Ignition System Components and Operation

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Chapter 19
Ignition System Components and Operation

• CHAPTER OBJECTIVES
• Explain how ignition coils create 40,000 volts.
• Discuss crankshaft position sensor and pickup
  coil operation.
• Describe the operation of waste-spark or
  coil-on-plug ignition systems.

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• Ignition System Operation
• The ignition system includes components and
  wiring necessary to create and distribute a high
  voltage (up to 40,000 volts or more).
• All ignition systems apply voltage close to
  battery voltage to the positive side of the
  ignition coil and pulse the negative side to
  ground.
• When the coil negative lead is grounded, the
  primary (low-voltage) circuit of the coil is
  complete and a magnetic field is created by the
  coil windings.

3

• Ignition System Operation (continued)
• When the circuit is opened, the magnetic field
  collapses and induces a high-voltage spark from
  the secondary winding of the ignition coil.
• Distributor ignition (DI) is the term specified
  by the Society of Automotive Engineers (SAE) for
  an ignition system that uses a distributor.
• Electronic ignition (EI) is the term specified by
  the SAE for an ignition system that does not use
  a distributor.

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Ignition System Components and Operation

• Ignition Coils
• The coil creates a high-voltage spark by
  electromagnetic induction.
• Many ignition coils contain two separate but
  electrically connected windings of copper wire.
• Other coils are true transformers in which the
  primary and secondary windings are not
  electrically connected.

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• Ignition Coils (continued)
• The center of an ignition coil contains a core of
  laminated soft iron (thin strips of soft iron).
• This core increases the magnetic strength of the
  coil.
• Surrounding the laminated core are approximately
  20,000 turns of fine wire (approximately 42
  gauge).
• These windings are called the secondary coil
  windings.
• Surrounding the secondary windings are
  approximately 150 turns of heavy wire
  (approximately 21 gauge).
• These windings are called the primary coil
  windings.

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• Ignition Coils (continued)
• The secondary winding has about 100 times the
  number of turns of the primary winding, referred
  to as the turn ratio (approximately 1001).
• The primary windings of the coil extend through
  the case of the coil and are labeled as positive
  and negative.
• The positive terminal of the coil attaches to the
  ignition switch, which supplies current from the
  positive battery terminal.
• The negative terminal is attached to an
  electronic ignition module (or igniter), which
  opens and closes the primary ignition circuit by
  opening or closing the ground return path of the
  circuit.

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• Mutual Induction
• In an ignition coil there are two windings, a
  primary and a secondary winding.
• When a change occurs in the magnetic field of one
  coil winding, a change also occurs in the other
  coil winding.
• Therefore, if the current is stopped from flowing
  (circuit is opened), the collapsing magnetic
  field cuts across the turns of the secondary
  winding and creates a high voltage in the
  secondary winding.
• This generation of an electric current in both
  coil windings is called mutual induction.
• The collapsing magnetic field also creates a
  voltage of up to 250 volts in the primary
  winding.

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• How Ignition Coils Create 40,000 Volts
• If the primary circuit is completed, current
  (approximately 2 to 6 A) can flow through the
  primary coil windings.
• This flow creates a strong magnetic field inside
  the coil.
• When the primary coil winding ground return path
  connection is opened, the magnetic field
  collapses and induces a voltage of from 250 to
  400 volts in the primary winding of the coil and
  a high-voltage (20,000 to 40,000 volts)
  low-amperage (20 to 80 mA) current in the
  secondary coil windings.
• This high-voltage pulse flows through the coil
  wire (if the vehicle is so equipped), distributor
  cap, rotor, and spark plug wires to the spark
  plugs.

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• Primary Ignition Circuit
• Battery
• Ignition switch
• Primary windings of coil
• Pickup coil (crank sensor)
• Ignition module (igniter)
• Secondary Ignition Circuit
• Secondary windings of coil
• Distributor cap and rotor (if the vehicle is so
  equipped)
• Spark plug wires
• Spark plugs

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• Married And Divorced Coil Design
• An ignition coil contains two windings a
  primary winding and a secondary winding and these
  windings can be either connected together or kept
  separated.
• Divorced. These are also called a true
  transformer design and used by most waste spark
  ignition coils to keep both the primary and
  secondary winding separated.

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• Primary Circuit Operation
• To get a spark out of an ignition coil, the
  primary coil circuit must be turned on and off.
• This primary circuit current is controlled by a
  transistor (electronic switch) inside the
  ignition module or (igniter) that in turn is
  controlled by one of several devices, including
• Pickup coil (pulse generator)
• The magnetic pulse generator is installed in the
  distributor housing.
• The pulse generator consists of a trigger wheel
  (reluctor) and a pickup coil.
• The pickup coil consists of an iron core wrapped
  with fine wire, in a coil at one end and attached
  to a permanent magnet at the other end.

