1. Chapter 26
Ignition Systems

2. Ignition Systems Part of the computerized engine control system
Three basic types
Distributor-based
Distributorless
Direct ignition

3. Purposes of the Ignition System
It must generate spark with enough heat to ignite the air/fuel mixture
It must maintain the spark long enough to allow for complete combustion
It must deliver the spark so combustion can begin at the precise time

4. Basic Circuitry - Primary
Battery
Ignition switch
Ballast resistor (older systems)
Ignition coil primary winding
Triggering device
Switching device or control module

5. Basic Circuitry - Secondary
Ignition coil secondary winding
Distributor cap and rotor (DI systems)
High-voltage cables
Spark plugs

6. Primary Circuit Operation
Ignition switch on
Current flows into primary coil winding
A primary switching device stops current flow through the coil
This causes the magnetic field to collapse

8. Secondary Circuit Components
Ignition coil secondary winding
Distributor cap and rotor (DI systems)
Spark plug cables (some systems)
Spark plugs

9. DI Secondary Circuit

10. Secondary Circuit Operation
Collapse of the magnetic field in the primary induces high voltage into the coil secondary
This voltage is used to establish a complete circuit so current can flow
The excess energy is used to maintain the current flow across the spark plug gap

11. Knowledge Check
Which of the following is NOT part of the primary circuit?
A. Ignition switch
B. Primary coil winding
C. Spark plug
D. Switching device
C – Spark plug

12. EI Systems
May have a single coil for each cylinder or two cylinders may share a coil
The ignition module controls firing order and spark timing
Additional energy is released as current flow
This allows higher firing current and longer firing times, 1.5 ms compared to DI’s 1 ms

13. Coil at Plug Secondary Circuit

14. DIS Secondary Circuit

15. Ignition Coils Coils are pulse transformers
Output dependant upon the number of windings and current flow
CEMF increases time to become fully saturated
Dwell is the period of current flow

17. Ignition Coils (Cont.) Typical coil requires 2-6 ms to be saturated
Dwell period and primary current are controlled

18. Secondary Voltage
Typical voltage requirement to jump the plug gap is 10,000 volts
Most coils have at least 25,000 volts available – called secondary reserve voltage
Reserve necessary to compensate for high cylinder pressures

19. Spark Jumping the Gap

20. Spark Plugs Provides the air gap Resistor reduces RFI
Standard plug electrodes are copper
Platinum and iridium electrodes extend plug life

21. Platinum tipped spark plug

22. Spark Plug Reach
Reach is critical for proper gap placement

23. Heat Range Heat must be dissipated quickly
Heat travels from the electrode through the insulator to the cylinder head

24. Spark Plug Gaps Correct gap is necessary for proper operation
Too wide can cause misfiring
Too narrow can cause fouling and misfires

25. Electrodes May be made of copper, platinum, iridium, or yttrium
Various styles of positive and ground electrodes in use

26. Ignition Cables Carry high voltage to spark plugs
Carbon fiber core acts as a resistor
Reduces RFI and increases firing voltage
Reduces plug wear by reducing current

28. Knowledge Check Which is not a common spark plug electrode material?
A. Copper
B. Yttrium
C. Nickel
D. Platinum
C – Nickel

29. Triggering and Switching Devices
A triggering device monitors crankshaft position

30. Triggering and Switching Devices (Cont.)
A switching device controls current flow through the coil primary winding
Electronic switching components are part of an ignition control module or the PCM

31. Engine Position Sensors
Magnetic Pulse Generator
Consists of a reluctor and pickup coil
Metal Detection Sensor
The electromagnet is in the pickup coil
Hall-effect Sensor
Produces a square wave signal
Is most commonly used
Magnetoresistive Sensor
Looks like a magnetic sensor but outputs a signal like a Hall-effect
Photoelectric Sensor
Uses an LED and moving slotted disc

36. DI System Operation
The camshaft drives the distributor at one-half crankshaft speed
The position sensor triggers the switching device
The coil is triggered by the switching device

37. Distributor May contain pick up assembly, ignition module, and coil
Rotor sits on top of distributor shaft and spins inside of distributor cap

38. Electronic Ignition Systems
No moving parts
Cylinders individually controlled
Flexible mounting locations
Less radio frequency interference
No timing adjustments
More time for coil saturation

39. Double-Ended Coil or Waste Spark Systems
One coil fires two plugs
These are the companion cylinders
One plug fires positive to negative
The other fires negative to positive

40. Coil-Per-Cylinder Ignition
Coil-on-plug and coil-near-plug
Allows for more time between firings and increased saturation time
A single coil failure affects only one cylinder
COP require adaptors or plug wires to connect an ignition scope

42. Twin Spark Plug Systems
One plug on intake side of combustion chamber and one on exhaust side
Results in cleaner combustion

43. EI System Operation
Biggest differences are in number of coils and the use of CKT and CMP sensors
Layout and operation of the sensors are designed to provide fast engine starts and synchronization of the fuel and ignition systems

44. Hall-Effect Sensors

45. Magnetic Pulse Generators

46. Knowledge Check
Technician A says a waste-spark system uses one coil per plug. Technician B says a waste-spark system fires one plug positive to negative and the other plug negative to positive. Who is correct?
Technician B

47. Misfire Detection The CKP identifies which cylinder
Detected by variation in crank speed
PCM uses wheel speed data to determine if crank speed variation is from rough road conditions or misfire

49. Basic Timing The PCM controls timing and is not adjustable
Timing is fixed during cranking
Once a certain engine speed is reached, the PCM adjusts timing
Timing inputs include RPM, load, throttle position, and coolant temperature

50. Timing Retard and Advance
Timing controlled by ignition module
Older systems used mechanical and vacuum systems

51. Timing Corrections Temperature Engine Knock Stabilizing Idle
Advanced with low coolant temperature
Engine Knock
Timing retarded when knock is detected
Stabilizing Idle
Used if desired idle speed is not correct

52. Timing Corrections (Cont.)
EGR
Advanced when EGR is opened
Transition Correction
During rapid acceleration/decelerations
Torque Control
To smooth automatic transmission shifting
Traction Control
Reduces engine torque by retarding timing