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Home >> Chevy Truck >> 2013 >> Express 3500 V8-6.0L CNG >> Repair and Diagnosis >> Powertrain Management >> Tune-up and Engine Performance Checks >> Fuel Pressure >> Testing and Inspection >> Fuel System Diagnosis (K07UFP)

Fuel System Diagnosis (K07UFP)




Fuel System Diagnosis (LC8\K07\UFP)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The engine control module (ECM) enables the fuel pump relay when the ignition switch is turned ON. The ECM will disable the fuel pump relay within 30 seconds unless the ECM detects ignition reference pulses. The ECM continues to enable the fuel pump relay as long as ignition reference pulses are detected. The liquid propane control module receives the signal voltage from the fuel pump relay and enables the LPG fuel system. The liquid propane control module controls the primary fuel pump relay, LPG cut-off solenoid valve - front relay, and LPG cut-off solenoid valve - purge. When the ignition is initially ON the liquid propane control module turns on the wait to start lamp and supplies voltage to the LPG cut-off solenoid valve - purge for 5-8 seconds. The module also turns on the primary fuel pump and LPG cut-off solenoid valve - front relay for 30 seconds without the engine running. When the engine is running only the relays are energized.

Reference Information

Description and Operation

Fuel System Description (LC8\K07\UFP) Description and OperationFuel System Description (LC8\FHZ) Description and OperationFuel System Description (LC8\K07\UFM) Description and OperationFuel System Description (Without LC8) Description and Operation

Schematic Reference

Engine Controls Schematics [1][2]Electrical Diagrams

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Electrical Information Reference

* Circuit Testing Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Programming and Relearning

Diagnostic Aids

A hot soak test is a test conducted before and/or after a repair. Vehicles that have extended cranking time, hard start, rough idle, or misfires after starting when hot should have this test performed. A hot soak test will assist in determining the following:

* If the concentric hoses inner liquid supply lines are sealed at all points

* If the return valve is working properly

* If there are injectors leaking fuel into the cylinder port.

1. Drive the vehicle or run the vehicle with the hood closed until engine temperature is at full operating temperature.

2. Park the vehicle with the hood closed. Allow the vehicle to sit for 20 minutes.

3. Within 25 minutes, Turn ON the ignition and wait for the Wait to Start indicator to turn OFF.

4. Verify the engine will start within 3 seconds and idles smooth.

• If the engine does not start within 3 seconds or idles rough
Inspect for the following conditions:

* An inner liquid supply line that may not be sealed in the port of the liquid propane delivery module or injector rail.

* A return solenoid valve that may be malfunctioning, closed and will not open, restricted, or obstructed.

* A leaking injector, hot soak the vehicle and test for a propane smell at the intake manifold inlet.

* A weak fuel pump may cause a hard starting condition, refer to Circuit/System Verification.

• If the engine starts within 3 seconds and idles smooth

5. All OK

Circuit/System Verification

Note:

* Repair all fuel system related DTCs before performing this diagnostic, unless instructed here from a DTC diagnostic.

* Inspect the fuel system for damage or external leaks before proceeding.

* Verify that adequate fuel is in the fuel tanks before proceeding.

1. Ignition OFF, all vehicle systems OFF, install a 0-300 psi fuel pressure gauge at the liquid propane delivery module, refer to Fuel Pressure Gauge Installation and Removal Testing and Inspection. It may take up to 2 minutes for all vehicle systems to power down.

2. Record the pressure reading on the gauge.

3. Ignition ON.

4. Verify there is an audible click from the fuel control solenoids and the in tank fuel pump is ON for 30 seconds.

• If NO audible click from the fuel control solenoids or the in tank fuel pump is OFF
Refer to the Liquid Propane Control Module Test

• If an audible click from the fuel control solenoids and the in tank fuel pump is ON

5. Ignition OFF, all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.

Note:

* The liquid propane control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the liquid propane control module will turn the fuel pump ON and open both the purge valve and fuel cut off valve for the first 5-8 seconds. After 5-8 seconds the purge valve closes while the cut off valve and fuel pump run for 30 seconds total.

* Pressure differences may change slightly depending on altitude and ambient temperatures

6. Ignition ON.

7. Verify the fuel pressure increases 20-35 psi in the first 5-8 seconds of key ON and then increases an additional 10-15 psi for 30 seconds.

• If the pressure does not increase 20-35 psi
Refer to the Circuit/System Testing

• If the pressure increased 20-35 psi and then did not increase an additional 10-15 psi
Refer to Circuit/System Testing

• If the pressure increased greater than 60 psi
Test or replace the liquid propane delivery module.

