The Alternative Fuels SUPPLY system contains the following components:

Refer to Fuel Metering System Description for additional information regarding other alternative fuels components.

The CNG Fuel Tank is constructed of steel and is wrapped in carbon fiber set in epoxy. The high pressure lock-off solenoid is contained within the fuel tank and is used to prevent fuel flow during non-cranking or running engine conditions. Storage capacity of the tank varies with vehicle model. Refer to the owners manual supplement for storage capacity. Fuel tanks mounted in pick-up truck models also have a protective steel cover. The cover is designed to protect the tank from damage due to shifting cargo and ultra-violet (UV) radiation.

Regulations require that the fuel tank and brackets be inspected every three years or 36,000 miles (60,000 km), which-ever comes first. Fuel tank inspection results should be recorded in the CNG Fuel Tank Inspection Record area of the owners manual supplement (if applicable). The service life of the CNG fuel tank is 15 years from the date of manufacture. All CNG fuel tanks regardless of inspection results must be replaced after  15 years. Refer to Fuel Tank Inspection procedures.

The fill valve receives fuel from the fill nozzle at the CNG dispensing station. The fill valve seals to the dispensing nozzle with an O-ring. Before re-fueling this O-ring must be inspected and replaced if missing or damaged. The fill valve contains an internal filter element designed to trap contaminants. This filter must be periodically inspected and cleaned. Refer to Fill Valve Filter Replacement for filter inspection and cleaning procedures. The fill valve mounting location varies with vehicle model. Refer to the owners manual supplement for fill valve location and fuel tank filling procedures.

The fill line is constructed of 3/8 in. flexible, steel-braided hose protected by a plastic cover. The fill line connects the fill valve to the fuel tank and is sealed to the fuel tank with an O-ring.

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.

The FPS is a pressure transducer. The AF ECU supplies about 5 volts on the FPS reference circuit. The AF ECU also supplies a signal and ground circuit to the FPS. Located at the end of the fuel tank, threaded into the HPL, the FPS supplies a voltage signal to the AF ECU. With a full fuel tank (high pressure) a high voltage signal will be monitored by the AF ECU.

Since CNG is a gaseous fuel it's volume will vary with temperature and pressure. This will vary the amount of fuel vs. the signal voltage the FPS supplies to the AF ECU. In order to compensate for the different voltage factors, a tank mounted (internal) fuel temperature sensor (FTS) is also monitored by the AF ECU. The AF ECU performs a calculation on the FPS voltage vs. the in-tank temperature. The AF ECU will then control the fuel gauge to display the correct fuel level.

The FTS is a thermistor mounted inside the HPL and is not serviceable separately from the HPL.

The FTS thermistor has high resistance when cold and low resistance when hot. The AF ECU supplies about 5 volts to the FTS signal circuit. When FTS resistance is high (cold sensor) the FTS signal voltage is high. As the FTS warms and resistance drops, less signal voltage is monitored by the AF ECU.

Since CNG is a gaseous fuel it's volume will vary with temperature and pressure. This will vary the amount of fuel vs. the signal voltage the FPS supplies to the AF ECU. In order to compensate for the different voltage factors, the tank mounted (internal) fuel temperature sensor (FTS) is monitored by the AF ECU. The AF ECU performs a calculation on the FPS voltage vs. the in-tank temperature. The AF ECU will then control the fuel gauge to display the correct fuel level.

The fuel system uses three different fuel line types (not including the fill line). The type used is dependent upon the pressure it is designed to handle.

High Pressure Line

The high pressure line is stainless steel tubing with matching high pressure O-ring face seal (ORFS) fittings. The individual tubes are pre-formed with fittings installed. All O-ring face seal fittings use nitrile rubber O-rings and might be identified with a yellow or white band. These O-rings must be replaced with the correct replacement part whenever a line is opened.

When installing NPT (pipe thread) fittings DO NOT use Teflon® tape. Tape fragments could lodge in a regulator and allow fuel pressure to exceed specified levels. The use of pipe sealant with Teflon® is required.

Intermediate Pressure Fuel Hose

The intermediate pressure fuel hose assembly is a unique two-piece stainless steel braided hose and is designed to isolate AF components from vibration.

Low Pressure Hose

Low pressure gas is supplied to the gas mass sensor / mixture control valve (GMS / MCV) and also to the gas distribution adaptor (GDA) with Gann® VH-100 vapor hose. This hose is a patented non-permeable hose.

All hose, lines and fittings must be replaced ONLY with the correct replacement GMSPO part number.