High Pressure Regulator (HPR)

The HPL is a normally closed, solenoid valve. The HPL solenoid and a Low Pressure Lock-off (LPL) solenoid in the fuel line prevent fuel flow. The AF ECU commands ONLY the HPL open for 1 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 the Fuel Pressure Sensor (FPS) to monitor the amount of fuel pressure in the tank. The AF ECU commands BOTH the HPL and the LPL open when engine RPM indicates the engine is cranking or running on CNG.