• If the pressure increased 20-35 psi and then increased an addition 10-15 psi

8. All OK

Circuit/System Testing

1. Ignition OFF, all vehicle systems OFF, Disconnect the in-line harness connector at the liquid propane delivery module. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 ohms between the harness side of the in-line connector liquid propane delivery module ground circuit terminal 4 and ground.

• If 10 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

3. Test for 1 V or less between the following terminals on the harness side of the in-line connector and ground.

* Terminal 1 primary fuel pump voltage supply circuit

* Terminal 2 LPG cut-off solenoid valve - front and transfer pump voltage supply circuit

* Terminal 3 LPG cut-off solenoid valve - purge control circuit

• If greater than 1 V
Refer to the appropriate test

* Terminal 1, Primary Fuel Pump Relay Testing

* Terminal 2, LPG Cut-Off Solenoid Valve - Front Relay Testing

* Terminal 3, LPG Cut-Off Solenoid Valve - Purge Testing

* All terminals, Liquid Propane Control Module Testing

• If 1 V or less

4. Connect a test lamp on the harness side of the in-line between the LPG cut-off solenoid valve - purge control circuit terminal 3 and ground.

Note: The liquid propane control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the liquid propane control module will turn the fuel pump ON and open both the purge valve and fuel cut off valve for the first 5-8 seconds. After 5-8 seconds the purge valve closes while the cut off valve and fuel pump run for 30 seconds total.

5. Ignition ON.

6. Verify the test lamp illuminates for 5-8 s and then turns OFF.

• If the test lamp does not illuminate or remains illuminated
Refer to LPG cut-off solenoid valve - purge Testing.

• If the test lamp illuminates for 5-8 s and turns OFF.

7. Ignition OFF, all vehicle systems OFF, connect a test lamp on the harness side of the in-line between the LPG cut-off solenoid valve - front voltage supply circuit terminal 2 and ground. It may take up to 2 minutes for all vehicle systems to power down.

8. Ignition ON.

9. Verify the test lamp illuminates for 30 s.

• If the test lamp does not illuminate
Refer to LPG Cut-Off Solenoid Valve - Front Relay Testing.

• If the test lamp illuminates

10. Ignition OFF, all vehicle systems OFF, connect a test lamp on the harness side of the in-line between the primary fuel pump voltage supply circuit terminal 1 and ground.

11. Ignition ON.

12. Verify the test lamp illuminates for 30 s.

• If the test lamp does not illuminate
Refer to Primary Fuel Pump Relay Testing

• If the test lamp illuminates
Test or replace the liquid propane delivery module.

Liquid Propane Control Module Test

1. Ignition OFF, disconnect the X1 harness connector at the liquid propane control module.

2. Connect a test lamp between the fuel pump signal circuit J2 and ground.

3. Ignition ON, command the fuel pump relay ON and OFF with a scan tool,

4. Verify the test lamp turns ON and OFF with each command.

• If the test lamp is always OFF or always ON
Refer to Fuel Pump Electrical Circuit Diagnosis (FPCM) Fuel Pump Electrical Circuit DiagnosisFuel Pump Electrical Circuit Diagnosis (LC8\K07\UFP) Testing and InspectionFuel Pump Electrical Circuit Diagnosis (LC8\FHZ) Testing and InspectionFuel Pump Electrical Circuit Diagnosis (Without FPCM) Fuel Pump Electrical Circuit DiagnosisFuel Pump Electrical Circuit Diagnosis (LC8\K07\UFM) Testing and Inspection

• If the test lamp turns ON and OFF with each command

5. Test for 10 ohms or less between the liquid propane control module ground circuit K2 and ground.

• If 10 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

6. Connect a test lamp between the liquid propane control module voltage supply circuit H1 and ground.

7. Verify the test lamp illuminates

• If the test lamp does not illuminate

Note: Verify the in-line fuse is not open

1. Connect a test lamp between the voltage supply circuit at the in-line fuse holder and ground.

2. Verify the test lamp illuminates.

• If the test lamp does not illuminate, repair the open/high resistance in the voltage supply circuit between the fuse holder and battery.

• If the test lamp illuminates, repair the open/high resistance in the voltage supply circuit between the fuse holder and the liquid propane control module.

• If the fuse is opened, test the voltage supply circuit and the following components for a short to ground

* Liquid Propane Control Module

* Primary Fuel Pump

* Secondary Fuel Pump

* Scavenge Pump

• If the test lamp illuminates

8. Ignition OFF, connect the X1 harness connector at the liquid propane control module.

9. Disconnect the in-line harness connector at the liquid propane delivery module.

10. Connect a test lamp between liquid propane delivery module ground circuit terminal 4 and the supply valve voltage supply circuit terminal 2.

