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Fuel Tank Venting (CNG)

WARNING: This page is about a different car, the 2002 Pontiac Sunfire and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
WARNING: Venting of CNG to the atmosphere may be prohibited in some areas. Before venting the CNG fuel tank, contact the local gas company to ensure that all local, state and federal regulations are observed.
WARNING: When venting a CNG fuel tank, take the following precautions to prevent fire and personal injury:
  • Use proper grounding procedure to an earth ground to prevent a build-up of static electricity, which can lead to an electrical discharge.
  • Use CNG Tank Vent Kit (J 42435) with a vent stack.
  • Vent CNG fuel tank in a well ventilated work area.
  • Keep sparks, flames, and smoking material away from vent area.
  • Wear appropriate hearing protection during venting procedure. A sudden pressure loss from an uncontrolled gas leak can cause hearing damage.
CAUTION: Venting cannot be stopped once the High Pressure Lock-Off (HPL) has been opened using manual vent tool. The manual vent tool can damage main seat of HPL if used improperly. Use this tool only when HPL is not in operation.
CAUTION: Replace all "O" rings that are disconnected or loosened.
NOTE: Only vent CNG fuel tank if HPL is replaced, or tank is to be cleaned, replaced or shipped.
  1. Remove spare tire cover. Remove jack and tool kit. Remove spare tire. Remove 4 tank cover bolts. Remove tank cover.
  2. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE (CNG) .
  3. Turn ignition off. Disconnect negative battery cable.
  4. Remove the fuel line vent boot cover nuts. See Figure. Remove fuel line vent boot cover. Disconnect all electrical connectors in order to remove the vent boot cover from the tank area.
  5. Disconnect the CNG fill line from the HPL. Remove the Fuel Pressure Sensor (FPS). Disconnect the CNG fuel outlet line from the HPL. Install a cap supplied with tank vent kit onto the fuel outlet line fitting and FPS fitting at the HPL. Tighten the caps to 27 ft. lbs. (37 N.m). Install a cap on FPS port fitting. Tighten cap to 35 ft. lbs. (48 N.m).
  6. Remove the CNG fill line and fuel line vent fittings from the HPL. Install a double-male fitting supplied with tank vent kit into CNG fill line and fuel line vent ports at the HPL. Tighten fittings to 35 ft. lbs. (48 N.m).
    7. NOTE: Refer to tank vent kit container for instructions on how to properly construct a vent stack.
  7. Connect the female end of the vent hose supplied with tank vent kit into CNG fill line port at the HPL. Connect the male end of the vent hose to a vent stack.
  8. Connect ground strap (attached to vent hose) to the FPS port fitting at the HPL and to vent stack earth ground.
    9. CAUTION: If you were required to close the manual lock-down screw during the FUEL PRESSURE RELIEF PROCEDURE, the tank may begin to vent when the lock-down screw is opened.
  9. Ensure that the manual lock-down screw of the manual shut-off fitting is open by rotating the Allen screw counter-clockwise until fully seated. See Figure. If the tank begins venting when the manual lock-down screw is opened do not proceed to the next step until the tank stops venting.
  10. Remove the manual shut-off fitting from the HPL. Rotate the Allen screw with the manual vent tool counter-clockwise in order to fully retract the plunger. Install the manual shut-off fitting into the HPL port with the plunger fully retracted. Tighten the manual shut-off fitting to 108 ft. lbs. (12 N.m).
  11. Slowly rotate the Allen screw with the manual vent tool clockwise until the plunger is fully extended. Open the tank vent kit in-line valve. The tank should always contain some pressure and begin to vent.
  12. Allow CNG fuel tank to vent until tank vent kit pressure gauge reads 0 psi (0 kPa). If tank stops venting and pressure is indicated on gauge, check for frozen vent line fitting. If frozen, fitting will eventually thaw and fuel will continue to vent. Do not leave tank unsupervised while venting.
  13. After tank is completely vented, disconnect vent hose from HPL. Remove manual vent tool and all fittings. Remove fuel inlet fitting from HPL and discard "O" rings. Remove fuel outlet fitting from HPL and discard "O" rings. Remove HPR relief device and discard "O" rings. If the tank is to be reused replace the HPL. See HIGH PRESSURE LOCK-OFF .
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