When the ignition is turned ON, the engine control module (ECM) supplies power to the in-tank fuel pump, by energizing the fuel pump relay. The in-tank fuel pump remains ON as long as the engine is cranking or running and the ECM receives crankshaft reference pulses. If there are no reference pulses, the ECM turns the in-tank fuel pump OFF, 2 seconds after the ignition switch is turned ON or 2 seconds after the engine stops running. The electric fuel pump is incorporated into the modular fuel pump and sender assembly and is located inside the fuel tank. The fuel pump supplies fuel through a fuel filter, through the fuel feed pipes, to the fuel rail assembly. The fuel pump provides fuel at a pressure above the pressure needed by the fuel injectors. A fuel pressure regulator, attached to the fuel rail, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate fuel return pipe.

Description and Operation

Fuel System Description

Electrical Information Reference

Scan Tool Reference

Special Tools Required

Important: 

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

•	Verify that adequate fuel is in the fuel tank before proceeding.

1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF.

⇒	If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis .

2. Ignition OFF, install the J 34730-1A . Refer to Fuel Pressure Gage Installation and Removal .

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.

3. Ignition ON, all accessories OFF, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 294-335 kPa (43-49 psi) and remains steady for 5 minutes.
4. Operate the vehicle within the conditions of the customers concern while monitoring fuel related parameters with a scan tool.

⇒	If the scan tool parameters do not indicate a lean condition, refer to Symptoms - Engine Controls .

1. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 294-335 kPa (43-49 psi).

⇒	If less than the specified range, perform one of the following procedures:

Greater than the specified value:

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

1.2.	Disconnect the fuel return pipe from the fuel rail, and attach a length of flexible fuel hose to the fuel rail with the open end of the hose placed into an approved gasoline container.

1.3.	Ignition ON, observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 294-335 kPa (43-49 psi).

⇒	If less than the specified range, locate and repair the restriction in the fuel return line.

⇒	If greater than the specified range, replace the fuel pressure regulator.

Less than the specified value:

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

1.2.	Disconnect the fuel return pipe from the fuel rail, and install the J 37287 between the fuel return pipe and the fuel rail.

1.3.	Open the valve on the J 37287 and bleed the air from the fuel pressure gage.

Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system.

1.4.	Slowly close the valve on the J 37287 while the fuel pump is operating. Observer the fuel pressure gage.

⇒	If greater than the specified range, replace the fuel pressure regulator.

⇒	If less than the specified range, test for a restricted fuel feed pipe or restricted fuel filter. If the system tests OK, replace the fuel pump.

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.

2. Verify the fuel pressure remains constant within 34 kPa (5 psi) for 1 minute.

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

2.1.	Inspect the fuel pressure regulator vacuum hose for fuel.

⇒	If fuel is found in the vacuum hose, replace the fuel pressure regulator.

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

2.3.	Install a J 37287 between the fuel feed pipe and the fuel rail, and between the fuel return pipe and the fuel rail.

2.4.	Open the valves on both of the J 37287 and bleed the air from the fuel pressure gage.

2.5.	Close the valve on the J 37287 that is connected to the fuel feed pipe. Observe the fuel pressure gage for 1 minute.

⇒	If the fuel pressure remains constant, replace the fuel pump.

2.6.	Ignition OFF, open the valve on the J 37287 that is connected to the fuel feed pipe.

2.7.	Ignition ON, close the valve on the J 37287 that is connected to the fuel return pipe. Observe the fuel pressure gage for 1 minute.

⇒	If the fuel pressure remains constant, replace the fuel pressure regulator.

⇒	If the fuel pressure drops, locate and replace the leaking fuel injector.

3. Relieve the fuel pressure to 69 kPa (10 psi). Verify the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 minutes.

⇒	If the fuel pressure decreases more than the specified value, replace the fuel pump.

4. Operate the vehicle within the conditions of the customers concern while observing the scan tool fuel related parameters.

⇒	If the scan tool parameters indicate a lean condition, test/inspect for the following:

•	Restricted fuel feed pipe

•	Restricted fuel filter

•	Faulty fuel pressure regulator

•	Poor connections at the harness connectors and ground circuits of the fuel pump

⇒	If all test normal and the scan tool parameters indicate a lean condition, replace the fuel pump.

Fuel Pressure Regulator

1. Ignition OFF, install the J 34730-1A . Refer to Fuel Pressure Gage Installation and Removal .
2. Disconnect the vacuum hose from the fuel pressure regulator.
3. Engine idling, observe the fuel pressure gage, while connecting the vacuum hose to the fuel pressure regulator. The fuel pressure should decrease.

Fuel Pump

1. Ignition OFF, remove the fuel pump relay.
2. Install a DMM, set to the amperage scale, between terminals 30 and 87 on the underhood fuse block assembly. Observe the DMM. The amperage should be between 6-10 Amps.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.