Engine Control System - 6.0L - Alternative Fuel (Introductions): Other GMC Savana G2500

Compressed Natural Gas (CNG) Temperature vs Percent Full

Compressed Natural Gas (CNG) Temperature vs Percent Full

Fuel Tank Pressure (FTP) Sensor Output Voltage vs Pressure

Fuel Tank Pressure (FTP) Sensor Output Voltage vs Pressure

Fuel Rail Pressure (FRP) Sensor Output Voltage vs Pressure

Fuel Rail Pressure (FRP) Sensor Output Voltage vs Pressure

Fuel Tank Temperature (FTT) Sensor Output Voltage vs Temperature Resistance

Fuel Tank Temperature (FTT) Sensor Output Voltage vs Temperature Resistance

Fuel Temperature Sensor (FTS) Output Voltage vs Temperature Resistance

Fuel Temperature Sensor (FTS) Output Voltage vs Temperature Resistance

Fuel Rail Temperature (FRT) Sensor Output Voltage vs Temperature Resistance

Fuel Rail Temperature (FRT) Sensor Output Voltage vs Temperature Resistance

Engine Controls Components

Engine Controls Components

Scheme 22

Scheme 23

Fuel Pressure Relief Procedure

Tools Required

J 42435 CNG Tank Venting Kit. See Special Tools and Equipment .

1. With a scan tool communicate with the PCM. If communication cannot be established and the «Diagnostic System Check - Alternative Fuels (Engine Controls)»(ref-185855-S02490023462005082900000) has already been performed proceed to Step 9.
2. Store the DTC Information with a scan tool.
3. Clear the DTC Information with a scan tool.
4. Turn OFF the ignition.
5. Start and idle the engine.
6. Ensure that the engine is operating on CNG by observing the following: The fuel indicator lamp (FIL) is OFF (KL6) The AFO Enable scan tool display indicates the engine is operating on alternative fuel.
7. With a scan tool, select the high pressure lock-off (HPL) solenoid special function.
8. While the engine is operating on CNG command the HPL solenoid OFF and observe the fuel tank pressure sensor data parameter. The fuel tank pressure should slowly decrease. If the fuel pressure fails to decrease proceed to Step 9. When the engine stalls or a switch-over to gasoline is observed, perform the following: Turn OFF the ignition. Remove the Alt. Fuels 20-amp fuse in order to disable the CNG fuel system. A small amount of CNG will remain in the fuel lines and components. Slowly open the fittings in order to release any remaining pressure when disconnecting a fuel line. Fuel Pressure Relief for the CNG system is now complete. Proceed to Step 16.
9. Close the manual lock-down screw located on the end of each high pressure lock-off (HPL) solenoid. The manual shut-off fitting is closed by rotating the allen screw clockwise until fully seated.
10. Turn OFF the ignition.
11. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical in the G/H Van Service Manual.
12. Slowly loosen the fuel line fitting (4) at the tee (1) several turns.
13. Fuel Pressure Relief for the CNG system is complete when the fuel line can be pulled away from the O-ring face seal and fuel does not vent.
14. Replace the O-ring face seals at all fittings that were disconnected or loosened.
15. After all necessary repairs are complete perform the following: Tighten any loosened fittings to the correct torque. Refer to «Fastener Tightening Specifications»(ref-185854-S04335593472005082900000) . IMPORTANT: Leave the manual lock-down screws closed on any vehicle that will require CNG fuel tank venting. Open the manual lock-down screws located on the HPL manual shut-off fittings by rotating the allen screw counter-clockwise until fully seated on any vehicle that does not require venting of the CNG fuel tanks.
16. If the service necessary for the vehicle requires the CNG fuel tanks to be relieved of all internal pressure, refer to «Fuel Tank Venting Procedure»(ref-185854-S17889565712005082900000) .

Level 1 Chips

1. Level 1 chips are chips or abrasions in the coating that do not penetrate the top coat.
2. Level 1 chips do not expose the gray zinc-rich primer.
3. Level 1 chips do not require resurfacing.

