Before electronic ignition systems were developed, ignition control of an engine was undertaken using mechanical distributors. In distributor-based systems, the distributor directs the output from a single high-tension (HT) ignition coil to the relevant spark plug. Control over the timing of ignition is done through a cam operated contact breaker, centrifugal weights, springs and cams, with ‘load mapping' done through using a vacuum advance unit.

These distributor-based systems are prone to mechanical wear, insulation break down and contact failure. To keep the ignition timing correct these systems require a periodic ‘tune up' to keep them working correctly.

Modern electronic ignition

systems do not require a distributor. A single small HT coil is used for each spark plug and the igniter operates each coil separately in the correct sequence.

Engine position information is provided by engine position sensors

and a timing disks that are accurately attached to one or two of the main engine shafts, such as the camshaft. The firing sequence and variable spark advance is computed accurately from the pattern of teeth or pegs on the timing disk. If load mapping is required, this can be achieved by adding a manifold pressure sensor or a throttle angle potentiometer to the system. A variety of extra features are available on such systems, which can be accessed and adjusted by a PC.

The main advantages of electronic ignition systems:
Electronic Ignition systems

provide extremely accurate spark timings, leading to improved combustion and emissions control. As there is no mechanical contact there is no wear therefore the accuracy is maintained. These reasons are why electronic ignition is used as standard throughout the industry.