System Description

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Savana, 2003 Chevrolet Silverado, and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

The PCM controls the fuel system while the vehicle is operating on CNG. The PCM receives signals from various engine sensors and determines the correct amount of fuel required by the engine. Fuel is stored in cylindrical fuel tanks. A full tank can contain fuel at 3600 psi (24,820 kPa). A High Pressure Lock-Off (HPL) solenoid in each tank and a Low Pressure Lock-Off (LPL) solenoid in the fuel line prevent fuel flow. The PCM commands only the HPL's open for one second at every ignition ON for a CNG prime pulse. The CNG prime pulse is performed in order to charge the fuel line and also allows Fuel Tank Pressure (FTP) sensor to monitor the amount of fuel pressure in the tanks. The PCM commands BOTH the HPL's and the LPL open when engine RPM indicates the engine is cranking or running on CNG.

This fuel delivery system utilizes a High Pressure Regulator (HPR) in order to lower the fuel pressure from tank pressure down to an injector delivery pressure. When the PCM commands the HPL's open, fuel begins to flow through the HPR. The HPR reduces pressure to between 130-200 psi (896-1379 kPa). The fuel exiting the HPR flows through the intermediate fuel line to the fuel rail mounted LPL solenoid. Fuel flows out of the LPL and through the fuel rails to the injectors.