Level 2 Chips

1. Level 2 chips are chips or abrasions that penetrate the top coat.
2. Recoat Level 2 chips or abrasions in order to prevent corrosion
3. The following two repair methods are recommended depending on whether the zinc-rich primer is still intact: Method 1: Recoat the chip using any commercial room temperature cure two-component epoxy resin, Loctite® Part No. 14600 or equivalent, if the chip has not penetrated the zinc-rich primer. Method 2: The following procedure is recommended if the chip has penetrated the zinc-rich primer and exposed the bare metal: Sand the damaged area in order to remove any rust and to rough-up the surrounding coating. Clean the damaged area with a commercial prepaint cleaning solvent-Dupont® Prep Sol or equivalent. Apply a zinc-rich cold galvanizing primer-LPS® Part No. 00516 or equivalent. Coat the area after the primer has cured using a room temperature cure two-component epoxy resin-Loctite® Part No. 14600 or equivalent.

Dents

Dents

Gouges

Gouges

Removing From Service

1. The CNG fuel tank has a fifteen year service life from the date of manufacture.
2. The CNG tank manufacture date appears on a label on the tank.
3. The tank expiration date is on the CNG Fuel Only label and the Bi-fuel Information label.
4. Any tank in service for fifteen years or more must be removed from service using the following procedure: Remove the tank. Refer to «Fuel Tank Replacement - Front (KL8)»(ref-185854-S18211563042005082900000) or «Fuel Tank Replacement - Rear (Passenger/Cargo)»(ref-185854-S24799367272005082900000) or «Fuel Tank Replacement - Rear (Cutaway)»(ref-185854-S08299222712005082900000) . Vent the tank. Refer to «Fuel Tank Venting Procedure»(ref-185854-S17889565712005082900000) . Disconnect the vent hose. Allow the tank to stand for 24 hours with either the tank valve energized or the manual valve opening tool installed. Place the tank outside in a well ventilated area. Drill a 0.64 cm (1/4 in) hole after the last digit of the tank identification number stamped into the valve end of the tank. Dispose of the tank in a safe and approved manner.

Fuel Tank Venting Procedure

Tools Required

J 42435 CNG Tank Vent Kit. See Special Tools and Equipment .

1. Relieve the fuel system pressure. Refer to «Fuel Pressure Relief Procedure»(ref-185854-S02905361662005082900000) .
2. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical in the G/H Van Service Manual.
3. Remove the fuel tank cover. Refer to «Fuel Tank Cover Replacement»(ref-185854-S01404073892005082900000) .
4. In order to vent the rear tanks on cargo/passenger vans the tanks must be removed from the vehicle. Refer to «Fuel Tank Replacement - Rear (Passenger/Cargo)»(ref-185854-S24799367272005082900000) or «Fuel Tank Replacement - Rear (Cutaway)»(ref-185854-S08299222712005082900000) if applicable.
5. Disconnect the fuel outlet line (4) from the tank.
6. Install a cap (3) supplied from the J 42435 on to the fuel line fitting of the fuel outlet port (4). See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) . Tighten: Tighten the cap to 37 N.m (27 lb ft).
7. Leave the fuel tank pressure (FTP) sensor installed if equipped.
8. Disconnect the fuel inlet line from the tank.
9. Connect the female end of the vent hose to the fuel line fitting.
10. Connect the male end of the vent hose (1) to a vent stack. Refer to the J 42435 container for instructions on how to properly construct a vent stack. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
11. Connect the ground strap to one of the fittings and to the vent stack earth ground (2).
12. Ensure that the manual lock-down screw of the manual shut-off fitting is open by rotating the allen screw counterclockwise until fully seated.
13. 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.
14. Remove the manual shut-off fitting from the HPL.
15. Obtain the manual vent tool supplied from the J 42435 . See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
16. Rotate the screw on the manual vent tool counter-clockwise in order to fully retract the plunger.
17. Install the manual vent tool into the HPL port with the plunger fully retracted. Tighten: Tighten the manual vent tool to 12 N.m (108 lb in).
18. Slowly turn the manual vent tool screw clockwise until the plunger is fully extended.
19. Open the J 42435 in-line valve. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) . The tank should always contain some pressure and begin to vent.
20. Allow the CNG fuel tank to vent until the pressure gauge reads 0 kPa (0 psi). When the tank stops venting inspect the vent line or the HPL for a frozen fitting. The fitting will eventually thaw and fuel may continue to vent.
21. When the tank is completely vented remove the vent line from the fuel fitting.
22. Remove the fuel fitting from the fuel outlet port (4).
23. Remove the manual vent tool.
24. If the tank is to be re-used replace the high pressure lock-off. Refer to «High Pressure Lock-Off (HPL) Solenoid Replacement»(ref-185854-S31261704302005082900000) .