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• Primary Circuit Operation (continued)
• Pickup coil (pulse generator) (continued)
• The center of the coil is called the pole piece.
• The pickup coil signal triggers the transistor
  inside the module and is also used by the
  computer for piston position information and
  engine speed (RPM).

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• Primary Circuit Operation (continued)
• Pickup coil (pulse generator) (continued)

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• Primary Circuit Operation (continued)
• Hall-effect switch
• This switch also uses a stationary sensor and
  rotating trigger wheel (shutter).

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• Primary Circuit Operation (continued)
• Hall-effect switch (continued)
• Hall-effect is the ability to generate a voltage
  signal in semiconductor material (gallium
  arsenate crystal) by passing current through it
  in one direction and applying a magnetic field to
  it at a right angle to its surface.
• Most Hall-effect switches in distributors have a
  Hall element or device, a permanent magnet, and a
  rotating ring of metal blades (shutters) similar
  to a trigger wheel (another method uses a
  stationary sensor with a rotating magnet.)
• When the shutter blade enters the gap between the
  magnet and the Hall element, it creates a
  magnetic shunt that changes the field strength
  through the Hall element.

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• Primary Circuit Operation (continued)
• Hall-effect switch (continued)

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• Primary Circuit Operation (continued)
• Magnetic crankshaft position sensors
• This sensor uses the changing strength of the
  magnetic field surrounding a coil of wire to
  signal the module and computer.
• This signal is used by the electronics in the
  module and computer as to piston position and
  engine speed (RPM).

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• Primary Circuit Operation (continued)
• Optical sensors
• These use light from a LED and a phototransistor
  to signal the computer.
• An interrupter disc between the LED and the
  phototransistor has slits that allow the light
  from the LED to trigger the phototransistor on
  the other side of the disc.

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• Primary Circuit Operation (continued)
• Optical sensors (continued)
• Most optical sensors (usually located inside the
  distributor) use two rows of slits to provide
  individual cylinder recognition (low-resolution)
  and precise distributor angle recognition
  (high-resolution) signals.

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• Distributor Ignition (continued)
• DaimlerChrysler Distributor Ignition (continued)
• The pickup coil in the distributor (pulse
  generator) generates the signal to open and close
  the primary coil circuit.

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• Waste-Spark Ignition Systems
• Each coil is a true transformer in which the
  primary winding and secondary winding are not
  electrically connected.
• Each end of the secondary winding is connected to
  a cylinder exactly opposite the other in the
  firing order, which is called a paired cylinder.

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• Waste-Spark Ignition Systems (continued)
• This means that both spark plugs fire at the same
  time.
• When one cylinder (for example, 6) is on the
  compression stroke, the other cylinder (3) is on
  the exhaust stroke.
• This spark that occurs on the exhaust stroke is
  called the waste spark, because it does no useful
  work and is only used as a ground path for the
  secondary winding of the ignition coil.
• The voltage required to jump the spark plug gap
  on cylinder 3 (the exhaust stroke) is only 2 to 3
  kV and provides the ground circuit for the
  secondary coil circuit.
• The remaining coil energy is used by the cylinder
  on the compression stroke.
• One spark plug of each pair fires straight
  polarity and the other cylinder fires reverse
  polarity.

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• Ignition Control Circuits
• Ignition control (IC) is the OBD-II terminology
  for the output signal from the PCM to the
  ignition system that controls engine timing.
• Ford referred to this signal as spark output
  (Spout) and General Motors referred to this
  signal as electronic spark timing (EST).
• This signal is now referred to as the ignition
  control (IC) signal.

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• Ignition Control Circuits (continued)
• The ignition control signal is usually a digital
  output that is sent to the ignition system as a
  timing signal.
• If the ignition system is equipped with an
  ignition module, then this signal is used by the
  ignition module to vary the timing as engine
  speed and load changes.
• If the PCM directly controls the coils, such as
  most coil-on-plug ignition systems, then this IC
  signal directly controls the coil primary and
  there is a separate IC signal for each ignition
  coil.

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• Bypass Ignition Control
• A bypass-type of ignition control means that the
  engine starts using the ignition module for
  timing control and then switches to the PCM for
  timing control after the engine starts.
• A bypass ignition is commonly used on General
  Motors engines equipped with distributor ignition
  (DI), as well as those equipped with waste-spark
  ignition.

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• Bypass Ignition Control (continued)
• The bypass circuit includes four wires
• Tach reference (purple/white). This wire comes
  from the ignition control (IC) module and is used
  by the PCM as engine speed information.
• Ground (black/white). This ground wire is used
  to ensure that both the PCM and the ignition
  control module share the same ground.

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• Bypass Ignition Control (continued)
• Bypass (tan/black). This wire is used to conduct
  a 5-volt DC signal from the PCM to the ignition
  control module to switch the timing control from
  the module to the PCM.
• EST (ignition control) (white wire). This is the
  ignition timing control signal from the PCM to
  the ignition control module.

