Symptoms - Engine Controls
| Important Preliminary Checks | Action |
|---|
| Before performing Symptom diagnosis | Before performing Symptom based diagnosis you must perform the Diagnostic System Check - Alternative Fuels (Engine Controls) . The System Check will determine the following: The FICM, PCM and the MIL are operating correctly. There are no DTCs stored. Scan tool data is within normal operating range. Several of the Symptom diagnostic tables require that a Visual and Physical Check be performed. Always perform a Visual and Physical Check before using a Symptom diagnostic table. |
| Visual and Physical Checks | Inspect the FICM and PCM ground connections for being clean, tight and in the correct location. Inspect the PCM for the correct CNG calibration. Program the PCM if necessary. Inspect the FICM for the proper part number. Bi-fuel (KL6) and dedicated (KL8) CNG equipped vehicles utilize unique FICM's that are not interchangeable. Inspect the vacuum hoses for leaks, restrictions and proper connection as shown on the vehicle emission control information (VECI) label. Inspect for any type of fuel leak or fuel line restriction. Inspect for air leaks at all areas of the intake manifold sealing surfaces. Inspect the ignition wires for the following conditions: Cracking Hardness Proper routing Carbon tracking Inspect vehicle wiring for the following: Proper connection Pinches Cuts |
| Symptoms | Verify the customer concern. Locate the Symptom table that indicates the customers concern. Test or Inspect for the items indicated for that symptom. The following Symptom tables are located in this section: Intermittent Conditions Hard Start Surges/Chuggles Lack of Power, Sluggishness, or Sponginess Hesitation, Sag, Stumble Cuts Out, Misses Poor Fuel Economy Poor Fuel Fill Quality Rough, Unstable, or Incorrect Idle and Stalling Dieseling, Run-On Backfire |
Important Preliminary Checks
System Description
The powertrain control module (PCM) controls the fuel system while the vehicle is operating on CNG. The PCM receives signals from various engine sensors and determines the correct amount of fuel required by the engine. The fuel is stored in cylindrical fuel tanks. A full tank can contain fuel at 24,820 kPa (3600 psi). A high pressure lock-off (HPL) solenoid in each tank and a low pressure lock-off (LPL) solenoid in the fuel line prevent fuel flow. The PCM commands ONLY the HPL's open for 1 second at every ignition ON for a CNG prime pulse. The CNG prime pulse is performed in order to charge the fuel line and also allows the fuel tank pressure (FTP) sensor to monitor the amount of fuel pressure in the tanks. The PCM commands BOTH the HPL's and the LPL open when engine RPM indicates the engine is cranking or running on CNG.
This fuel delivery system utilizes a high pressure regulator (HPR) in order to lower the fuel pressure from tank pressure down to an injector delivery pressure.
When the PCM commands the HPL's open, fuel begins to flow through the HPR. The HPR reduces pressure to between 896-1379 kPa (130-200 psi). The fuel exiting the HPR flows through the intermediate fuel line to the fuel rail mounted low pressure lock-off (LPL) solenoid. Fuel flows out of the LPL and through the fuel rails to the injectors.
Test Description
The number below refers to the step number on the diagnostic table.
- 2: This step verifies that the HPL solenoid and the FTP sensor are functioning. A fuel tank pressure value that decreases while the engine is operating indicates the HPL is not opening or the manual tank valve is closed.
- 3: This step verifies the FRP sensor is displaying the correct fuel pressure.
- 4: This step tests for a leak in the fuel system between the low pressure lock-off (LPL), and the fuel injectors. The fuel pressure should remain constant during the test.
- 5: This step tests the HPR output pressure. If the fuel pressure is within the specified values, then the HPR, fuel lines, and filters are OK.
- 6: This step tests the operation of the HPL relay.
- 9: This step tests the operation of the LPL relay.
- 13: This step verifies that a fuel filter is not the cause of the condition. If the fuel pressure is within the specified range after the fuel filter replacement, then a plugged filter was the cause of the condition.
