All gasoline powered engines require a spark to ignite the mixture of gasoline and air. This spark must occur at the right time and in the correct cylinder. This is accomplished by the ignition system.
There are basically three types of ignition system used: the conventional breaker point typesystems that were used in vehicle from the early 1900s to the mid 1970s; the electronic systems; and the new distributor-less or wasted spark system that was introduced in the mid 80s and is still used today.
All ignition systems employ four basic components a battery to provide power for the system, a coil that is used to increase the voltage supplied by the battery from 12 volts to about 30,000 volts, a distributor that directs the high voltage to the right cylinder and a sparkplug that produces the spark that ignites the fuel mixture.
Point-type system:
In this type of ignition system, the battery power is fed through a resistor to the primary side of the coil and is then grounded through the closed ignition points in the distributor. Causing the current to flow through the primary, windings and creating an intense magnetic field.
As the distributor cam turns, the points are opened interrupting the flow of current causing the magnetic field to collapse. The collapse of the magnetic field causes the lines of force to cut through the secondary windings. Since the ratio of turns in the secondary windings is higher than the primary, the voltage is increased to about 30,000 volts.
The distributor rotor acts as a selector switch directing the high voltage created by the coil to the sparkplug in the proper cylinder where the spark causes the fuel mixture to ignite.
One of the major problems with this system was the points. Due to the arcing created by the points opening and closing the points would become burned which would render them useless after a while. Placing a condenser across the points would improve this condition but the points would still need to be replaced about every 10,000 miles.
In addition to the points the contacts on the rotor and cap would also become burned and would also need replacing.
Electronic systems:
In the 70s new emissions laws and the need for greater reliability created a need for a higher mileage, reduced emissions ignition system with greater reliability, which led to the development of the electronic ignition systems.
The major difference of the Electronic ignition system from the conventional ignition systems is the distributor components. Instead of a distributor cam, points, and condenser, the electronic ignition system has an armature, a pickup coil, and an electronic control module.
All electronic systems operate basically the same current flows from the battery through the ignition switch to the coils primary windings. The primary current is turned on and off as the armature revolves past the pickup. As each tooth of the armature nears the pickup coil, it creates a signal to the electronic module to turn off the flow of current to primary side of the coil. A timing circuit in the module will turn the current on again after the coils magnetic field has collapsed, which causes a high voltage in the secondary windings of the coil. The remainder of the system still operates the same as in a conventional ignition system.
In the electronic ignition systems the problem with the points has been solved but the rotor and cap still need to be replaced periodically.
Distributor-less systems:
The distributor-less ignition systems is not truly distributor-less, it just no longer has a mechanical distributor. It has been replaced by an electronic switching system.
There are two types of distributor-less systems, the true distributor-less system and the wasted spark system.
The distributor-less ignition has a dedicated coil for each cylinder. The timing of the spark is controlled by an Ignition Control Unit (ICU) and the Engine Control Unit (ECU).
The wasted spark system each cylinder is paired with the cylinder opposite it in the firing order. The ends of each coil secondary leads are attached to spark plugs for the paired opposites. These two plugs are on what is known as companion cylinders, cylinders that are at Top Dead Center (TDC) at the same time. But, they are paired opposites, because they are always at opposing ends of the 4 stroke engine cycle. When one is at TDC of the compression stroke, the other is at TDC of the exhaust stroke. When the coil discharges, both plugs fire at the same time.
The distributor-less ignition system has finally solved both of the reliability problems with the ignition system that has pledged automobile engines from the 1900s till the mid 80s. But there is still hope for older vehicles; as there are several very good aftermarket conversion kits available on the market at affordable prices.