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• Diagnosing A Bypass Ignition System
• One advantage of a bypass-type of ignition is
  that the engine will run without the computer
  because the module can do the coil switching and
  can, through electronic circuits inside the
  module, provide for some spark advance as the
  engine speed increases.
• This is a safety feature that helps protect the
  catalytic converter if the ignition control from
  the PCM is lost.

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• Up-Integrated Ignition Control
• Most coil-on-plug and many waste-spark-type
  ignition systems use the PCM for ignition timing
  control.
• This type of ignition control is called
  up-integrated because all timing functions are
  interpreted in the PCM, rather than being split
  between the ignition control module and the PCM.
• The ignition module, if even used, contains the
  power transistor for coil switching.
• The signal, as to when the coil fires, is
  determined and controlled from the PCM.

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• Compression Sensing Ignition
• Some waste spark ignition systems, such as those
  used on Saturns, use the voltage required to fire
  the cylinders to determine cylinder position.
• It requires a higher voltage to fire a spark plug
  under compression than it does when the spark
  plug is being fired on the exhaust stroke.
• The electronics in the coil and the PCM can
  detect which of the two cylinders that are fired
  at the same time requires the higher voltage,
  which indicates the cylinder on the compression
  stroke.
• Engines equipped with compression sensing
  ignition systems, such as Saturns , do not
  require the use of a camshaft position sensor to
  determine cylinder number.

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• Coil-On-Plug Ignition
• Coil-on-plug (COP) ignition uses one ignition
  coil for each spark plug.
• This system is also called coil-by-plug,
  coil-near-plug, or coil-over-plug ignition.

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• Coil-On-Plug Ignition (continued)
• There are two basic types of coil-on-plug
  ignition including
• 2-wire
• This design uses the vehicle computer to control
  the firing of the ignition coil.
• The two wires include ignition voltage feed and
  the pulse ground wire, which is controlled by the
  computer.
• All ignition timing and dwell control are handled
  by the computer.

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• Coil-On-Plug Ignition (continued)
• 3-wire
• This design includes an ignition module at each
  coil.
• The three wires include
• Ignition voltage
• Ground
• Pulse from the computer to the built-in module

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• Ignition Timing
• Ignition timing refers to when the spark plug
  fires in relation to piston position.
• The ignition in the cylinder takes a certain
  amount of time usually 30 ms (3/1000 of a
  second).
• For maximum efficiency from the expanding gases
  inside the combustion chamber, the burning of the
  air-fuel mixture should end by about 10 after
  top dead center.

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• Ignition Timing (continued)
• If the burning of the mixture is still occurring
  after that point, the expanding gases do not
  exert much force on the piston because it is
  moving away from the gases.
• Therefore, to achieve the goal of having the
  air-fuel mixture by completely burned by the time
  the piston reaches 10 after top dead center
  (ATDC), the spark must be advanced (occur sooner)
  as the engine speed increases.

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• Knock Sensors
• Knock sensors are used to detect abnormal
  combustion often called ping, spark knock, or
  detonation.
• Whenever abnormal combustion occurs, a rapid
  pressure increase occurs in the cylinder,
  creating a noise.
• Inside the knock sensor is a piezoelectric
  element that generates a voltage when pressure or
  a vibration is applied to the unit.
• The voltage signal from the knock sensor (KS) is
  sent to the PCM.
• The PCM retards the ignition timing until the
  knocking stops.

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• Diagnosing The Knock Sensor
• A scan tool can be used to check the operation of
  the knock sensor, using the following procedure.
• Step 1
• Start the engine and connect a scan tool to
  monitor ignition timing and/or knock sensor
  activity.
• Step 2
• Create a simulated engine knocking sound by
  tapping on the engine block or cylinder head with
  a soft faced mallet.

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• Diagnosing The Knock Sensor (continued)
• Step 3
• Observe the scan tool display.
• The vibration from the tapping should have been
  interpreted by the knock sensor as a knock,
  resulting in a knock sensor signal and a
  reduction in the spark advance.
• A knock sensor can also be tested using a digital
  storage oscilloscope.

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Diagnosing The Knock Sensor (continued)
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• Spark Plugs
• Spark plugs are manufactured from ceramic
  insulators inside a steel shell.
• The threads of the shell are rolled and a seat is
  formed to create a gas-tight seal with the
  cylinder head.

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• Spark Plugs (continued)
• The physical difference in spark plugs includes
• Reach. This is the length of the threaded part
  of the plug.
• Heat range. The heat range of the spark plug
  refers to how rapidly the heat created at the tip
  is transferred to the cylinder head. A plug with
  a long ceramic insulator path will run hotter at
  the tip than a spark plug that has a shorter
  path.
• Type of seat. Some spark plugs use a gasket and
  others rely on a tapered seat to seal.