| Step | Action | Value(s) | Yes | No |
|---|
| Schematic Reference: Engine Controls Schematics |
| 1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
| 2 | Connect the vehicle to a CNG dispensing station and verify that the CNG fuel tank is at least 1/3 full. Fill CNG fuel tank if necessary. Observe the fuel tank pressure (FTP) sensor data display with a scan tool. Attempt to start and idle the engine. Does the FTP sensor display a steady pressure at or above the specified value? | 8274 kPa (1200 psi ) | Go to Step 3 | Go to Step 6 |
| 3 | Attempt to start and idle the engine. Idle the engine until normal operating temperature is obtained. IMPORTANT: If the engine will not start on CNG use the pressure values observed during cranking and proceed directly to the Step question. Observe and record the FRP sensor display with a scan tool. Compare the recorded scan tool display pressure values to the value range specified. Is the FRP sensor value within the specified range? | 896-1379 kPa (130-200 psi) | Go to Step 4 | Go to Step 8 |
| 4 | Turn OFF the ignition. Turn ON the ignition with the engine OFF. Command the LPL solenoid ON and OFF with a scan tool in order to charge the fuel rail with pressure. Monitor the fuel rail pressure for 5 minutes after commanding the LPL solenoid closed. Does the fuel rail pressure drop more than the specified value? | 21 kPa (3 psi) | Go to Step 10 | Go to Step 5 |
| 5 | IMPORTANT: If the engine will not start on CNG use the pressure values observed during cranking and proceed directly to the Step question. Observe the FRP sensor display with the scan tool while cranking the engine. Idle the engine until normal operating temperature is obtained. IMPORTANT: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless the fluctuations become excessive. Observe and record the FRP sensor display with a scan tool at engine idle. Observe and record the pressure indicated by the FRP sensor display during engine load by performing the following steps: Apply the parking brake. Firmly apply and hold the brake pedal. Place the vehicle in forward gear. Observe the pressure while depressing the throttle to 75 percent or greater for a maximum of 10 seconds. Allow the engine to idle for a minimum of two minutes in order to cool the transmission. Compare the recorded pressure values to the value range specified. Are all of the fuel pressure values within the specified range? | 896-1379 kPa (130-200 psi) | Go to Intermittent Conditions | Go to Step 12 |
| 6 | Turn ON the ignition with the engine OFF. Command the HPL ON and OFF with a scan tool. Listen for operation of the HPLs. Can operation of the HPLs be heard? | | Go to Step 7 | Go to Fuel Lock-Off Relay Diagnosis |
| 7 | Ensure the manual tank valves are fully open by turning the screws fully counter clockwise. Did you have to open the manual tank valves? | | Go to Step 2 | Go to Step 14 |
| 8 | Is the fuel pressure greater than the specified value? | 1379 kPa (200 psi) | Go to Step 15 | Go to Step 9 |
| 9 | Turn the ignition ON with the engine OFF. Command the low pressure lock-off (LPL) ON and OFF with a scan tool. Listen for operation of the LPL. Can operation of the LPL be heard? | | Go to Step 12 | Go to Fuel Lock-Off Relay Diagnosis |
| 10 | Inspect for a fuel system leak between the LPL solenoid and the CNG fuel injectors. Replace any leaking components as necessary. Did you find and correct the condition? | | Go to Step 16 | Go to Step 11 |
| 11 | Raise the CNG fuel rails, lines and injectors as an assembly. Refer to Fuel Rail Assembly Replacement (KL6) or Fuel Rail Assembly Replacement (KL8) . Command the LPL ON with a scan tool. Locate and replace the leaking CNG fuel injector. Refer to Fuel Injector Replacement . Did you complete the replacement? | | Go to Step 16 | |
| 12 | Inspect the fuel line between the HPL and the HPR and the fuel line between the HPR and the LPL for the following: Kinks Bends Damage Obstruction An obstructed fuel line may be cool or frosted near the obstruction when fuel flows through the line. Repair or replace components as necessary. Did you find and correct the condition? | | Go to Step 16 | Go to Step 13 |
| 13 | Relieve the CNG fuel system pressure. Refer to Fuel Pressure Relief Procedure . Replace the CNG In-line filter. Refer to Fuel Filter Replacement (Passenger/Cargo) or Fuel Filter Replacement (Cutaway) . Replace the HPR filter. Refer to High Pressure Regulator (HPR) Filter Replacement . IMPORTANT: If the engine will not start on CNG use the pressure values observed during cranking and proceed directly to the Step question. Observe the FRP sensor display with a scan tool while cranking the engine. Idle the engine until normal operating temperature is obtained. IMPORTANT: Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless the fluctuations become excessive. Observe and record the FRP sensor display at engine idle. Observe and record the FRP sensor display during engine load by performing the following steps: Apply the parking brake. Firmly depress and hold the brake pedal. Place the vehicle in forward gear. Observe the pressure while depressing the throttle to 75 percent or greater for a maximum of 10 seconds. Allow the engine to idle for a minimum of two minutes in order to cool the transmission. Compare the recorded pressure values to the value range specified. Are all fuel pressure values within the specified range? | 896-1379 kPa (130-200 psi) | Go to Step 16 | Go to Step 15 |
