An actuation timing apparatus is disclosed for providing triggering and steering control signals to an electronic control unit regulating a plurality of solenoid fuel injectors of a sequential injection system. The apparatus includes a rotatable member which is rotated in synchronism with the engine at the speed of its camshaft. The rotatable member has a plurality of spaced sensible elements geometrically disposed thereon and divided into groups identifying individual cylinders. Each group has at least one sensible element which defines a reference element having a recognizable characteristic distinguishing it from the other sensible elements in the group. A single sensor senses the spaced sensible elements of each group as they rotate past a fixed sensing location and generates corresponding electrical pulses to a pulse processing circuit. The pulse processing circuit decodes each group of pulses to provide the identity of the injector to be next actuated. The pulse processing circuit recognizes the reference element and an enabling element of each group to generate an enabling signal to the electronic control unit (ECU) indicating that the decoding process for the group has been accomplished. The decoded information is sampled upon receipt of the enabling signal and causes the electronic control unit to steer the next injection pulse to the identified injector.