See Figures 1, 2, 3 and 4
There are 2 types of electronic ignition systems used on Isuzu trucks: one uses a conventional centrifugal advance type distributor. The second system uses a fully transistorized type distributor.
Conventional type distributors are made up of the distributor shaft, rotor shaft, rotor head, breaker assembly, reluctor, governor flyweight, pinion gear and vacuum control unit.
Transistorized distributors consist of dust bushing, rotor, pinion and a crank angle sensor built into the distributor housing. The crank angle sensor uses a photo-electric pick-up to measure piston position and engine speed.
The computer, or Electronic Control Module (ECM), monitors the information from the engine sensor network. The ECM uses this information to calculate the proper spark timing and tell the distributor when to make timing modifications.
Some engines are equipped with an Electronic Spark Control (ESC) system. At the heart of the ESC system is the knock sensor which is mounted to the engine block. The knock sensor is connected to the electronic spark control module which is located on the right fender panel in the engine compartment or on a bracket mounted to the block. In response to engine knock, the sensor transmits a signal to the electronic spark module (half function box''). The spark control module sends the signal to the ECM which in turn tells the distributor to retard the spark timing up to 20° to reduce spark knock in the engine.