Ignition System: Description and Operation

NON-TURBO
The ignition system used on naturally aspirated Probe models is a fully transistorized high energy system, similar to the Duraspark ignition. Vacuum and centrifugal advance units are used in the distributor. Ignition timing is advanced by vacuum at low speeds and by a centrifugal mechanism at high speeds. At altitudes greater than 6,500 ft., the Electronic Control Assembly (ECA) modifies engine timing to maintain proper exhaust emissions and engine performance. Current flows to the ignition coil's primary winding and is grounded through the ECA. When an ignition signal is generated, the magnetic pickup in the distributor aligns with the distributor sensor coil inducing a current which closes an electronic switch and applies a voltage to both sides of the primary winding. Voltage to both sides of the primary winding removes the ground to the winding and interrupts its current flow. Interruption of the current flow induces a high voltage in the coils secondary winding sending pulses to ground through the distributor which is then used to fire the spark plugs.

TURBO
The ignition system used on turbocharged Probe models is completely electronic and is controlled by the ECA. Electronic sensors and switches send triggering signals to the ECA, which in turn send spark timing signals through the ignition module to the distributor. Cylinder TDC sensors let the distributor indicate to the ECA, when the crankshaft is at top dead center. The trigger signal, electronic sensors and switches used in this system are as follows: The vane airflow meter, clutch engage switch, idle switch, neutral gear switch, EGR valve position sensor, engine coolant temperature sensor and switch, knock sensor and the throttle position sensor.
Current flows through the ignition coil's primary winding and is grounded through the ECA (ground G103). When the ECA sends a ignition signal to the ignition module, an electronic switch in the module opens and closes current through the primary windings. Interruption of the current flow induces a high voltage in the coils secondary winding sending pulses to ground through the distributor which is then used to fire the spark plugs

The non-electronic components, used in this system are as follows: the battery, starter interlock switch, distributor, ignition module, high tension wires and spark plugs.