The ignition system for the internal combustion engine creates a spark that ignites the fuel-air mixture in the engine's cylinders. It must do this exactly at the correct time at several times per minute for each cylinder of the engine. Modern engines use a direct fire ignition system.
The direct fire ignition system fires the spark plugs directly from the ignition coil, instead of the distributor cap, or rotor. The system is also known as the distributorless ignition system and it became available in the late 1980s.
The direct fire ignition system is completely controlled by the car's onboard computer. It is completely a solid state electronic system and uses no moving parts. Direct fire ignitions are maintenance-free, except for the changing of spark plugs. That occurs at 60,000- to 100,000-mile intervals. This improves the reliability of the direct fire system over the distributor ignition system.
The ignition coils of the direct fire ignition system serve two spark plugs. Multiple coils replace the distributor. The coil fires two spark plugs simultaneously. One plug fires on the compression stroke, igniting the fuel-air mixture. The coils are mounted together in a coil pack.
A variation of the direct fire ignition is the coil-on-plug system, which has individual coils for each spark plug. The coils are mounted near or directly on top of the spark plug. This eliminates the need for spark plug wires. The result is greater reliability because leaks from aging spark plug wires are nonexistent. The Cadillac Seville and Eldorado models, with the Northstar engine, employ this variation of direct fire ignition.
Engine Control Module
The engine control module (ECM) energizes the appropriate coil. To accomplish this, the ECM receives signals from either a magnetic crankshaft sensor or camshaft position sensor, or both, to determine crankshaft position and engine speed.
The direct fire ignition system avoids the need to switch very high voltages, which is troublesome with distributors in a damp environment. The direct fire ignition allows finer levels of ignition controls and assists in increasing output, increasing fuel efficiency and reducing emissions.
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