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Fuel System Diagnosis

Fuel System Diagnosis

Diagnostic Instructions


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

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

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


Circuit/System Description

The engine control module (ECM) supplies voltage to the fuel pump flow control module when the ECM detects that the ignition is ON. The voltage signal from the ECM to the fuel pump flow control module remains active for 2 s, unless the engine is in Crank or Run. While this voltage is being received, the fuel pump flow control module closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank fuel pump module in order to maintain the desired fuel rail 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 high pressure fuel through the fuel filter, contained in the fuel tank module, and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. 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 and the fuel rail in order to prevent long cranking times.

Reference Information

Description and Operation

Fuel System Description

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Special Tools


• CH48027 Digital Pressure Gauge

• J 37287 Fuel Line Shut-Off Adapter


For equivalent regional tools, refer to Special Tools .

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 an adequate amount of fuel is in the fuel tank before proceeding.

• The Fuel Pump Enable 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 Instruction.



1. Ignition OFF, all accessories OFF, install a CH 48027 Digital Pressure Gauge. Refer to Fuel Pressure Gauge Installation and Removal .

2.
Note

High fuel pressure readings may result due to hot soak fuel boiling. With the engine OFF, the fuel pressure may increase to the setting of the pressure relief regulator valve, approximately 580 kPa (84 psi).


Ignition ON, engine OFF, command the Fuel Pump Enable ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and does not decrease greater than 34 kPa (5 psi) in 1 minute.

3. Engine ON with the engine idling at normal operating temperature, the Fuel Rail Pressure Sensor parameter should read between 296.4 - 310.3 kPa (43 - 45 psi).


Circuit/System Testing


1.
Note
• The Fuel Pump Enable may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

• DO NOT start the engine.

• High fuel pressure readings may result due to hot soak fuel boiling. With the engine OFF, the fuel pressure may increase to the setting of the pressure relief regulator valve, approximately 580 kPa (84 psi).


Ignition ON, engine OFF, command the Fuel Pump Enable 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).

2. 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 fuel pump module.

• Restricted fuel feed pipe

• Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.

3. Verify the fuel pressure does not decrease greater than 34 kPa (5 PSI) in 1 min.

4. If the fuel pressure decreases more than the specified value, perform the following procedure:

4.1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief .

4.2. Disconnect the chassis fuel feed hose from the engine compartment fuel pipe.

4.3. Install the J 37287 Fuel Line Shut-Off Adapter between the chassis fuel hose and the engine compartment fuel pipe.

4.4. Open the valve on the J 37287 Fuel Line Shut-Off Adapter.

4.5. Ignition ON, command the Fuel Pump Enable ON with a scan tool and bleed the air from the CH 48027 Digital Pressure Gauge.

4.6. Command the Fuel Pump Enable ON with a scan tool.

4.7. Close the valve on the EN 37287 Fuel Line Shut-Off Adapter.

4.8. Monitor the fuel pressure for 1 minute.

4.9. If the fuel pressure decreases greater than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injector(s).

4.10. If the fuel pressure does not decrease greater than 34 kPa (5 psi) within the specified time, replace the fuel tank fuel pump module.

5. 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.

6. If the fuel pressure decreases greater than the specified value, replace the fuel tank fuel pump module.

7. 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.

8. If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank fuel pump module.

• Restricted fuel feed pipe

• Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.

9. If the fuel system tests normal, refer to Symptoms - Engine Controls .


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Fuel Feed Pipe Replacement

• Fuel Injector Replacement

• Fuel Tank Fuel Pump Module Replacement