Ignition System - Electronic: Operation

Inputs from engine speed, engine load, detonation, throttle position and battery voltage are supplied to the microprocessor within the ignition module to determine spark advance. Only the engine load and engine speed input signal values are used to determine the timing signal entered in the memory of the microprocessor. The microprocessor, after analyzing the parameters of engine operation, will adjust timing accordingly.

The ECU output signals provide control for the amplifier module, whose final transistor will make or break the primary coil circuit. The output signals also control the full load enrichening circuit of the injection ECU and the LED knock indicator.

The Volvo B280F engine utilizes 2 knock sensors, one for each cylinder bank. They are located below the intake manifold in the center of the block.

The knock sensors consist of piezo-electric transducers which produce a current within the frequency range which occurs when a cylinder knocks. The ECU will retard ignition timing by 3 degrees for the individual cylinder that developed knocking. When knocking stops, the ECU will hold the retarded ignition timing for a number of revolutions, depending on engine speed.