Fuel System Diagnosis w/FPCM

The engine control module (ECM) supplies voltage to the fuel pump control module (FPCM) when the ECM detects that the ignition is ON. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in Crank or Run. While this voltage is being received, the FPCM 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 rail pressure.

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel pump module, eliminating the need for a return pipe from the engine. 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 pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter 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 pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pressure regulator, a part of the fuel pump module, maintains the correct fuel pressure to the fuel injection system. The fuel pump module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

Description and Operation

Fuel System Description

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Special Tools

Important: 

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

Important: 

•	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 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 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

•	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.	Install the J 37287 between the fuel feed pipe and the fuel rail.

2.3.	Open the valve on the J 37287 .

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

2.5.	Command the fuel pump ON and then OFF with a scan tool.

2.6.	Close the valve on the J 37287 .

2.7.	Monitor the fuel pressure for 1 minute.

⇒	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 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

•	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 w/o FPCM

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, also located in the modular fuel pump and sender assembly, 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. The fuel pressure regulator, located in the modular fuel pump and sender assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Special Tools

Important: 

•	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 relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

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 System Diagnosis.

2. Ignition OFF, all accessories OFF, install the CH-48027 . Refer to Fuel Pressure Gage Installation and Removal.
3. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and remains steady for 5 minutes.

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, 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.

⇒	If the fuel pressure is less than the specified range, remove the fuel tank and test, inspect, and repair the items listed below. If all items test normal, replace the fuel pump.

•	Restricted fuel feed pipe

•	Restricted or plugged fuel filter

•	Restricted or plugged strainer

•	Stuck or binding fuel level float

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

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 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.	Install the J 37287 between the fuel feed pipe and the fuel rail.

2.3.	Open the valve on the J 37287 .

2.4.	Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the fuel pressure gage.

2.5.	Close the valve on the J 37287 .

2.6.	Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.

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

2.7.	If the fuel system test normal, replace the fuel pump.

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. Remove the J 37287 and CH-48027 . Refer to Fuel Pressure Gage Installation and Removal.
5. Operate the vehicle within the conditions of the customers concern while monitoring the fuel trim and O2 parameters with a scan tool. The scan tool parameters should not indicate a lean condition.

⇒	If the scan tool parameters indicate a lean condition, test for a restricted fuel feed pipe, restricted fuel filter, or poor connections at the harness connectors and ground circuits of the fuel pump. If all test normal, replace the fuel pump.

6. If the fuel system components test normal, refer to Symptoms - Engine Controls.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.