Volvo Coupes, Sedan, Wagons Repair Manual 1990-1998

• Volvo 240 Series
• Volvo 740, 760, and 780 Series
• Volvo 850 Series
• Volvo 940 and 960 Series
• Volvo C70, S70, and S90 Series
• Volvo V70, V90 Series

The B6304 engine is the only engine equipped with a distributor less ignition system. Each cylinder is equipped with an individual ignition coil. The coil is located over the spark plug, just like the spark plug boot; this style is referred to as "coil over plug". Using separate coils for each plug guarantees a very high voltage (approximately 49kV) and rapid power build up. This results in effective initiation of the combustion process and improves cold start performance. The ignition coils are controlled by two power stages (ignition modules). One module is connected to cylinders 1,3 and 5 and the other to 2,4 and 6. The power stages each incorporate three separate drivers, one for each ignition coil. The power stages are controlled by the ECM, which receives inputs from various sensors and other components. The ECM computes ignition timing and activates the power stage controlling current to the ignition coils. During start-up, the ECM ensures a fixed timing and ignition voltage, but, after start-up, the ECM continually computes optimum ignition requirements based on engine speed, engine load, engine temperature, and combustion timing.