Direct Ignition Systems are the ignition coil mounted on the spark plugs. The Direct Ignition Systems come in two forms: a) Independent Power – a coil for each cylinder. You do not use spark plug wires. b) On Concurrent – a coil for every two cylinders. In this arrangement a coil is mounted directly on a candle and a high voltage cable connects the cylinder spark plug "brother." In this way the spark is generated in both cylinders at a time. Simultaneous Operation System Ignition Distributor Ignition Systems Distributor and Direct Ignition Systems that use a coil for every two cylinders using the method known as simultaneous switching, as we saw. With simultaneous lighting systems, two-cylinder "pair" in accordance with the position of the piston. This has the effect of simplifying the start-up time and reduce the voltage level required for the secondary circuit.
For example, consider in detail what happens in particular in the cylinders 1 and 4 in a V-6 engine. We know that in the vast majority of all V-6 engine almost every brand, every year the "firing order" is always the same: 1-2-3-4-5-6, except for some rare exceptions. We also know that these engines the cylinders 1 and 4 are "twinned", ie that both pistons occupy the same position (the two are in the PMS and PMI at the same time), move in unison, however, are working in different races. When cylinder 1 is in the compression stroke in the first revolution, the cylinder 4 is in the exhaust stroke, vice versa in the next revolution and so on while the engine is turning.