| 14 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | | Go to Step 16 | |
| 15 | Replace the HPR. Refer to High Pressure Regulator (HPR) Replacement (Passenger/Cargo) or High Pressure Regulator (HPR) Replacement (Cutaway) . Did you complete the replacement? | | Go to Step 16 | |
| 16 | Relieve the CNG fuel system pressure. Refer to Fuel Pressure Relief Procedure . Turn OFF the ignition. Remove all remaining test equipment. Start and idle the engine. Inspect for CNG fuel system leaks with the J 41416 Ultrasonic Leak Detector and Snoop® or soapy water. Repair any leaks as necessary. Clear DTC information with a scan tool from the PCM. Turn the ignition OFF and wait 30 seconds. Start the engine and operate the vehicle. Observe the MIL. Observe vehicle performance and driveability. Does the vehicle operate on CNG with normal driveability and no MIL illumination? | | System OK | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
| IMPORTANT |
|---|
| If the engine will not start on CNG use the pressure values observed during cranking and proceed directly to the Step question. |
| IMPORTANT |
|---|
| If the engine will not start on CNG use the pressure values observed during cranking and proceed directly to the Step question. |
| IMPORTANT |
|---|
| Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless the fluctuations become excessive. |
| IMPORTANT |
|---|
| If the engine will not start on CNG use the pressure values observed during cranking and proceed directly to the Step question. |
| IMPORTANT |
|---|
| Rhythmic pressure fluctuation of 10-20 psi is normal. A defective HPR is not indicated unless the fluctuations become excessive. |
The numbers below refer to the step numbers on the diagnostic table.
- 3: This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
- 4: This step determines if all of the fuel injectors are within 0.5 ohms of each other. If the highest resistance value is within 0.5 ohms of the lowest resistance value, then all of the fuel injector coil windings are OK.
- 5: This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.
| Step | Action | Values | Yes | No |
|---|
| Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views |
| 1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
| 2 | Observe the engine coolant temperature (ECT) with a scan tool. Is the ECT value within the specified range? | 10-32° C (50-90° F) | Go to Step 3 | Go to Step 4 |
| 3 | NOTE: Use care in removing the fuel injectors in order to prevent damage to the fuel injector electrical connector pins or the fuel injector nozzles. Do not immerse the fuel injector in any type of cleaner. The fuel injector is an electrical component and may be damaged by this cleaning method. IMPORTANT: Calibrate the DMM and test leads to 0 ohms in order to prevent misdiagnosis. Measure the resistance of each compressed natural gas (CNG) fuel injector with a DMM. Refer to Testing for Continuity in Wiring Systems in the G/H Van Service Manual.Do any of the fuel injectors display a resistance outside the specified range? | 4.56-5.04 ohms | Go to Step 6 | Go to Diagnostic Aids |
| 4 | NOTE: Use care in removing the fuel injectors in order to prevent damage to the fuel injector electrical connector pins or the fuel injector nozzles. Do not immerse the fuel injector in any type of cleaner. The fuel injector is an electrical component and may be damaged by this cleaning method. Measure the resistance of each CNG fuel injector with a DMM. Refer to Testing for Continuity in Wiring Systems in the G/H Van Service Manual. Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to, or less than, the specified value? | 0.5 ohms | Go to Diagnostic Aids | Go to Step 5 |
| 5 | Add all of the CNG fuel injector resistance values, to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors, to obtain an average resistance value. Subtract the lowest, and the highest, individual fuel injector resistance values from the average resistance value. Replace the CNG fuel injector that displays the greatest resistance difference, above or below the average. Refer to Fuel Injector Replacement . Did you complete the replacement? | | Go to Step 7 | |
| 6 | Replace the fuel injector or fuel injectors that are out of the specified range. Refer to Fuel Injector Replacement . Did you complete the replacement? | | Go to Step 7 | |
| 7 | Operate the system in order to verify the repair. Did you correct the condition? | | System OK | Go to Step 2 |
| NOTE |
|---|
| Use care in removing the fuel injectors in order to prevent damage to the fuel injector electrical connector pins or the fuel injector nozzles. Do not immerse the fuel injector in any type of cleaner. The fuel injector is an electrical component and may be damaged by this cleaning method. |
| IMPORTANT |
|---|
| Calibrate the DMM and test leads to 0 ohms in order to prevent misdiagnosis. |
| NOTE |
|---|
| Use care in removing the fuel injectors in order to prevent damage to the fuel injector electrical connector pins or the fuel injector nozzles. Do not immerse the fuel injector in any type of cleaner. The fuel injector is an electrical component and may be damaged by this cleaning method. |
The numbers below refer to the step numbers on the diagnostic table.
