Ignition System - 1.4L: Operation
Engine speed and crankshaft (piston) position are determined by the non-adjustable magnetic position sensor rather than the distributor. This sensor indicates position of top dead center and bottom dead center, as well as engine speed.
The vacuum sensor, mounted permanently on the computer housing, appears identical to vacuum diaphragms found on conventional ignition systems. However, the internal components differ greatly. Attempts to remove the vacuum sensor will break a small diameter wire leading into the computer, rendering it useless.
As the engine operates and the crankshaft flywheel turns, information is received by the computer indicating engine speed and crankshaft position. The vacuum sensor informs the computer of engine load conditions. See Fig 1.
The computer then interprets the information received, and sets the ignition advance ratio. The computer then opens and closes the primary circuit of the ignition coil, causing a build-up and collapse of the coil's magnetic field.
This in turn, causes a voltage surge in the secondary circuit of the coil. The distributor then furnishes spark to the appropriate spark plug in the correct firing order.