Fuel System Diagnosis LTD without Turbocharger

The engine control module (ECM) enables the fuel pump relay when the ignition switch is turned ON. The ECM will disable the fuel pump relay within 2 seconds unless the ECM detects ignition reference pulses. The ECM continues to enable the fuel pump relay as long as ignition reference pulses are detected. The ECM disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

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

Note: 

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 Gage .
3. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 380-420 kPa (55-61 psi) and does not decrease more than 34 kPa (5 psi) in 1 minute.

Note: 

•	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 380-420 kPa (55-61 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

•	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.

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

2.3.	Open the valve on the J 37287 Adapter .

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

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

2.6.	Close the valve on the J 37287 Adapter .

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 Gage . 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

•	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 LDK with Turbocharger

The engine control module (ECM) supplies a high voltage signal to the fuel pump control module (FPCM) when the ECM detects that the ignition is ON. The high voltage signal from the ECM to the FPCM remains active for 2 seconds, unless the engine is in Crank or Run. While this signal 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 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 pump module inside the fuel tank. The fuel pump supplies fuel through the fuel filter and 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 pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pump 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.

Description and Operation

Fuel System Description

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Special Tools

Note: 

1. Ignition OFF, all accessories OFF, install a CH-48027 .
2. Ignition ON, engine OFF, command the fuel pump ON with a scan tool. Verify the fuel pressure is between 395-464 kPa (57-67 psi) and does not decrease greater than 34 kPa (5 psi) in 1 minute.

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 gage while the fuel pump is operating. Verify the fuel pressure is between 395-464 kPa (57-67 psi).

⇒	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 or plugged fuel filter

•	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 greater than 34 kPa (5 psi) in 1 minute.

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

2.1.	Ignition OFF, relieve the fuel pressure.

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

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 ON with a scan tool and bleed the air from the CH-48027 .

2.6.	Command the fuel pump 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 does not decrease greater 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 greater than 14 kPa (2 psi) in 5 minutes.

⇒	If the fuel pressure decreases greater 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 or plugged fuel filter

•	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.