Fuel Tank Cleaning

Tools Required

J 44244 CNG Tank Support Harness. See Special Tools and Equipment .

1. Perform the «Fuel Pressure Relief Procedure»(ref-185854-S02905361662005082900000) .
2. Perform the «Fuel Tank Venting Procedure»(ref-185854-S17889565712005082900000) .
3. Perform the high pressure lock-off (HPL) removal procedure leaving the HPL installed into the tank finger-tight. Refer to «High Pressure Lock-Off (HPL) Solenoid Replacement»(ref-185854-S31261704302005082900000) .
4. Place the J 44244 (1) on the shop floor. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
5. Lower the CNG fuel tank (2) on top of the J 44244 (1). See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
6. Place the J 44244 support flap so that the HPL (3) protrudes through the flap. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
7. Place the J 44244 (1) straps around the CNG fuel tank placing the end strap over the HPL (3) and around the neck of the CNG fuel tank. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
8. Securely fasten the J 44244 straps (2) around the CNG fuel tank (1). See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) . Longer CNG fuel tanks will require the use of all the J 44244 straps. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
9. Connect the J 44244 to a suitable lifting device. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
10. Slowly raise the CNG fuel tank (1) until the HPL (2) is several inches above the ground ensuring that the HPL does not contact the floor during the lifting process.
11. Place a container (3) underneath the HPL (2) in order to collect any drained fluids.
12. Remove the HPL (2), allowing any fluids to drain completely from the CNG fuel tank.
13. Dispose of any collected fluids in a safe and approved manner.
14. Flush the inside of the CNG fuel tank using clean water.
15. Dry the inside of the CNG fuel tank using compressed air.
16. Install the HPL (2) finger-tight.
17. Slowly lower the CNG fuel tank (1) back to the ground ensuring the HPL does not contact the ground.
18. Remove the J 44244 (1) from the CNG fuel tank (2). See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
19. Complete the installation of the HPL into the tank and the tank into the vehicle by completing the installation steps as indicated in the «High Pressure Lock-Off (HPL) Solenoid Replacement»(ref-185854-S31261704302005082900000) .

Tools Required

1. J 45878 Combustible Gas Detector. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
2. J 45397-2 CNG Tank Lifting Tool. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
3. J 45529 CNG Tank Lifting Bar. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .

1. J 45878 Combustible Gas Detector. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
2. J 45397 CNG Dual Tank Lifting Kit. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
3. J 45529 CNG Tank Lifting Bar. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .

1. J 45878 Combustible Gas Detector. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
2. J 45397 CNG Dual Tank Lifting Kit. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
3. J 45529 CNG Tank Lifting Bar. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

1. J 45878 Combustible Gas Detector. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .
2. J 43602 HPL Crowfoot. See «Special Tools and Equipment»(ref-185854-S39958709232005082900000) .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

J 45878 Combustible Gas Detector. See Special Tools and Equipment .

Powertrain Control Module (PCM)

The PCM controls fuel delivery and for KL6 vehicles, determines which fuel system the engine is operating on. The PCM monitors various engine and vehicle functions to provide the correct amount of CNG or gasoline fuel under all operating conditions. This provides excellent driveability and fuel economy while maintaining reduced emission levels. When operating on CNG, the PCM grounds the AFO enable circuit. When the AFO enable circuit is grounded, the fuel injector control module (FICM) will sequentially operate the CNG fuel injectors. The PCM is not capable of operating the high current CNG fuel injectors. The PCM injector pulse width signals are received by the FICM and duplicate pulse width signals are generated by the FICM in order to operate the CNG injectors.

