1. PCM Calculation: The PCM calculates the required fuel injection duration based on various sensor inputs (like throttle position, engine speed, coolant temperature, oxygen sensor, etc.).
2. PCM Output: The PCM then sends a *ground signal* to the injectors. It's crucial to understand it's a *negative* pulse; the injectors are normally energized by a constant +12V supply. The PCM briefly grounds the injector's control circuit, completing the circuit and allowing current to flow, opening the injector.
3. Injector Driver (Sometimes Integrated): While some systems might have a separate injector driver module, in many 1988 Jeeps the driver circuitry is integrated within the PCM itself. This circuitry handles the high current demands of the injectors, protecting the PCM from damage. The PCM's output signal is used to switch the higher current needed to open the injector.
4. Injector Wiring Harness: The signal travels from the PCM through a dedicated wiring harness to the individual injectors. Each injector has its own wire.
In short, the PCM's signal isn't directly a high-current pulse sent to the injector. It's a low-current signal that *controls* the higher-current path to the injector, allowing it to open and inject fuel. The pulse width determines the amount of fuel injected. This system is called ground-switching injection.
