2. 34
Chapter
Ignition System Technology

3. Objectives After studying this chapter, you will be able to:
Explain the operating principles of any type of automotive ignition system.
Sketch the primary and secondary circuits of an ignition system.
Identify and describe the function of major ignition system components.

4. Objectives
Describe the purpose of secondary wires in an ignition system.
Compare ignition coil, spark plug, and ignition circuit variations.
Compare simple contact point systems with electronic ECM-controlled ignition systems.
Distinguish between distributorless and direct ignition systems.

5. Objectives Explain the need for accurate ignition timing control.
Describe the three basic methods used to control ignition system spark timing.
Correctly answer ASE certification test questions that require knowledge of ignition system theory and design.

6. Ignition System Fundamentals
Amplifies battery voltage or charging system voltage to over 40,000 volts, and delivers it to spark plugs
Gasoline engines use ignition system to initiate combustion on the power stroke
Diesels are compression ignition engines
Do not need ignition system to start combustion

7. Ignition System Fundamentals (Cont.)
Basic ignition system parts
Crankshaft position sensor
Primary wires
Ignition control module
Ignition coil
Spark plugs
Secondary wires
Ignition switch

8. Ignition System Operation
Ignition system supply voltage feeds to ignition system by battery or alternator
Battery provides electricity for starting engine
After engine is running, alternator supplies slightly higher voltage to battery and ignition system

9. Primary and Secondary Circuits
Primary circuit
All components and wires operating on low 12-volt dc from battery, alternator, or current from HV power control module
Secondary circuit
All parts carrying high-voltage current
Wires and parts between coil output windings and spark plug ground

10. Primary and Secondary Circuits (Cont.)
Secondary operating voltage of ignition system ranges from 4,000–100,000 volts, depending on system design

11. Ignition System Supply Voltage
Fed to ignition system by battery, alternator, or HV power control module
12-volt or HV battery provides electricity for starting engine
After engine is running, alternator or HV PCM supply slightly higher voltage

12. Bypass Circuit Bypass circuit
Used in older ignition systems to supply direct battery voltage to ignition system during starting

13. Resistance Circuit Special resistance wire Ballast resistor
Wire having internal resistance
Ballast resistor
Heat sensitive resistor that regulates voltage to ignition coil
Used in resistance circuit
Ensures relatively steady voltage of about 9.5–10.5 volts applied to ignition system

14. Secondary Wires Coil wire Spark plug wires
Carries high-voltage current from ignition coil to distributor cap
Spark plug wires
Carries coil voltage from distributor cap to spark plugs
Conductor is stranded metal wire
No longer used because they cause radio interference
Insulated boots fit over both ends to protect metal connectors

15. Secondary Wires (Cont.)
Resistance wires or radio suppression wires
Used for most secondary wire applications because they contain internal resistance, which helps prevent radio interference
(Champion Spark Plugs)

16. Spark Plugs Use ignition coil high voltage to ignite fuel mixture
Basic parts
Center terminal (center electrode)
Grounded side electrode
Ceramic insulator
Steel shell

17. Spark Plugs (Cont.) Spark plug reach Resistor spark plug
Distance between end of plug threads and seat or sealing surface on plug shell
Resistor spark plug
Internal resistance (around 10,000 ohms) to reduce static in radios and television sets
Non-resistor spark plug
Solid metal rod forming center electrode

18. Spark Plugs (Cont.) Spark plug gap Spark plug heat range
Distance between center and side electrodes
Normal gap specifications range from 0.030"–0.080" (0.76 mm–2.0 mm)
Spark plug heat range
Rating of spark plug tip’s operating temperature

19. Spark Plugs (Cont.) Hot spark plug Cold spark plug
Long insulator tip and tends to burn off deposits
Cold spark plug
Shorter insulator tip
Operates at cooler temperature
Used in engines that operate at high speeds

20. Spark Plugs (Cont.)
(Chrysler)

21. Ignition Coils Ignition coil Ignition coil open-circuit voltage
Pulse-type transformer that produces short bursts of high voltage to start combustion
Ignition coil open-circuit voltage
Maximum voltage potential
Ranges from 40,000–100,000 volts in late-model designs

22. Ignition Coils (Cont.) Two primary terminals Iron core
High-voltage terminal
Primary windings
Several hundred turns of heavy wire
Secondary windings
Several thousand turns of very fine wire
(Chrysler)

23. Ignition Coil Operation
Current flows through primary windings creating a strong magnetic field
Iron core concentrates and strengthens this field
When current is interrupted, magnetic field collapses
Secondary windings have more turns than primary windings
Up to 60,000 volts induced

24. Ignition Coil Operation (Cont.)
High voltage shoots out of high-voltage terminal
Traveling through secondary circuit to spark plug
(Saab)

25. Ignition Coil Designs Coil pack Waste-spark ignition coil
Several ignition coils combined into one assembly
Used in distributorless ignition systems
Waste-spark ignition coil
Wired so it fires two spark plugs at the same time
Direct ignition coil
Bolts directly over top of spark plug on top of engine
Fires only on power strokes for maximum efficiency

