Fuel Tank Venting Procedure

Venting cannot be stopped once the High Pressure Lock-Off (HPL) solenoid has been opened using the manual vent tool. Venting the CNG fuel tank will damage the HPL solenoid. Venting is only necessary for high pressure lock-off replacement, internal tank cleaning, tank replacement or tank shipping.

1. Remove the CNG fuel tank cover. See FUEL TANK COVER  . Remove the truck body or side panel as required on RPO ZW9 equipped vehicles in order to gain access to the right side of the CNG fuel tank. On all models, relieve the fuel system pressure. See FUEL PRESSURE RELIEF PROCEDURE  . Disconnect the negative battery cable(s). Disconnect the fuel outlet line from the High Pressure Lock-Off (HPL) solenoid. Disconnect the tee fitting from the HPL inlet fitting. Remove the HPL inlet fitting.
2. Remove the Fuel Tank Pressure (FTP) sensor. Install fittings supplied from CNG Tank Venting Kit into all of the HPL solenoid fuel ports as necessary. It is not necessary to install a fitting and cap in the Pressure Relief Device (PRD) outlet port. Tighten the fittings to specification. See TORQUE SPECIFICATIONS  . Install caps supplied from CNG Tank Venting Kit onto the FTP port fitting and the fuel outlet fitting as necessary. Tighten the caps to specification.
WARNING: When venting the Compressed Natural Gas (CNG) fuel tank take the following precautions in order to prevent fire and personal injury: use the proper grounding procedure to an earth ground in order to prevent a build-up of static electricity which can lead to an electrical discharge, use the CNG Tank Vent Kit with a vent stack, vent the CNG fuel tank in a well ventilated work area, keep sparks, flames, and smoking material away from the area and wear the appropriate hearing protection during the venting procedure. A sudden pressure loss from an uncontrolled gas leak can cause hearing damage.
3. Connect the female end of the vent hose to the fuel line fitting. Connect the male end of the vent hose to a vent stack. Refer to CNG Tank Venting Kit container for instructions on how to properly construct a vent stack. Connect the ground strap to the FTP sensor port fitting and to the vent stack earth ground.
WARNING: 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.
4. Ensure that the manual lock-down screw of the manual shut-off fitting is open by rotating the Allen screw counterclockwise until fully seated. If the tank begins venting when the manual lock-down screw is opened do not proceed until the tank stops venting.
5. Remove the manual shut-off fitting from the HPL solenoid. Obtain the manual vent tool supplied from the CNG Tank Venting Kit. Rotate the screw on the manual vent tool counter-clockwise in order to fully retract the plunger. Install the manual vent tool into the HPL solenoid port with the plunger fully retracted. Tighten the manual vent tool to specification. Slowly turn the manual vent tool screw clockwise until the plunger is fully extended.
6. Open the tank vent kit in-line valve. The tank should always contain some pressure and begin to vent. Do not leave the tank unattended during venting. Allow the CNG fuel tank to vent until the pressure gauge reads 0 psi (0 kPa). If the tank stops venting and pressure is indicated on the tank vent kit gauge, inspect the vent line for a frozen fitting. The fitting will eventually thaw and fuel will again continue to vent. Inspect for freezing near the HPL. A frozen HPL may stop fuel flow temporarily and show 0 psi (0 kPa) on the pressure gauge.
7. When the tank is completely vented, remove the vent line from the fuel fitting. Remove all the fittings and caps as necessary. Remove the manual vent tool. If the tank is to be re-used, replace the high pressure lock-off. See HIGH PRESSURE LOCK-OFF SOLENOID  under SOLENOIDS.