Component Tests and General Diagnostics
Fuel System Diagnosis
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) supplies voltage to the fuel pump control module when the ECM detects that the ignition is ON. The voltage from the ECM to the fuel pump control module remains active for 2 s, unless the engine is in Crank or Run. While this voltage is being received, the fuel pump control module closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel line pressure.
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 tank module inside the fuel tank. The fuel pump supplies fuel through the fuel feed pipe to the high pressure fuel pump. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel tank module. The function of the venturi pump is to fill the fuel tank module reservoir. The fuel tank module contains a reverse flow check valve. The check valve maintains fuel pressure in the fuel feed pipe in order to prevent long cranking times.
Diagnostic Aids
Observe the Misfire Counters or perform the Fuel Injector Balance Test to help identify a leaking fuel injector.
Reference Information
Description and Operation
Fuel System Description Fuel System Description
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
* EN 37287 - Fuel Line Shut-Off Adapter
Circuit/System Verification
Note:
* Repair all fuel system related DTCs before performing this 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.
1. Ignition OFF, all accessories OFF, install a CH 48027 - Gauge.
Note: 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 regulator valve's setting point of 690 kPa (100 psi) ± 5 percent.
2. Ignition ON, engine OFF, command the fuel pump ON with a scan tool. Verify the fuel pressure is between 345-690 kPa (50-100 psi) with the fuel pump running.
3. Engine idling at normal operating temperature, the Fuel Pump Flow Control Module Fuel Pressure Sensor parameter should read between 300-400 kPa (43-58 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 345-690 kPa (50-100 psi).
• If the fuel pressure is greater than the specified range, replace the fuel tank module.
• 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 tank 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, after the fuel pump is turned off, decreases to 500-599 kPa (72-87 psi), and does not decrease more than 34 kPa (5 psi) in 1 minute from that point.
• If the fuel pressure stays above 600 kPa (87 psi), replace the fuel pump module.
• 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)Fuel Pressure Relief (High Side) Fuel Pressure Relief (High Side).
2. Disconnect the chassis fuel feed hose from the engine compartment fuel pipe.
3. Install the EN 37287 - Shut-Off Adapterbetween the chassis fuel hose and the engine compartment fuel pipe.
4. Open the valve on the EN 37287 - Shut-Off Adapter.
5. Ignition ON, command the fuel pump ON with a scan tool and bleed the air from the CH 48027 - Gauge.
6. Command the fuel pump ON and then OFF with a scan tool.
7. Close the valve on the EN 37287 - Shut-Off Adapter.
8. 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 injector(s).
• If the fuel pressure does not decrease more than 34 kPa (5 psi) within the specified time, replace the fuel tank module.
3. Relieve the fuel pressure to 69 kPa (10 psi). Verify that the fuel pressure does not decrease greater than 14 kPa (2 psi) in 5 min.
• If the fuel pressure decreases greater than the specified value, replace the fuel tank module.
4. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH 48027 - 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 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 Symptoms - Engine Controls , Fuel Injector Solenoid Coil Test Fuel Injector Solenoid Coil Test , and Fuel Injector Balance Test Fuel Injector Balance Test.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Fuel Feed Pipe Replacement (LLT) Fuel Feed Pipe Replacement (LLT)
* Fuel Injector Replacement (LLT) Fuel Injector Replacement (LLT)
* Fuel Line Replacement - Chassis Fuel Line Replacement - Chassis
* Fuel Pump Fuel Feed Hose Replacement Fuel Pump Fuel Feed Hose Replacement
* Fuel Tank Module Replacement Service and Repair