COMMANDS FROM THE ECM

The primary job of the ECM is to control the amounts and timing of the fuel that’s injected into the engine cylinders. It‘s achieves this by controlling components inside the fuel pump. The timing of injection is controlled using a solenoid and spring loaded plunger. The plunger moves under normal pump pressure. A single from the ECM energises the solenoid, moving the plunger against the spring pressure reducing the fuel pressure and retarding the increases and the injection timing. When the solenoid has been de energized fuel pressure increases and the injection timing is advanced. The ECM sets two fuel quantity levels and controls the amount though the quantity servo assemblies inside the fuel injection pump. The servo comprises a magnet rotating around a vertical shaft.

The shaft operates the quantity control spool at its lower end and a potentiometer at its upper end. The ECM energises a coil that moves the magnet, causing the shaft to rotate, thus adjusting the quantity spool and the potentiometer. When the ECM de energies the coil an integral return spring brings both the vertical shaft and the control spool back to zero fuel position. Current fuel quantity is the actual fuel demand calculated by the ECM according to engine load. The quantity call for varies between zero and 100 milligrams of fuel per piston firing stroke.

Fuel quantity limited is calculated by the ECM and used to govern the actuator to prevent over fuelling. Under sudden engine load this limit can be breached briefly. Before setting back to below the limit value. The heater plugs are operated via a timer control relay, with the duration dictated by the ECM according to the engine temperature at start up.