The PCM monitors 3 PWM signals from the FICM in order to determine CNG fuel rail pressure, CNG fuel rail temperature, and the diagnostic status of the FICM. The FICM monitors the CNG fuel rail pressure sensor, and the CNG fuel rail temperature sensor. This information is communicated to the PCM by dedicated PWM circuits. The FICM also performs internal diagnostics, and communicates this information by a dedicated PWM circuit. For further detail refer to Fuel Injector Control Module Description .

The PCM controls the Low Pressure Lock-Off (LPL) solenoids, and the High Pressure Lock-Off (HPL) solenoids. The PCM commands the HPL solenoids open for 1 second at every ignition ON, in order to prime the CNG fuel system. The PCM commands the HPLs, and the LPL open, when the engine is cranking or running on CNG.

When operating on gasoline, the PCM will turn the fuel indicator lamp ON. The fuel indicator lamp (FIL) is located within the headlamp switch assembly near the fuel gauge select switch. The FIL is also turned ON for a two-second bulb check whenever the ignition is turned ON. The fuel gauge select switch allows the vehicle operator the ability to request fuel gauge display of either fuel tank.

The PCM also determines the CNG fuel level. The PCM monitors the FTP and FTT sensors that are located on one of the CNG tank high pressure lock-off solenoids. The PCM performs a calculation of the CNG pressure and CNG temperature in order to determine an accurate CNG fuel level. On Bi-fuel (KL6) models the gasoline fuel level is determined by the PCM in a conventional manner using an in-tank variable resistor sensor.

For further PCM description refer to Powertrain Control Module (PCM) Description in Engine Controls in the G/H Van Service Manual.

FRP and FRT Sensor PWM Circuits

The fuel rail pressure and temperature sensor information is required by the PCM for fuel trim adjustment. The PCM does not have the ability to supply and monitor the FRP and FRT sensors. The FICM performs this task by supplying the FRP and FRT sensors a 5 volt reference, low reference and signal circuit. The signal voltage of the FRP and FRT sensors are converted into independent PWM signals. The PWM signals are sent to the PCM through dedicated circuits. The PCM converts the PWM signals into pressure and temperature values. The FICM also performs diagnosis of the FRP and FRT circuits as well as internal FICM diagnostic information. The FICM diagnostic information is converted into a PWM signal. The FICM PWM signal is sent to the PCM through a dedicated circuit.

The PCM controls fuel delivery and for KL6 vehicles, determines which fuel system operates the engine. The PCM monitors various engine and vehicle functions to provide the correct amount of CNG or gasoline fuel under all operating conditions. This provides excellent driveability and fuel economy while maintaining reduced emission levels. When operating on gasoline, the PCM will turn the fuel indicator lamp ON. The fuel indicator lamp (FIL) is located within the headlamp switch assembly near the fuel gauge select switch. The FIL is also turned ON for a two-second bulb check whenever the ignition is turned ON. The fuel gauge select switch allows the vehicle operator the ability to request fuel gauge display of either fuel tank.

Fuel Injector Control Module (FICM)

The PCM is connected to the FICM. The PCM is not capable of operating the high current CNG fuel injectors. The PCM injector pulse width signals are received by the FICM and duplicate pulse width signals are generated by the FICM in order to operate the CNG injectors. KL6 equipped vehicles utilize a FICM that contains internal relays. When operating on gasoline the internal relays allow the PCM injector pulse width to go directly to the gasoline injectors. Refer to Fuel Injector Control Module Description for more detailed description information.

Fuel Supply Components

The primary components of the CNG fuel SUPPLY system are as follows

1. Fuel Tanks
2. Fill Valve and Fill Line
3. High Pressure Lock-Off (HPL) solenoids
4. Fuel Tank Pressure (FTP) sensor
5. Fuel Tank Temperature (FTT) sensor
6. Fuel Lines
7. In-line Fuel Filter
8. Low Pressure Lock-Off (LPL) solenoid
9. Fuel Rail

Fuel Tanks

The CNG Fuel Tanks are constructed of high-strength steel covered with a two-stage epoxy coating finish. A high pressure lock-off solenoid is threaded into the end of each fuel tank and is used to prevent fuel flow during non-cranking or running engine conditions. The fuel tanks also have a protective cover. The cover is designed to protect the tank from road debris.