11. Ignition OFF.

12. Verify the test lamp does not illuminate.

• If the test lamp illuminates
Refer to LPG Cut-Off Solenoid Valve - Front Testing.

• If the test lamp turn does not illuminate

13. Ignition ON.

14. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Refer to LPG Cut-Off Solenoid Valve - Front Relay Testing.

• If the test lamp illuminates

15. Ignition OFF, Connect the in-line harness connector to the liquid propane delivery module.

16. Ignition ON.

17. Verify the LPG cut-off solenoid valve - front operates.

• If the LPG cut-off solenoid valve - front does not operate
Test or replace the liquid propane delivery module.

• If the LPG cut-off solenoid valve - front operates

18. Ignition OFF, disconnect the in-line harness connector at the liquid propane delivery module.

19. Connect a test lamp between liquid propane delivery module ground circuit terminal 4 and the primary fuel pump supply circuit terminal 1.

20. Ignition OFF.

21. Verify the test lamp does not illuminate.

• If the test lamp illuminates
Refer to Primary Fuel Pump Relay Testing

• If the test lamp turn does not illuminate

22. Ignition ON.

23. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Refer to Primary Fuel Pump Relay Testing

• If the test lamp illuminates

24. Ignition OFF, Connect the in-line harness connector to the liquid propane delivery module.

25. Ignition ON.

26. Verify the fuel pump operates.

• If the primary fuel pump does not operate
Test or replace the liquid propane delivery module

• If the primary fuel pump operates

27. Ignition OFF, disconnect the in-line harness connector at the liquid propane delivery module.

28. Connect a test lamp between liquid propane delivery module ground circuit terminal 4 and the purge control circuit terminal 3.

Note: The liquid propane control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the liquid propane control module will turn the fuel pump ON and open both the purge valve and fuel cut off valve for the first 5-8 seconds. After 5-8 seconds the purge valve closes while the cut off valve and fuel pump run for 30 seconds total.

29. Ignition ON.

30. Verify the test lamp illuminates for 5-8 seconds and then turns OFF.

• If the test lamp does not illuminate for 5-8 s and then turn OFF
Refer to LPG cut-off solenoid valve - purge Testing.

• If the test lamp illuminates for 5-8 s and then turns OFF

31. Connect the in-line harness connector at the liquid propane delivery module.

32. Ignition ON.

33. Verify the purge control solenoid operates.

• If the purge control solenoid does not operate
Test or replace the liquid propane delivery module.

• If the LPG cut-off solenoid valve - purge operates

34. All OK

Fuel Pump Relay Test - Primary

1. Remove the primary fuel pump relay.

2. Connect a test lamp between the voltage supply circuit terminal E and ground.

3. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Repair the open or high resistance in the circuit

• If the test lamp illuminates

4. Connect a test lamp between the voltage supply circuit terminal F and ground.

5. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Repair the open or high resistance in the circuit

• If the test lamp illuminates

6. Connect a test lamp between the voltage supply circuit terminal E and the signal circuit terminal D.

7. Ignition OFF.

8. Verify the test lamp does not illuminate.

• If the test lamp does illuminate

1. Disconnect the harness connector at the liquid propane control module.

2. Test for infinite resistance between the signal circuit terminal D and ground.

• If less than infinite resistance, repair the short to ground in the circuit.

• If infinite resistance, test or replace the liquid propane control module.

• If the test lamp does not illuminate

9. Ignition ON.

10. Verify the test lamp illuminates.

• If the test lamp does not illuminate

1. Disconnect the harness connector at the liquid propane control module.

2. Test for 2 ohms or less in the signal circuit end to end.

• If 2 ohms or less, test or replace the liquid propane control module.

• If greater than 2 ohms, repair the open or high resistance in the circuit.

• If the test lamp illuminates

11. Ignition OFF, install the primary fuel pump relay.

12. Disconnect the in-line harness connector at the liquid propane delivery module.

13. Connect a test lamp on the harness side of the in-line between the supply circuit terminal 1 and ground.

14. Verify the test lamp does not illuminates.

• If the test lamp illuminates

1. Disconnect the primary fuel pump relay.

2. Test for less than 1 V on the supply circuit.

• If greater than 1 V, repair the short to voltage on the circuit.

• If less than 1 V, test or replace the primary fuel pump relay.

• If the test lamp does not illuminate

Note: The liquid propane control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the liquid propane control module will turn the fuel pump ON and open both the purge valve and fuel cut off valve for the first 5-8 seconds. After 5-8 seconds the purge valve closes while the cut off valve and fuel pump run for 30 seconds total.

