Ignition Systems: DISTRIBUTORLESS: Legacy

Distributorless ignition system is controlled by ECU. System consists of 2 ignition coils and a power transistor assembly. Power transistor assembly consists of 2 transistors, which control primary current path to ground for each ignition coil. One transistor controls primary path to ground for ignition coil, which fires cylinders No. 1 and 2. Other transistor controls primary path to ground for ignition coil, which fires cylinders No. 3 and 4.

Although each coil fires 2 plugs simultaneously, ignition takes place in only one cylinder, since other cylinder is on its exhaust stroke when plug fires. Based on input from crankshaft and camshaft angle sensors, ECU signals base of appropriate power transistor. This allows primary current flow to ground. Ignition coils receive primary power supply when ignition coil relay is energized.