See Figures 1 and 2
Beginning with the redesigned 1988 Civic, Honda began using a computer-controlled Programmed Ignition (PGM-IG). Only evolutionary changes to component design were made for 1992 and later models. The PGM-IG consists of a distributor driven directly from the front camshaft, an amplifier mounted on the side of the distributor and a high energy coil.
The distributor contains a reluctor mounted on a rotor shaft and a magnet mounted on a base plate. Within the distributor are also the sensors for top dead center (TDC), crank position sensor (CKP), and cylinder position sensor (CYP) on 1992 and later models.
The PGM-IG employed on these vehicles controls ignition timing by using a microcomputer known as either Electronic Control Unit (ECU) 1988-92, or Electronic Control Module (ECM) 1993-on. By whatever name, this engine management device has stored within its memory the optimum basic ignition timing for operating conditions based upon engine speed and vacuum pressure in the intake manifold. Information about these ever-changing variables is transmitted by signals from the TDC/CKP/CYP (as applicable) sensors, as well as a coolant temperature sensor and Manifold Absolute Pressure (MAP) sensor. These sensors and the microcomputer also serve the interdependent Programmed Fuel Injection system (PGM-FI) described in Fuel System . The PGM-IG system is not dependent upon a conventional governor or vacuum diaphragm and is capable of controlling timing with complicated characteristics which cannot be provided by these non-computerized systems.
The amplifier connected directly to the pick-up coil contains three resistors, three diodes and two transistors. The transistors act as switches which are activated at a precise voltage.
When the ignition is switched ON , the switching of the transistors in the amplifier ensures that no current can flow in the ignition coil primary windings. When the engine is cranked, the reluctor moves through the magnetic field created by the stator and, when the reluctor teeth are aligned with the stator projections, a small AC voltage is created. The amplifier boosts this voltage signal and uses it to switch the transistors so that a ground path is provided to the primary circuit.
As the reluctor teeth move out of alignment with the stator projections, an abrupt change occurs in the AC voltage. The transistors are switched again and the primary circuit ground path is broken. This induces a high voltage in the ignition coil secondary winding.
A time control circuit in the amplifier controls the charging time for the ignition coil according to engine speed, this reduces consumption at low engine speeds and prevents secondary voltage drop at high engine speeds.