On passenger and cargo vans the fuel tanks are mounted in tandem, transverse behind the rear axle, under the vehicle. On cutaway vans the fuel tanks are mounted in tandem, parallel to the vehicle frame, behind the rear axle. Dedicated equipped vehicles (KL8) also utilize a third, mid-frame mounted tank that is located in place of the gasoline fuel tank.

Federal Government Regulations require that the fuel tank and brackets be inspected every three years or 60 000 km (36,000 miles), 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.

Fill Valve and Fill Line

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. The fill valve is mounted behind the fuel filler door. Refer to the owners manual supplement for 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 a line union check valve and is sealed at all connections with an O-ring.

In the event of fill valve leakage, the line union check valve is designed to minimize the amount of CNG fuel leakage.

High Pressure Lock-Off (HPL) Solenoids

The HPL is a normally closed, solenoid valve. The HPL solenoids, and a low pressure lock-off (LPL) solenoid in the fuel line, prevent fuel flow. The PCM commands ONLY the HPLs open for 1 second at EVERY ignition ON in order to prime the CNG fuel system. The CNG prime pulse is performed in order to allow the fuel tank pressure (FTP) sensor to monitor the amount of fuel pressure in the fuel line. The PCM commands BOTH the HPLs and the LPL open when engine RPM indicates that the engine is cranking or running on CNG.

Fuel Tank Pressure (FTP) Sensor

The FTP sensor is a pressure transducer. The PCM supplies about 5 volts on the FTP reference circuit. The PCM also supplies a signal and ground circuit to the FTP. When the fuel tanks are full (high pressure) a high voltage signal will be monitored by the PCM. The FTP sensor is threaded into one of the rear fuel tank HPL solenoids.

The volume of CNG will vary with temperature and pressure. Accurate CNG fuel level cannot be determined by pressure only. In order to compensate for the different volume factors a fuel tank temperature (FTT) sensor is mounted within the HPL. The PCM monitors the FTT sensor and performs a calculation on the FTP voltage vs. the in-tank temperature. The PCM will then display the temperature corrected fuel level.

The CNG FTP sensor should not be confused with the gasoline fuel tank pressure (FTP) sensor that is utilized for Evaporate (EVAP) emissions monitoring.

Fuel Tank Temperature (FTT) Sensor

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

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

The volume of CNG will vary with temperature and pressure. Accurate CNG fuel level cannot be determined by pressure only. In order to compensate for the different volume factors a fuel tank temperature (FTT) sensor is mounted within the HPL. The PCM monitors the FTT sensor and performs a calculation on the FTP voltage vs. the in-tank temperature. The PCM will then display the temperature corrected fuel level.

Fuel Lines

The CNG fuel system uses different fuel line types. The type used is dependent upon the pressure the fuel line is required 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 that are specific for gaseous fuel operation. These O-rings must be replaced with the correct replacement part whenever a line is opened.

Intermediate Pressure Fuel Hose

The intermediate pressure fuel hose assemblies are unique flexible lines for connection at fuel injector pressures. The individual lines connect using flared fittings.

When installing 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.

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

In-line Fuel Filter

The in-line fuel filter is located under the vehicle between the high pressure regulator and the low pressure lock-off (LPL) solenoid. The filter is serviced at regular intervals.

Low Pressure Lock-Off (LPL)

The HPL is a normally closed, solenoid valve. The solenoid provides a fuel shut-off to the fuel rails. The LPL solenoid is mounted to the right hand fuel rail. The LPL is only commanded ON when engine RPM indicates the engine is cranking or running on CNG.