26. Distributorless Ignition System
Also called computer-coil ignition
Crankshaft-triggered ignition system
Multiple ignition coils
Coil control unit
Engine sensors
Computer (engine control module)
Operate sparks plugs
Distributor not needed in this type of system

27. Distributorless Ignition System (Cont.)
Electronic coil module
Consists of two or more ignition coils and coil control unit
Each coil in module serves two cylinders

28. Distributorless Ignition System (Cont.)

29. Distributorless Ignition System Operation

30. Direct Ignition System
One coil assembly mounted directly above each spark plug
Eliminates need for spark plug wires
Allows use of smaller ignition coils
Other components in direct ignition system are the same as those in distributorless system

31. Direct Ignition System (Cont.)
Ionization knock sensing system
Detects abnormal combustion and knocking
Dual spark plug ignition system
Two spark plugs used in each cylinder
Multiple discharge ignition system
Fires spark plugs more than once during each power stroke

32. Distributor Ignition Systems
Used in older ignition systems
Actuates on/off cycles of current flow through ignition coil primary windings
It causes spark to occur at each plug earlier in compression stroke as engine speed increases and vice versa
It changes spark timing with changes in engine load

33. Distributor Ignition Systems (Cont.)
Sometimes, bottom of distributor shaft powers engine oil pump
Some distributors house ignition coil and electronic switching circuit in one assembly
Unitized distributors

34. Distributor Ignition Systems (Cont.)
Distributor types
Contact point distributor
Pickup coil distributor
Hall-effect distributor
Optical distributor
Distributor drive
Refers to method used to rotate distributor shaft to match engine rpm

35. Contact Point Ignition Systems
Contact point distributor major parts
Distributor cam
Contact points (breaker points)
Condenser (capacitor)
Point dwell or cam angle
Amount of time contact points remain closed between each opening
Point gap
Distance between fully open contact points

36. Contact Point Ignition Systems (Cont.)
(Deere & Co.)

37. Point Dwell
Amount of time contact points remain closed between each opening
Without enough point dwell, a weak spark would be produced
(Echlin)

38. Electronic Ignition System
Also called solid-state system or transistor ignition system
Uses ignition control module and either distributor pickup coil, Hall-effect device, or optical pickup to operate ignition coil
More dependable than contact point system
No mechanical breakers to wear or burn

39. Pickup Coil Also called sensor assembly or sensor coil
Produces tiny voltage pulses that are sent to ignition control module
Trigger wheel
Also called reluctor or pole piece
Fastened to upper end of distributor shaft
Replaces distributor cam
Has one tooth for each engine cylinder

40. Pickup Coil (Cont.)

41. Hall-Effect Pickup Solid-state chip or module
Produces electrical signal when triggered by slotted wheel
Constant amount of current sent through device
Permanent magnet located next to Hall-effect chip
(Ford)

42. Optical Pickup
Slotted rotor plate rotates between LEDs and photo diodes
When slot passes, light from LED strikes photo diode
Electrical signal is generated
(Nissan)

43. Ignition Control Modules
“Electronic switch”
Turns ignition coil primary current on and off
Module does same thing as opening and closing contact points

44. Crankshaft-Triggered Ignition
Can maintain more precise ignition timing than system with distributor-mounted pickup
Crankshaft trigger wheel
Also called pulse ring or reluctor ring
Provides engine speed and crankshaft position data for sensors and computer
Performs same function as trigger wheel in electronic ignition’s distributor

45. Crankshaft-Triggered Ignition (Cont.)
(Robert Bosch)

46. Engine Firing Order
Sequence in which spark plugs fire to cause combustion in each cylinder
Firing order information used when
Installing plug wires
Checking ignition timing
(Mitchell Manuals and Echlin)

47. Ignition Timing Ignition timing or called spark timing Timing advance
How early or late spark plugs fire in relation to engine pistons’ position
Timing advance
Occurs when spark plugs fire sooner during engine’s compression strokes
Timing retard
Occurs when spark plugs fire later during compression strokes

48. Ignition Timing (Cont.)
Three basic methods to control ignition system spark timing
Electronic advance
Distributor centrifugal advance
Distributor vacuum advance

49. Electronic (Computer) Spark Advance
Engine sensors, ignition control module, and computer adjusts ignition timing
Engine sensors
Check various operating conditions
Send data to computer
Computer analyzes data
Changes timing for maximum efficiency

50. Electronic Spark Advance (Cont.)
Sensors that influence ignition timing
Crankshaft position sensor
Camshaft position sensor
Manifold absolute pressure sensor
Intake air temperature sensor
Engine coolant temperature sensor
Knock sensor
Throttle position sensor

51. Distributor Centrifugal and Vacuum Advance
Distributor centrifugal advance
Ignition coil and spark plugs fire sooner as engine speed increases
Distributor vacuum advance
Additional spark advance at part throttle positions when engine load is low
(Robert Bosch)

52. Base Ignition Timing
All late-model cars use computers to control ignition timing advance
To check timing, may have to trigger computer to go to base timing
Base timing is ignition timing without computer controlled advance