Fuel System Diagnosis
Fuel System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provide an overview of each diagnostic category.
Circuit/System Description
The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.
The fuel system is a semi-returnless design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A semi-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. The fuel pump is an electric pump that is attached to the primary fuel tank module assembly. The fuel pump also supplies fuel to the siphon jet pump, also attached to the primary fuel tank module. The siphon jet pump draws fuel from the secondary side of the fuel tank to the primary side of the fuel tank. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. A fuel pressure regulator which is also located in the fuel tank, is attached to the primary fuel tank module. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned from the fuel filter to the fuel tank by a separate fuel return pipe.
Special Tools Required
* CH-48027 Digital Fuel Pressure Gage
* J 37287 Fuel Line Shut-off Adapter
Circuit/System Verification
1. Turn OFF the ignition.
2. Relieve the fuel pressure. Refer to Fuel Pressure Relief (With CH 48027) Fuel Pressure Relief (Without CH 48027). Fuel Pressure Relief (With CH 48027) Fuel Pressure Relief (Without CH 48027)
3. Disconnect the chassis fuel hose from the fuel rail.
4. Install the J 37287 between the chassis fuel hose and the fuel rail.
5. Open the valve on the J 37287.
6. Turn ON the ignition, with the engine OFF.
7. Command the fuel pump relay ON with a scan tool.
8. Bleed the air from the CH-48027.
9. Command the fuel pump relay ON and then OFF with a scan tool.
10. Close the fuel feed pipe shut-off valve.
11. Monitor the CH-48027 for one minute.
• If the fuel pressure remains constant, replace the fuel sender assembly.
• If the fuel pressure does not remain constant, locate and replace the leaking fuel injectors.
Circuit/System Testing
Important:
* Inspect the fuel system for damage or external leaks before proceeding.
* Verify that adequate fuel is in the fuel tank before proceeding.
1. Turn ON the ignition, with the engine OFF.
2. Command the fuel pump relay ON with a scan tool.
• If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis. Component Tests and General Diagnostics
3. Turn OFF the ignition.
4. Turn OFF all accessories.
5. Install a CH-48027.
6. Turn ON the ignition, with the engine OFF.
Important:
* The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
* DO NOT start the engine.
Command the fuel pump relay ON with a scan tool.
7. Observe the CH-48027 with the fuel pump commanded ON. The fuel pressure should be 380-410 kPa (55-60 psi).
• If the fuel pressure is less than 380 kPa (55 psi), inspect for a restricted fuel feed pipe, poor connections at the harness connectors and ground circuits of the fuel pump, or a faulty fuel sender assembly.
• If the fuel pressure is more than 410 kPa (60 psi), replace the fuel sender assembly.
Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.
8. Monitor the CH-48027 for 1 minute. The fuel pressure should not decrease more than 34 kPa (5 psi).
• If the fuel pressure decreases more than 34 kPa (5 psi), refer to Circuit/System Testing.
9. Relieve the fuel pressure to 69 kPa (10 psi).
10. Monitor the CH-48027 for 5 minutes. The fuel pressure should not decrease more than 14 kPa (2 psi).
• If the fuel pressure decreases more than 14 kPa (2 psi), replace the fuel sender assembly.
11. Remove the CH-48027.
12. Operate the vehicle within the conditions to reproduce the original symptoms.
13. Monitor the O2 and the Fuel Trim parameters with a scan tool.
• If the scan tool parameters indicate a lean condition, inspect for a restricted fuel feed pipe, poor connections at the harness connectors and ground circuits of the fuel pump, or a faulty fuel sender assembly.
• If the scan tool parameters do not indicate a lean condition, go to Symptoms - Computers and Control System. - Symptoms - Engine Controls
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Fuel Injector and Fuel Rail Replacement
* Fuel Tank Fuel Pump Module Replacement - Left Side