully pry under rotor
When installing distributor cap, notch or tab on cap must line up with distributor housing
Ensures that cap correctly aligns with rotor

38. Replacing Distributor Cap and Rotor (Cont.)
Before securing spring clips or screws
Push down on cap while twisting it from side to side
Make sure cap does not wobble on distributor
In some systems, ignition coil is housed inside distributor cap
Take coil out of old cap and install in new one

39. Electronic Ignition Service
Most electronic ignition distributors use pickup coil to sense trigger wheel rotation
Pickup coil sends small electrical impulses to ignition control module
If distributor fails to operate properly, ignition system can stop functioning

40. Testing Magnetic Pickup Coil
Connect ohmmeter or low-reading ac voltmeter across pickup coil output leads
Observe meter reading
Readings usually vary between 250 and 1,500 ohms
If using ac voltmeter, small ac voltage (3–8 volts) should be produced by magnetic pickup coil when engine is cranked
Check service manual for exact specifications

41. Testing Magnetic Pickup Coil (Cont.)
Wiggle wires to pickup coil while watching meter
Will help locate a break in leads
Lightly tap on coil with screwdriver handle
Could uncover any breaks in coil windings
If meter reading not within specifications, or readings change when leads move or coil is tapped, replace pickup coil

42. Testing Hall-Effect and Optical Sensors
Hall-effect and optical sensors tested in the same way as magnetic sensor
Check output signals and compare them to specifications
Often tested with scope to more accurately analyze output signals

43. Replacing Pickup Coil
Remove distributor cap, rotor, and screws holding coil to advance plate
Install procedures vary
Find detailed directions in service manual
Set air gap must after installing coil

44. Setting the Pickup Coil Air Gap
Position trigger wheel so one of its teeth points at pickup coil
Slide correct size nonmagnetic feeler gauge between pickup coil and trigger wheel tooth
Move pickup coil in or out until gauge fits snugly in gap
Tighten pickup screws and double-check air gap setting

45. Contact Point Distributor Service
Worn and burned contact points will cause high-speed missing, no-start problems, and many other ignition-related troubles
Faulty condenser may leak, be shorted, or be open
Leaking or open condenser will cause point arcing and burning
If shorted, primary current will flow to ground and engine will not start

46. Testing a Distributor Condenser
Test condenser with Ohmmeter
When connected, meter should register momentarily
As capacitor charges, reading should return to infinity

47. Replacing the Points and Condenser
Use small wrench to disconnect primary wires from points
Remove screws securing points to distributor
Use magnetic or clip-type screwdriver
Place small amount of grease on side of the breaker arm rubbing block
Fit points into distributor
Install point screws, condenser, and primary wires

48. Replacing the Points and Condenser (Cont.)
Point gap
Recommended distance between contacts in fully open position
With contacts point open
Slide specified feeler gauge between contacts
Adjust points using screwdriver or Allen wrench
Tighten hold-down screws
Recheck point gap

49. Using Tach-Dwell Meter
Measures engine speed
Measures contact point or ECM dwell
Measures resistance (sometimes)
Tach and dwell readings viewed with scan tool
Tachometer or tach
Measures engine speed by checking how often ignition coil(s) fires

50. Using Tach-Dwell Meter (Cont.)
Measures current flow as compared to degrees of engine crankshaft rotation
Dwell meter needed to work on antique and early muscle cars with contact-point or early electronic ignition systems

51. Fixed and Variable Dwell
Fixed dwell
Dwell time should remain the same at all speeds
Some vehicles can be set to fixed dwell for testing purposes
Variable dwell
Engine control module alters ignition coil dwell time with engine speed

52. Fixed and Variable Dwell (Cont.)
Current-limiting dwell
ECM sends high current through ignition coil windings until a strong magnetic field develops around windings
Saturated ignition coil
Reduces amount of current sent through coil windings

53. Ignition Timing Service
Proper ignition timing critical to engine performance
If ignition timing is incorrect, engine is not firing spark plugs at the right time
If ignition timing is off by even 1° of crankshaft rotation, fuel economy and power can drop considerably

54. Ignition Timing Service (Cont.)
Over-advanced ignition timing
Engine will suffer from spark knock or ping, caused by abnormal combustion
Retarded ignition timing
Engine will have poor fuel economy and lack power, especially during acceleration

55. Measuring Ignition Timing (Cont.)
OBD II vehicles
Scan tool displays ignition timing as live data so it can be compared to specifications
Older computer-controlled ignition systems must be put into base timing mode before timing is checked
Disconnect computer wiring harness
Or jumper specific pins on diagnostic connector

56. Measuring Ignition Timing (Cont.)
Dual-trace lab scope sometimes needed to check ignition timing
One scope lead connected to ignition coil primary
Another lead connected to crankshaft position sensor
Two waveforms can be compared to measure real-time timing advance or retard

57. Measuring Ignition Timing (Cont.)
On some older vehicles, use timing light to check timing
Timing light has three leads
Two small leads connect to battery
Larger lead connects to number one spark plug wire
Large lead may clip around plug wire
Some engines require magnetic pickup lead on timing light

58. Measuring Ignition Timing (Cont.)
Timing light flashes on and off
Start engine and shine timing light on timing marks
May be on front cover and harmonic balancer or on flywheel
Timing light will make the mark or marks appear to stand still
Allows you to properly measure timing

