Fuel System Diagnosis RPO NT7

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 tank stores the fuel supply. The electric fuel pump supplies fuel through an in-line fuel filter to the fuel injection system. The pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator, located in the fuel tank, maintains the correct fuel pressure to the fuel injection system. A separate pipe returns unused fuel to the fuel tank.

Description and Operation

Fuel System Description

Electrical Information Reference

Scan Tool Reference

Special Tools Required

Important: 

1. Ignition ON, engine OFF, 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, all accessories OFF, install a CH-48027 . Refer to Fuel Pressure Gage Installation and Removal .
3. Ignition ON, engine OFF, command the fuel pump relay 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 minute.

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.

1. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 345-414 kPa (50-60 psi).

⇒	If the fuel pressure is greater than the specified range, test for a restriction in the return side of the fuel filter. If the fuel filter tests normal, replace the fuel pump 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 pump module.

•	Restricted fuel feed pipe

•	Restricted or plugged fuel filter

•	Restricted or plugged strainer

•	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 minute.

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

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

2.2.	Disconnect the chassis fuel feed hose from the engine compartment fuel pipe. Refer to Metal Collar Quick Connect Fitting Service .

2.3.	Install the J 37287 between the chassis fuel hose and the engine compartment fuel pipe.

2.4.	Open the valve on the J 37287 .

2.5.	Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the CH-48027 .

2.6.	Command the fuel pump relay ON with a scan tool.

2.7.	Close the valve on the J 37287 .

2.8.	Monitor the fuel pressure for 1 minute.

⇒	If the fuel pressure decreases more than 55 kPa (8 psi) within the specified time, locate and replace the leaking fuel injectors.

⇒	If the fuel pressure does not decrease more than 55 kPa (8 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 minutes.

⇒	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 . 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 pump module.

•	Restricted fuel feed pipe

•	Restricted or plugged fuel filter

•	Restricted or plugged strainer

•	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 .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel System Diagnosis RPO NU6

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 tank stores the fuel supply. The electric fuel pump supplies fuel through a fuel filter located in the fuel pump module to the fuel injection system. The pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator, located in the fuel tank, maintains the correct fuel pressure to the fuel injection system.

Description and Operation

Fuel System Description

Electrical Information Reference

Scan Tool Reference

Special Tools Required

Important: 

1. Ignition ON, engine OFF, 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, all accessories OFF, install a CH-48027 . Refer to Fuel Pressure Gage Installation and Removal .
3. Ignition ON, engine OFF, command the fuel pump relay 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 minute.

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.

1. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 345-414 kPa (50-60 psi).

⇒	If the fuel pressure is greater than the specified range, replace the fuel pump fuel reservoir pump fuel strainer orifice.

⇒	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 and the fuel pump fuel reservoir pump fuel strainer orifice.

•	Restricted fuel feed pipe

•	Restricted or plugged fuel filter

•	Restricted or plugged strainer

•	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 minute.

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

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

2.2.	Disconnect the chassis fuel feed hose from the engine compartment fuel pipe. Refer to Metal Collar Quick Connect Fitting Service .

2.3.	Install the J 37287 between the chassis fuel hose and the engine compartment fuel pipe.

2.4.	Open the valve on the J 37287 .

2.5.	Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the CH-48027 .

2.6.	Command the fuel pump relay ON with a scan tool.

2.7.	Close the valve on the J 37287 .

2.8.	Monitor the fuel pressure for 1 minute.

⇒	If the fuel pressure decreases more than 55 kPa (8 psi) within the specified time, replace the fuel pump and the fuel pump fuel reservoir pump fuel strainer orifice.

⇒	If the fuel pressure does not decrease more than 55 kPa (8 psi) within the specified time, locate and replace the leaking fuel injector(s).

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 minutes.

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

4. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 . 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 pump and the fuel pump fuel reservoir pump fuel strainer orifice.

•	Restricted fuel feed pipe

•	Restricted or plugged fuel filter

•	Restricted or plugged strainer

•	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 .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.