Fuel System Diagnosis (Without FPCM)
Fuel System Diagnosis (Without FPCM)
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 2 s 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 ECM disables the fuel pump relay within 2 s if ignition reference pulses cease to be detected and the ignition remains ON.
The fuel system is an electronic returnless on-demand design. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pump module contains a reverse flow check valve. The check valve maintains fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
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
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Special Tools
* CH-48027 - Digital Pressure Gauge
* J 37287 - Fuel Line Shut-off Adapter
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 tank before proceeding.
* The fuel pump may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
* Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.
* DO NOT perform the Fuel System Diagnosis if the engine coolant temperature is above 60°C (150°F). High fuel pressure readings may result due to hot soak fuel boiling. With the engine OFF, the fuel pressure may increase beyond the pressure relief valves set point of 550 kPa = / -5 % (80 psi ±5 %).
1. Ignition OFF, all accessories OFF, install a CH-48027 - Digital Pressure Gauge. Refer to Fuel Pressure Gauge Installation and Removal Testing and Inspection.
2. Ignition ON, engine OFF, command the fuel pump ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and does not decrease more than 34 kPa (5 psi) in 1 min.
3. Engine ON with the engine idling at normal operating temperature, the Fuel Rail Pressure Sensor parameter should read between 345-414 kPa (50-60 psi).
Circuit/System Testing
Note:
* The fuel pump may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
* DO NOT start the engine.
1. Ignition ON, engine OFF, command the fuel pump ON with a scan tool and observe the fuel pressure gauge while the fuel pump is operating. Verify the fuel pressure is between 345-414 kPa (50-60 psi).
• If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the fuel pump module.
* Restricted fuel feed pipe
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
2. Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 min.
• If the fuel pressure decreases more than the specified value, perform the following procedure:
1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief (Without CH-48027) Fuel Pressure Relief (Without CH-48027)Fuel Pressure Relief (CH-48027) Fuel Pressure Relief (CH-48027).
2. Install the J 37287 - Fuel Line Shut-off Adapter between the fuel feed pipe and the fuel rail.
3. Open the valve on the J 37287 - Fuel Line Shut-off Adapter.
4. Ignition ON, command the fuel pump ON with a scan tool and bleed the air from the CH-48027 - Digital Pressure Gauge.
5. Command the fuel pump ON and then OFF with a scan tool.
6. Close the valve on the J 37287 - Fuel Line Shut-off Adapter.
7. Monitor the fuel pressure for 1 min.
• If the fuel pressure decreases more than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injectors.
• If the fuel pressure does not decrease more than 34 kPa (5 psi) within the specified time, replace the fuel pump module.
3. Relieve the fuel pressure to 69 kPa (10 psi). Verify that the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 min.
• If the fuel pressure decreases more than the specified value, replace the fuel pump module.
4. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 - Digital Pressure Gauge. The fuel pressure should not drop off during acceleration, cruise or hard cornering.
• If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the primary fuel tank module.
* Restricted fuel feed pipe
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
5. If the fuel system tests normal, refer to Symptoms - Engine Controls (Without LC8) Symptom Related Diagnostic ProceduresSymptoms - Engine Controls (LC8\FHZ) Symptom Related Diagnostic ProceduresSymptoms - Engine Controls (LC8\KO7) Symptom Related Diagnostic Procedures.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Fuel Injector Replacement Removal and ReplacementFuel Injector Replacement (LPG 3 Tank) Removal and Replacement
* Fuel Tank Fuel Pump Module Replacement Service and Repair