Welcome To,Ignition System Operation & Diagnosis,SECTION 4,Objectives,Describe the three major functions of an ignition system. Name the operating conditions of an engine that affect ignition timing. Name the two major electrical circuits used in ignition systems and their common components. Describe the operation of ignition coils, spark plugs, and ignition cables.,continued,Objectives,Explain how high voltage is induced in the coil secondary winding. Describe the various types of spark timing systems, including electronic switching systems and their related engine position sensors. Explain the basic operation of a computer-controlled ignition system.,continued,Objectives,Explain how the fuel injection system may rely on components of the ignition system. Describe the operation of distributor-based ignition systems. Describe the operation of distributorless ignition systems.,continued,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.,continued,Factors That Affect Timing,Engine speed (rpm) At higher rpms, the crankshaft turns through more degrees in a given period of time. If combustion is to be completed by 10 ATDC, ignition timing must occur sooner or be advanced.,continued,Factors That Affect Timing,continued,Factors That Affect Timing,Engine load Under light loads a high vacuum or low pressure exists and less air/fuel mixture drawn into the cylinders producing less combustion pressure and combustion time is slow. To complete combustion by 10 ATDC, ignition timing must be advanced. Under heavy loads, the vacuum is low and a larger mass of air/fuel mixture can be drawn in. High combustion pressure and rapid burning results and the ignition timing must be retarded to prevent complete burning before 10 ATDC.,continued,Factors That Affect Timing,Firing order Examples of typical firing orders,continued,Ignition System,Primary Circuit Components Battery Ignition switch Ballast resistor (older systems) Ignition coil primary winding Triggering device Switching device or control module,continued,Ignition System,Primary circuit operation Battery current flows through the ignition switch and the primary winding of the ignition coil, through some type of switching device and back to ground creating a magnetic field. The switching device or control module interrupts this current flow at predetermined times causing When it does, the magnetic field in the primary winding collapses generating a high-voltage surge in the secondary winding of the ignition coil.,continued,Ignition System,Secondary Circuit Components Ignition coil secondary winding Distributor cap and rotor (DI systems) Spark plug cables (some systems) Spark plugs,continued,Ignition System,Secondary circuit operation (Distributor ignition - DI) High-voltage from the secondary winding passes through an ignition cable running from the coil to the distributor and in to the rotor. The rotor then distributes the high voltage to the individual spark plugs through a set of ignition cables that are arranged in the distributor cap according to the engine firing order.,continued,Ignition System,Secondary circuit operation (Distributorless ignition - EI) EI systems have no distributor; spark distribution, firing order, spark timing and advance is controlled by an electronic control unit and/or the vehicles computer. Instead of a single ignition coil for all cylinders, each cylinder may have its own ignition coil, or 2 cylinders may share one coil. The coils are wired directly to the spark plug they control.,continued,Primary and Secondary Circuits,continued,Types of Ignition Systems,Distributor (DI) systems The voltage produced by the coil is sent to the distributor. The spark is delivered to the cylinders through the rotor and distributor cap. Distributorless (EI) systems Have multiple coils that deliver the spark to each cylinder.,continued,Ignition System Components,Ignition coil The primary coil is normally composed of 100 to 200 turns of 20-gauge wire. When a current is passing through the primary coil, it magnetizes the iron core. The strength of the magnet depends directly on the number of wire loops and the amount of current flowing through those loops. The secondary coil consist of 15 000 to 25 000, or more, turns of very fine copper wire.,continued,Ignition System Components,Ignition coil (cont) When the primary coil circuit is suddenly opened, the magnetic field instantly collapses. The sudden collapsing of the magnetic field produces a very high voltage in the secondary windings. This high voltage is used to push current across the gap of the spark plug.,continued,Ignition System Components,Ignition coil Current passing through the coils primary winding creates magnetic lines of force that cut across and i