Ignition Control Module: Description and Operation

The Ignition Timing Power Transistor is controlled by the MPI Control Unit. The Control Unit monitors the returning input signals (during normal driving conditions) computes the correct spark advance or retard, and then actuates the transistor accordingly. While the engine is cranking, the ignition timing is fixed at 5°BTDC
The power transistor is located on the intake manifold and works in a similar manner as the points on a conventional ignition system. When activated, the transistor interrupts the ignition coil primary circuit ground inducing a voltage into the secondary circuit.