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Home >> GMC >> 2013 >> Sierra 1500 Denali, AWD >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Engine Controls/Fuel - 4.8L, 5.3L, 6.0L, 6.2L - Repair Instructions >> Repair Instructions >> Compressed Natural Gas Tank Venting >> Venting Procedure
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Venting Procedure

    WARNING:

    Natural gas is highly flammable. In order to reduce the risk of fire and personal injury, keep sparks, flames, and smoking materials away from the vehicle while you perform the Compressed Natural Gas (CNG) fuel system service.

    WARNING:

    The Compressed Natural Gas (CNG) system operates at pressures up to 24820 kpa (3600 psi). Relieve the CNG fuel system pressure before servicing CNG fuel system components in order to reduce the risk of fire and personal injury.

  1. If the fuel system is near empty, you may run the vehicle until the tank is empty. The Engine will stall or switch over to gasoline.
  2. If fuel system is not empty then relieve the low pressure side of the manual shutoff valve fuel pressure. Refer to Compressed Natural Gas Fuel Pressure Relief (High Pressure Side of the Manual Shutoff Valve) , Compressed Natural Gas Fuel Pressure Relief (Low Pressure Side of the Manual Shutoff Valve) .
  3. Select a suitable SAE 8 O-ring fitting or CH-51205  Fuel Pressure Release Schrader Valve and install it in the vacated boss in the fuel rail. This fitting will be used to connect to a vent stack or other safe venting conduit. If using CH-51205  Fuel Pressure Release Schrader Valve connect the CH-48027  Digital Pressure Gauge to connect to the vent stack.
    1. If using CH-51205  Fuel Pressure Release Schrader Valve connect the CH-48027  Digital Pressure Gauge to connect to the vent stack.
    2. If using a SAE 8 O-ring fitting, route a pressure relief hose into an approved vent stack attached to an area outside the building.
    4. NOTE:

    The pigtail harnesses do not have polarity.

  4. Keeping the manual valve closed, open the regulator solenoid by applying 12 volts to the pigtail harness with a fused jumper wire and open the tank solenoid with CH-51210  Vent Valve Override Tool ,or by applying 12 volts to the pigtail harness with an additional jumper wire.
  5. The CH-51210  Vent Valve Override Tool should only be used if the Fuel Tank solenoid valve is inoperable (Stuck closed).
  6. The CH-51210  Vent Valve Override Tool will destroy the internal seals of the valve rendering the valve inoperable. Refer to Compressed Natural Gas Venting Tool .
  7. Slowly open the manual shutoff valve and allow the tank and fuel system to vent through the fuel rail connection to the vent stack until the tank is completely depressurized.
  8. The CNG fuel tank is completely vented when all of the following conditions have been met:
    • Venting gas flow is no longer audible from the vent stack.
    • If ambient temperature is lower than 7°C (45°F), warm the fuel tank and vent assembly by placing in a warm environment or spraying with warm water.
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