Engine Timing

The PCM controls both duration and timing of injection event with Fuel Delivery Control Signal (FDCS). Signal duration, or fuel pulse width, is shown as FUEL_PW PID on scan tool. PCM controls fuel plunger injection pressure and fuel volume by varying injection oil pressure with Injection Pressure Regulator (IPR). The command to IPR is a 12-volt, Pulse Width Modulated (PWM) signal (controlled on ground side). Injection oil pressure command is shown as NGS PID IPR which is the percentage ON of pulse width modulated signal. Injection oil pressure is shown as NGS PID ICP. PCM receives engine rotational position information from Camshaft Position (CMP) sensor. CMP is a Hall effect device. It outputs 12 volts to PCM whenever it detects iron of a spoked target wheel in front of it, and it outputs zero volt whenever it detects space between spokes. The target wheel spokes and spaces are each 15 crank degrees, except for narrow spoke which indicates cylinder No. 1 and a wide spoke which indicates cylinder No. 4 (fires 5th). Scan tool RPM PID is generated by PCM from CMP signal.