CNG

This is an Open Loop mode. During engine warm up, the Powertrain Control Module (PCM) receives inputs from:
- Battery voltage
- Crankshaft position sensor
- Engine coolant temperature sensor
- Intake manifold air temperature sensor
- CNG fuel low-pressure sensor
- CNG fuel temperature sensor
- Manifold absolute pressure (MAP) sensor
- Throttle position sensor (TPS)
- Camshaft position sensor, in distributor
- Park/Neutral Switch (gear indicator signal auto. trans. only)
- Air conditioning select signal, if equipped
- Air conditioning request signal, if equipped
- Vehicle speed sensor

Based on these inputs, the following occurs:
- Voltage is applied to the fuel injectors with the PCM controlling injection sequence, rate and injector pulse width. This is done by turning the ground circuit to each individual injector on-and-off at the PCM.
- The PCM begins firing ignition based on crankshaft position sensor input.
- The PCM adjusts the engine idle speed through the idle air control motor
- The PCM operates the air conditioning (A/C) compressor clutch through the A/C clutch relay. This is done if A/C has been selected by vehicle operator and requested by A/C thermostat
- When the engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The system will leave warm-up mode and go into Closed Loop operation