Fuel Rail Tuning Adjustment (Bi-Fuel Only)
WARNING:
Certain steps in this procedure require the vehicle to be running, in gear and the engine accelerated. Be sure that the parking brake is fully set and the wheels are correctly chocked. Take all necessary precautions to avoid injury and property or equipment damage.
WARNING:
The alternative fuel (CNG or LPG) lines and components are pressurized. Use care when servicing the system and take all necessary precautions to avoid personal injury. Always follow all applicable procedures concerning fuel leak testing and fuel system inspection.
- Place the vehicle in an appropriate service bay, set the parking brake, and correctly place wheel chocks both in front of and behind the front wheels. Connect the exhaust to a vacuum exhaust system and provide adequate ventilation.
- Select the OFF position of the ignition switch, and the ALT position of the ALT fuel selection switch.
- Connect the vacuum/pressure tester to an appropriate source of intake manifold vacuum.
- Connect the New Generation STAR (NGS) Tester to the vehicle diagnostic Data Link Connector (DLC). Turn the ignition switch to the ON position. Select, monitor, and record Powertrain Control Module (PCM) data PIDs ECT, O2S11, and O2S21.
- Start and run the engine while monitoring the PCM PID ECT. Allow the engine to warm up until the PCM PID ECT indicates 190°F.
- Select, monitor, and record the Alternative Fuel Control Module (AFCM) PID MAP and vacuum. Place the transmission gear selector in Reverse while applying the brake pedal then slowly apply pressure to the accelerator pedal. Continue to accelerate until the AFCM PID MAP indicates 7.3-7.4 PSI and record the vacuum. This vacuum value point will be used in the remaining procedure steps as the "tuning point".
- Allow the accelerator to return to the idle position and place the transmission gear selector in the Park position.
- Locate the two adjustment screw holes on the top of the tuning tee assembly, remove any sealant and access the adjustment screws. See Fig 1.
- Position both tuning tee adjustment screws to their "neutral" state by turning them counterclockwise with a slotted screwdriver until the screw head tops are flush with the top of the tuning tee and then turning them clockwise two complete turns.
- With the engine at idle speed and the transmission gear in the park position, select the NGS GRAPH option. Record ten seconds of data from PCM PIDs O2S11 and O2S21 (1 and 2). Retrieve the recorded data and identify which of the OS2 signals displays the longest high state time (1). See Fig 2.
- Use an assistant in the driver seat to repeat step 6. Obtain and hold the "tuning point" vacuum value.
- Select the NGS GRAPH option and record 10 seconds of data from PCM PIDs O2S11 and O2S21. Allow the accelerator to return to the idle position and place the transmission gear selector in the Park position.
- Retrieve the recorded data and identify which of the OS2 signals displays the longest high state time as in step 10.
- Determine which of the tuning tee adjustment screws requires adjustment. This is the only screw to be adjusted throughout the entire tuning tee procedure and is determined by the following: The PCM PID O2S11 data reflects the upstream bank 1 O2S and is adjusted with the passenger side tuning tee adjustment screw (1). The PCM PID O2S21 data reflects the upstream bank 2 O2S and is adjusted with the driver side tuning tee adjustment screw (2). See Fig 1. To reduce the PCM PID O2S11 or O2S21 high state time the corresponding adjustment screw is turned clockwise and to increase the high state time the adjustment screw is turned counterclockwise.
- Turn the tuning tee adjustment screw identified in step 13 one complete turn clockwise and repeat steps 10 through 12.
- Retrieve and compare the current graphed PCM PIDs O2S11 and O2S21 data with the previous data. If the determined PCM O2S PID from the previous graphed data continues to have the longer high state time, repeat steps 15 and this step.
- If the determined PCM O2S PID from the previous graphed data now has a shorter high state time, turn the corresponding tuning tee adjustment screw counterclockwise 1/2 turn and repeat steps 10 through 12.
- Retrieve and compare the current recorded graphed PCM PIDs O2S11 and O2S21 data. If necessary, continue to turn the same adjustment screw by 1/4 and 1/8 turn increments clockwise or counterclockwise as described in step 14 repeating steps 10 through 12 with each adjustment until both O2S PIDs display equal high state time. See Fig 3.
- When the retrieved PCM PIDs O2S11 and O2S21 data display equal high state time, the alternate fuel system is correctly tuned and no further adjustment is required. Document the following information: VIN, date, lead technician, assistant, O2S bank number adjusted, required number of turns to adjustment screw (to nearest 1/8th turn).
- Turn the ignition switch to the OFF position and remove the vacuum gauge and restore the intake vacuum system.
- Paint mark the tuning tee adjustment screw positions and seal the access hole with a manufacturers sensor safe sealant. Cover and label the adjustment screw cavities indicating that the alternative fuel system tuning procedure has been performed. Update all necessary vehicle inspection labels and placards.
WARNING:
This step requires the vehicle to be running, in gear and the engine accelerated. Be sure that the parking brake is fully set and the wheels are correctly chocked. Take all necessary precautions to avoid injury and property or equipment damage.
WARNING:
Never remove the tuning tee adjustment screws while the low pressure fuel lines are pressurized. Use caution when setting the adjustment screws. If the adjustment screws become dislodged from the tuning tee serious personal injury may result.
WARNING:
This step requires two people while the vehicle is running, in gear, and the engine accelerated. Be sure that the parking brake is fully set and the wheels are correctly chocked. Take all necessary precautions to avoid injury and property or equipment damage.