| Topic group | Topic | Summary |
| Ignition systems | Basic ignition |
The ignition system ignites the fuel in the gasoline engine. There are three general types of ignition system: breaker ignition; electronic ignition; and direct ignition. |
| Ignition principles |
The ignition system provides a spark between the spark plug electrodes. The spark must occur at precisely the right time in the engine cycle, and it must have sufficient energy to bridge the gap and ignite the air-fuel mixture under all operating conditions. |
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| Ignition components |
The primary components of the automotive ignition system are: battery, spark plug, engine timing, distributor, spark intensifiers and high tension (HT) leads. |
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| Vacuum & centrifugal units |
For any given engine speed the correct spark timing varies according to: air/fuel ratio, octane rating, engine speed and engine load. |
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| Plug firing voltage |
The plug firing voltage needed to establish the spark is higher than the spark voltage needed to sustain the spark. |
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| Faraday's law | Induction coils operate according to Faraday's law in order to step up the nominal battery voltage to the voltage needed to bridge the gap across the spark plug electrodes. | |
| Contact breaker ignition | Contact breaker system | Contact breaker ignition systems provide a simple means of establishing and interrupting the current flowing in the primary ignition circuit. |
| Primary & secondary windings | The secondary winding, with about 100 times as many turns as the primary winding, can have an induced voltage about 100 times greater than the primary induced voltage. However, the actual firing voltage depends on many factors. |
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| The ballast resistor coil | A ballast resistor coil is designed to operate at approximately 7.5 volts and still provide the step-up transformer action needed, for secondary circuit operation. |
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| Dwell angle | The dwell angle in contact breaker systems determines the time allowed for current to flow through the primary winding and establish the necessary magnetic field. In electronic ignition systems the equivalent process is referred to as the primary circuit 'charging time'. |
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| Spark timing | The ignition timing point can be advanced by a centrifugal type mechanism according to engine speed and by a vacuum operated mechanism, according to load. |
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| Contact breaker components | Battery power source | A battery is used to supply a voltage to the system components. |
| Ballast resistor | The ballast resistor is used to reduce the voltage to the ignition coil during normal running conditions. |
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| Ignition coil | The ignition coil is a step-up transformer. It increases the battery voltage to provide a spark for ignition. |
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| Ignition switches |
The common points on an ignition switch include: Lock, Off (not on all vehicles); Accessories, On and Start. The key can only be removed from the 'Lock' position. |
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| Contact breaker | The contact breaker is a mechanically operated electrical switch in the primary ignition circuit. The contacts open and close automatically with engine rotation. |
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| Capacitor/condenser | A capacitor or condenser is used to assist in the rapid collapse of the magnetic field in the ignition coil. |
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| Distributors | The distributor in a contact breaker system distributes the high-tension voltage surges to the spark plugs in the correct sequence and at the correct instant in time in the engine cycle. |
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| Distributor types |
There are several different distributor types including: kettering system, pulse generator, hall effect generator, electronic and optical sensor unit. |
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| High-tension leads | High-tension leads are used to transmit the high voltage required by the spark plugs to ignite the fuel/air mixture in the cylinders. |
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| Spark plugs | Spark plugs deliver the spark that initiates combustion in an engine cylinder. They are identified by thread size or diameter, the reach or length of the thread, and by their heat range. |
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| Spark plug components |
The main spark plug components are a threaded metal case with a ceramic insulating covering, a sparking tip with an adjustable spark gap, center and side electrodes and a terminal to connect the plug to the ignition system. |
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| Advance & retard mechanisms | Ignition timing can be varied by a centrifugal advance mechanism, according to engine speed and by a vacuum advance unit according to engine load. |
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| Electronic systems & components | Induction | In electronic ignition systems the contact breaker is eliminated and the primary circuit is switched or triggered electronically. |
| Inductive system operation |
Low inductive ignition coils have a low number of primary turns and a low primary resistance. The ignition module limits maximum primary current to a safe value. |
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| Induction wiring |
Inductive type pulse generators use the principles of electro-magnetic induction to produce an AC voltage. This can be used to signal an ignition module to turn the primary circuit 'on' and 'off'. |
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| Hall effect sensors |
A Hall effect sensor provides voltage pulses that are generated by alternately shielding the sensor from a magnetic field, then exposing it. |
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| Hall effect operation |
Voltage pulses from a Hall generator can be used by an ignition module to control the operation of the primary circuit. |
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| Optical type sensors | Optical type sensors inside the distributor can be used to sense crank angle position. This information can be used by an engine management electronic control unit, to control ignition system operation. | |
| Distributorless systems | Distributorless ignition systems | In a waste spark system, each spark plug is fired by a high voltage impulse from an ignition coil shared with a companion cylinder. |
| Insulated coils |
In systems which employ an individual coil for each cylinder, the coils can be placed in an insulated cassette with each coil connected directly to its spark plug. |
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| Distributorless ignition system timing | Timing for the distributorless ignition system is controlled by an electronic control unit or ECU. Identification of each pair of cylinders is provided by a dual crank sensor attached to the engine timing cover. | |
| Ignition procedures | Checking ignition timing |
The objective of this procedure is to show you how to check ignition timing using a timing light. It is not necessary for the technician to alter the timing from the manufacturer's specifications. In some cases, serious damage could result. |
| Checking & changing a spark plug |
The objective of this procedure is to show you how to check and change a spark plug. The leads which come from the distributor must be removed from the spark plug in such a way that you can identify which cylinder they belong to. |
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| Removing & replacing contact points | The contact breaker points are normally found in the base of the distributor below the distributor cap and the rotor. The objective of this procedure is to show you how to remove and replace a vehicle's contact points. | |