15. Ignition ON.

16. Verify the test lamp illuminates.

• If the test lamp does not illuminate

1. Disconnect the primary fuel pump relay.

2. Test for less than 2 ohms on the supply circuit end to end.

• If 2 ohms or greater , repair the open or high resistance on the circuit.

• If less than 2 ohms, test or replace the primary fuel pump relay.

• If the test lamp illuminates

17. Test or replace the liquid propane delivery module.

LPG Fuel Cut-Off Solenoid Valve - Front Test

1. Remove the LPG cut-off solenoid valve - front relay.

2. Connect a test lamp between the voltage supply circuit terminal E and ground.

3. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Repair the open or high resistance in the circuit.

• If the test lamp illuminates

4. Connect a test lamp between the voltage supply circuit terminal F and ground.

5. Verify the test lamp illuminates.

• If the test lamp does not illuminate
Repair the open or high resistance in the circuit

• If the test lamp illuminates

6. Connect a test lamp between the voltage supply circuit terminal E and the signal circuit terminal D.

7. Ignition OFF.

8. Verify the test lamp does not illuminate.

• If the test lamp illuminates

1. Disconnect the harness connector at the liquid propane control module.

2. Test for infinite resistance between the signal circuit terminal D and ground.

• If less than infinite resistance, repair the short to ground in the circuit.

• If infinite resistance replace the liquid propane control module.

• If the test lamp does not illuminate

Note: The liquid propane control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the liquid propane control module will turn the fuel pump ON and open both the purge valve and fuel cut off valve for the first 5-8 seconds. After 5-8 seconds the purge valve closes while the cut off valve and fuel pump run for 30 seconds total.

9. Ignition ON.

10. Verify the test lamp illuminates.

• If the test lamp does not illuminate

1. Disconnect the harness connector at the liquid propane control module.

2. Test for 2 ohms or less in the signal circuit end to end.

• If 2 ohms or less, test or replace the liquid propane control module.

• If greater than 2 ohms, repair the open or high resistance in the circuit.

• If the test lamp illuminates

11. Ignition OFF, install the LPG cut-off solenoid valve - front relay.

12. Disconnect the in-line harness connector at the liquid propane delivery module.

13. Connect a test lamp on the harness side of the in-line between the supply circuit terminal 1 and ground.

14. Verify the test lamp does not illuminate.

• If the test lamp illuminates

1. Disconnect the LPG cut-off solenoid valve - front relay.

2. Test for less than 1 V on the supply circuit.

• If greater than 1 V, repair the short to voltage on the circuit.

• If less than 1 V, test or replace the LPG cut-off solenoid valve - front relay.

• If the test lamp does not illuminate

15. Ignition ON

16. Verify the test lamp illuminates.

• If the test lamp does not illuminate

1. Disconnect the LPG cut-off solenoid valve - front relay.

2. Test for less than 2 ohms on the supply circuit end to end.

• If 2 ohms or greater , repair the open or high resistance on the circuit.

• If less than 2 ohms, test or replace the LPG cut-off solenoid valve - front relay.

• If the test lamp illuminates

17. Test or replace the liquid propane delivery module.

LPG Cut-Off Solenoid Valve - Purge Test

1. Disconnect the in-line harness connector at the liquid propane delivery module.

2. Connect a test lamp on the harness side of the in-line between the LPG cut-off solenoid valve - purge control circuit terminal 3 and ground.

3. Ignition OFF.

4. Verify the test lamp does not illuminates.

• If the test lamp illuminates

1. Disconnect the liquid propane control module.

2. Test for less than 1 V on the control circuit.

• If greater than 1 V, repair the short to voltage on the circuit.

• If less than 1 V, test or replace the liquid propane control module.

• If the test lamp does not illuminate

Note: The liquid propane control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the liquid propane control module will turn the fuel pump ON and open both the purge valve and fuel cut off valve for the first 5-8 seconds. After 5-8 seconds the purge valve closes while the cut off valve and fuel pump run for 30 seconds total.

5. Ignition ON.

6. Verify the test lamp illuminates for 5-8 s and then turns OFF.

• If the test lamp does not illuminate

1. Disconnect the liquid propane control module.

2. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground in the circuit.

• If infinite resistance.

3. Test for less than 2 ohms on the control circuit end to end.

• If 2 ohms or greater , repair the open or high resistance on the circuit.

• If less than 2 ohms, test or replace the liquid propane control module.

• If the test lamp remains illuminated
Test or replace the liquid propane control module.

• If the test lamp illuminates of 5-8 s and turns OFF.

7. Test or replace the liquid propane delivery module

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* LPG Control Module Replacement

* LPG Delivery Module Replacement

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