Fuel Rail

The CNG fuel rails are constructed of aluminum and are mounted on either side of the intake manifold. Fuel enters the right fuel rail from the LPL solenoid that is mounted to the rail. A crossover fuel line connects the two fuel rails. The fuel rails are mounted in the same location as the gasoline fuel rails on KL8 equipped vehicles. The fuel rails are mounted slightly above the gasoline fuel rails on KL6 equipped vehicles. KL6 vehicles also utilize an injector tee in order to allow both fuels to inject into the same cylinder.

Fuel Metering Components

The primary components of the CNG fuel METERING system are as follows

1. High Pressure Regulator (HPR)
2. CNG Fuel Injectors
3. Fuel Rail Pressure Sensor
4. Fuel Rail Temperature Sensor

High Pressure Regulator (HPR)

The HPR is supplied with fuel from the CNG fuel tank at up to 24821 kPa (3600 psi) through high pressure stainless steel lines. The HPR reduces fuel pressure to around 1241 kPa (180 psi). The pressure drop within the regulator causes fuel temperature to drop. The HPR is connected to the vehicle engine cooling system in order to prevent HPR freeze-up. The outlet of the HPR is the injector pressure stage. Fuel flows out of the HPR and through the inline filter and into the low pressure lock-off (LPL) solenoid. The HPR contains an over-pressure relief device (PRD) which will not allow pressure above 1896 kPa (275 psi) on the output stage of the HPR. The HPR has an internal, serviceable 40 micron filter. This filter must be serviced periodically.

Gaseous Fuel Injectors

The gaseous fuel injectors are pulse-width modulated and sequentially fired. The injector voltage is supplied by a fuse. The FICM controls the ground path. KL6 vehicles utilize an injector tee in order to allow both fuels to inject into the same cylinder. KL8 vehicles mount the injectors directly into the intake manifold port.

Fuel Rail Pressure Sensor

The fuel rail pressure (FRP) sensor is a pressure transducer. The FICM supplies about 5 volts on the FRP sensor reference circuit. The FICM also supplies a signal and ground circuit to the FRP sensor. When fuel pressure is high the signal voltage is high. The FRP sensor data is transmitted to the PCM through a PWM signal circuit. The FRP signal is used by the PCM for fuel trim.

Fuel Rail Temperature Sensor

The fuel rail temperature (FRT) sensor is a thermistor. The FRT thermistor has high resistance when cold and low resistance when hot. The FICM supplies about 5 volts to the FRT sensor signal circuit. When the FRT sensor is cold its resistance is high and the signal voltage is high. As the FRT sensor warms and resistance drops, less signal voltage is monitored by the FICM. The FRT sensor data is transmitted to the PCM through a PWM signal circuit. The FRT signal is used by the PCM in order to adjust fuel trim.

Bi-Fuel (KL6) CNG System Operation

The primary fuel source of a Bi-fuel vehicle is compressed natural gas (CNG). The vehicle will only switch-over to gasoline operation if one of the following conditions is present

1. The fuel tank pressure sensor indicates CNG fuel pressure is below 896 kPa (130 psi).
2. Every 100th start the vehicle will start and run briefly on gasoline. After this, a switch-over to CNG will occur during the first decel condition.
3. A system fault is detected by the PCM or FICM.
4. The engine cranks for 5 seconds and fails to start on CNG.

60 Day Cycle

It is recommended that every 60 days the vehicle be cycled between CNG and gasoline. This ensures the gasoline fuel system stays in good working condition and also accommodates for seasonal changes in gasoline formulation. Perform the following steps every 60 days.

1. With the vehicle operating on CNG check and fill the gasoline level.
2. Operate the vehicle until the CNG fuel tank is empty and the vehicle switches over to gasoline operation.
3. Operate the vehicle until the gasoline tank is near empty.
4. Refill both fuel tanks.
5. The vehicle will switch-over to CNG operation.
6. Repeat procedure in 60 days.

Fuel Indicator Lamp (FIL)

The fuel indicator lamp (FIL) is contained within the headlamp switch assembly. The fuel indicator lamp indicates which fuel system the vehicle is operating on. The PCM controls the operation of the fuel indicator lamp. The fuel indicator lamp illuminates only when the engine is operating on gasoline. The fuel indicator lamp will also illuminate for several seconds during start-up as a bulb check.