59. Measuring Ignition Timing (Cont.)
In older vehicles, rotating distributor housing in engine changes base ignition timing
Turning distributor housing against distributor shaft rotation advances timing
Turning housing with shaft rotation retards timing

60. Measuring Ignition Timing (Cont.)
In late-model vehicles
Ignition timing cannot be adjusted mechanically
If timing is incorrect, ECM or another component affecting timing must be replaced or updated

61. Measuring Ignition Timing (Cont.)
Today’s engines rely on multiple sensors to provide data for electronically adjusting ignition timing
Worn engine timing chain or stretched timing belt cause trouble codes and symptoms related to ignition timing and these sensors

62. Reprogramming ECM and Ignition Timing
Reprogramming ECM can change ignition timing curve with
Speed
Load
Engine temperature
Air temperature
Manufacturer sometimes provides software fixes

63. Ignition Coil (Coil Pack) Service
Faulty ignition coil may result in weak spark, intermittent spark, or no spark at all
Windings inside coil can break producing high resistance or opened coil circuit
If misfiring or dead cylinders correspond to one coil in coil pack, suspect coil pack

64. Testing Ignition Coils
Coil test may be needed when ignition system fails spark test
Since coil designs are different, testing procedures vary
Use ohmmeter to measure internal resistance of coil windings
Check resistance of both primary and secondary windings

65. Testing Ignition Coils (Cont.)
With coil pack, test windings of coil having spark problem
If number two cylinder is not firing, coil for that cylinder should be checked first
Normally, bad coil pack winding will show infinite resistance, or open

66. Replacing an Ignition Coil
To remove old coil
Disconnect wiring
Remove bolts securing old coil
Lift coil from engine
To install new coil
Bolt coil in place
Reconnect wires
Be careful not to connect coil in reverse polarity (backward)

67. Ignition Switch Service
Bad ignition switch can cause several problems
Engine may not crank or start
Engine may not shut off when ignition key is turned off
Starter may not disengage when ignition key is returned to run

68. Testing an Ignition Switch
Use test light to check ignition switch
Test light on start terminal
Light should glow only when key is turned to Start
In Run position
Light should glow when touched on Run terminal
In off position
Neither terminal should make test light glow

69. Replacing an Ignition Switch
Before removing dashboard-mounted switch, tumbler must be removed
Steering column-mounted ignition switch is separate from tumbler

70. Ignition Control Module Service
Faulty ignition control module can produce wide range of problems
Engine stalls when hot
Engine cranks but fails to start
Engine misses at high or low speeds
Ignition control module problems will show up after period of engine operation
Heat soaks into module and raises its temperature

71. Testing an Ignition Control Module
One of last components to test when troubleshooting ignition system
Unplug wires going to module and connect tester to module
Tester indicates if ignition control module fault exists

72. Heating the Ignition Control Module
Microscopic components inside ignition control module are very sensitive to high temperatures and vibration
Many technicians use heat gun or heat lamp bulb to warm unit
Simulates engine compartment temperature after engine has been running
Do not apply too much heat or it may be ruined

73. Replacing an Ignition Control Module
If control module is mounted in engine compartment or under dash
Carefully unplug wiring harness without damaging small terminal pins and plastic connectors
Unbolt and remove ignition or engine control module
Install new unit
Reconnect wiring harness

74. Replacing an Ignition Control Module (Cont.)
If ignition control unit is mounted inside distributor
Remove distributor cap
Disconnect wires leading to module
Remove screws holding module in place
Remove old control module
Install new unit according to service manual instructions

75. Replacing an Ignition Control Module (Cont.)
In many cases, bottom of ignition control module must be coated with special grease
This grease transfers heat into distributor housing
Protects module from overheating and circuit damage

76. Distributorless Ignition System Service
Many components used in a computer-controlled ignition system are similar to those found in older electronic or contact-point systems
Testing procedures for these parts covered earlier in this chapter
Computerized ignition system contains engine sensors and computer
Make it more difficult to troubleshoot and service

77. Replacing a Crankshaft Position Sensor
Most crankshaft position sensors simply lock into place and are not adjustable
Some require adjustment
Crankshaft position sensor air gap
Distance from tip of sensor to un-notched area on trigger wheel

78. Replacing a Crankshaft Position Sensor (Cont.)
To adjust crankshaft position sensor air gap
Loosen mounting screws holding sensor in place
Fit flat feeler gauge between one of the teeth on crank trigger wheel and sensor tip
Adjust sensor position so there is slight drag on feeler gauge
Tighten crank sensor mounting screws so they remain the correct distance from trigger wheel on crankshaft

79. Knock Sensor Service
Knock sensor used to detect abnormal combustion, or ping
When it “hears” pinging or knocking, sensor retards ignition timing or lowers turbo boost with turbo waste gate
Bad knock sensor can upset ignition timing and affect turbocharger boost pressure

80. Knock Sensor Service (Cont.)
To check knock sensor operation
Start engine
Allow it to reach operating temperature
Lightly tap on engine block or on bracket with wrench or small hammer
Simulates pinging or knocking
Should make computer retard ignition timing
If tapping has no effect, check sensor with VOM or scope

81. Direct Ignition System Service
Procedures for servicing direct ignition system are similar to those described for other types of ignition systems
Main difference is direct ignition system has a coil for each cylinder
Test like other ignition coils
Measure both primary and secondary winding resistance
Make sure primary voltage is getting to coil