- 3: The fuel pressure should be within the specified range. Refer to Fuel System Diagnosis if the fuel pressure is not within the specified range.
- 5: If the pressure drop value for each fuel injector is within 14 kPa (2.0 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.
| Step | Action | Values | Yes | No |
|---|
| 1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
| 2 | Did you perform the Fuel Injector Coil Test? | | Go to Step 3 | Go to Fuel Injector Coil Test |
| 3 | Start and idle the engine. Observe the fuel rail pressure sensor parameter with a scan tool. Is the fuel pressure within the specified range? | 896-1379 kPa (130-200 psi) | Go to Step 4 | Go to Fuel System Diagnosis |
| 4 | Turn OFF the ignition. Turn ON the ignition, with the engine OFF. Monitor the fuel rail pressure sensor parameter with a scan tool. Does the fuel rail pressure remain constant? | | Go to Step 5 | Go to Fuel System Diagnosis |
| 5 | NOTE: Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding. Turn OFF the ignition. Connect the J 39021 Fuel Injector Tester to a fuel injector. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position. Turn ON the ignition, with the engine OFF. Record the fuel pressure indicated by the fuel rail pressure sensor after the fuel pressure stabilizes. This is the first pressure reading. IMPORTANT: Record the fuel pressure value immediately after the CNG fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the CNG fuel injector by depressing the Push to Start Test button on the fuel injector tester. Record the fuel pressure indicated by the fuel rail pressure sensor. This is the second fuel pressure reading. Repeat steps 1 through 6 for each fuel injector. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is more than the average pressure drop or less than the average pressure drop by the specified value? | 14 kPa (2.0 psi) | Go to Step 6 | Go to Symptoms - Engine Controls |
| 6 | Replace the affected CNG fuel injector. Refer to Fuel Injector Replacement . Did you complete the replacement? | | Go to Step 7 | |
| 7 | Operate the vehicle in order to verify the repair. Does a driveability condition still exist? | | Go to Symptoms - Engine Controls | System OK |
| NOTE |
|---|
| Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding. |
| IMPORTANT |
|---|
| Record the fuel pressure value immediately after the CNG fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. |
Fuel Injector Balance Test Procedure
The numbers below refer to the step numbers on the diagnostic table.
- 3: The fuel pressure should be within the specified range. Refer to Fuel System Diagnosis if the fuel pressure is not within the specified range.
- 4: The fuel pressure should reach a steady value. Refer to Fuel System Diagnosis if the fuel pressure does not stabilize.
- 5: If the pressure drop value for each fuel injector is within 14 kPa (2.0 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.
| Step | Action | Values | Yes | No |
|---|
| 1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
| 2 | Did you perform the Fuel Injector Coil Test? | | Go to Step 3 | Go to Fuel Injector Coil Test |
| 3 | Start and idle the engine. Observe the fuel rail pressure sensor parameter with a scan tool. Is the fuel pressure within the specified range? | 896-1379 kPa (130-200 psi | Go to Step 4 | Go to Fuel System Diagnosis |
| 4 | Turn OFF the ignition. Turn ON the ignition, with the engine OFF. Monitor the fuel rail pressure sensor parameter with a scan tool. Does the fuel rail pressure remain constant? | | Go to Step 5 | Go to Fuel System Diagnosis |
| 5 | NOTE: Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding. With a scan tool, select the Fuel Injector Balance Test function, within the Special Functions menu. Select an injector to be tested. Press Enter. This will prime the fuel system. Record the fuel pressure indicated by the fuel pressure sensor after the fuel rail pressure stabilizes. This is the 1st pressure reading. IMPORTANT: Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. Energize the fuel injector by depressing the Pulse Injector button on the scan tool. This will energize the injector and decrease the fuel pressure. Record the fuel pressure indicated by the fuel rail pressure sensor after the fuel injector has stopped pulsing. This is the 2nd pressure reading. Press Enter again to bring you back to the Select Injector screen. Repeat for each fuel injector. Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by the specified value? | 14 kPa (2.0 psi) | Go to Step 6 | Go to Symptoms - Engine Controls |
| 6 | Replace the affected fuel injector. Refer to Fuel Injector Replacement . Did you complete the replacement? | | Go to Step 7 | |
| 7 | Operate the vehicle in order to verify the repair. Does a driveability condition still exist? | | Go to Symptoms - Engine Controls | System OK |
| NOTE |
|---|
| Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding. |
| IMPORTANT |
|---|
| Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value. |
Fuel Injector Balance Test Procedure
