GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 Engine 🢒 Engine Controls - 2.5L (LBK) 🢒 Fuel System Diagnosis

System Description

When the ignition is turned ON, the engine control module (ECM) turns ON 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 ignition reference pulses. If there are no reference pulses, the ECM turns the in-tank fuel pump OFF 2 seconds after the ignition 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 design and is located inside the fuel tank. The fuel pump supplies fuel through a fuel filter, through the fuel feed pipes, and 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.

Diagnostic Aids
    • A hard start or long crank time when the engine is cold can be caused by low fuel pump volume.
    • The fuel pressure should build quickly when the fuel pump is turned ON.
    • If you must wait more than 2 seconds for the fuel pressure to build, suspect low fuel pump volume.
    • For an intermittent condition, refer to Intermittent Conditions .

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: Inspect the fuel system for damage or external leaks before proceeding with this diagnostic.

  1. Turn ON the ignition, with the engine OFF.
  2. Command the fuel pump relay ON with a scan tool.

Does the fuel pump operate?

--

Go to Step 3

Go to Fuel Pump Electrical Circuit Diagnosis

3

Important: Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.

  1. Turn OFF the ignition.
  2. Turn OFF all accessories.
  3. Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  4. Turn ON the ignition, with the engine OFF.

    5. 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.

  5. Command the fuel pump relay ON with a scan tool.
  6. Observe the fuel pressure gage with the fuel pump commanded ON.

Is the fuel pressure within the specified range?

290-331 kPa (42-48 psi)

Go to Step 4

Go to Step 10

4

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.

Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure decrease by more than the specified value?

34 kPa (5 psi)

Go to Step 7

Go to Step 5

5
  1. Relieve the fuel pressure to the first specified value.
  2. Monitor the fuel pressure gage for 5 minutes.

Does the fuel pressure decrease by more than the second specified value?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 20

Go to Step 6

6
  1. Operate the vehicle within the conditions to reproduce the original symptoms.
  2. Monitor the O2S/HO2S and the Fuel Trim parameters with a scan tool.

Does the scan tool parameters indicate a lean condition?

--

Go to Step 13

Go to Diagnostic Aids

7
  1. Turn OFF the ignition.
  2. Remove the vacuum hose from the fuel pressure regulator.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump relay ON with a scan tool.
  5. Inspect for a fuel leak from the fuel pressure regulator vacuum port.

Is the fuel pressure regulator leaking fuel?

--

Go to Step 19

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel pressure pipe and the fuel return pipe from the fuel rail.
  4. Install the J 37287 Fuel Line Shut-off Adapters between both fuel pipes and the fuel rail.
  5. Open the valves on the fuel pipe shut-off adapters.
  6. Turn ON the ignition, with the engine OFF.
  7. Command the fuel pump relay ON and then OFF with a scan tool.
  8. Bleed the air from the fuel pressure gage.
  9. Command the fuel pump relay ON and then OFF with a scan tool.
  10. Close the fuel feed pipe shut-off valve.
  11. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 16

Go to Step 9

9
  1. Turn OFF the ignition.
  2. Open the fuel feed pipe shut-off valve.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump relay ON and then OFF with a scan tool.
  5. Close the fuel return pipe shut-off valve.
  6. Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure remain constant?

--

Go to Step 19

Go to Step 17

10

Is the fuel pressure more than the specified value?

331 kPa (48 psi)

Go to Step 11

Go to Step 13

11
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return pipe from the fuel rail
  4. Attach a length of flexible fuel hose to the fuel rail.
  5. Place the open end of the flexible fuel hose into an approved gasoline container.
  6. Turn ON the ignition, with the engine OFF.
  7. Monitor the fuel pressure gage while the fuel pump is operating.

Is the fuel pressure within the specified range?

290-331 kPa (42-48 psi)

Go to Step 18

Go to Step 12

12

Inspect the fuel rail return pipe and the fuel rail outlet passage for a restriction.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

13
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return pipe from the fuel rail.
  4. Install the J 37287 Fuel Line Shut-off Adapter between the fuel return pip and the fuel rail.
  5. Open the valve in the fuel pipe shut-off adapter.
  6. Turn ON the ignition, with the engine OFF.
  7. Bleed the air from the fuel pressure gage.
  8. Monitor the fuel pressure gage.

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

  9. Command the fuel pump relay ON with a scan tool.
  10. Slowly close the valve in the fuel return pipe shut-off adapter, while the fuel pump is operating.

Does the fuel pressure increase to more than the specified value?

345 kPa (50 psi)

Go to Step 19

Go to Step 14

14

Inspect the following components for a restriction:

    • The fuel filter
    • The fuel feed pipe

Did you find and correct the condition?

--

Go to Step 21

Go to Step 15

15

Inspect the harness connectors and the ground circuits of the fuel pump for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

16
  1. Remove the fuel sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Inspect the following items:
    3. • The fuel pump flex hose for damage
    • The in-tank fuel pump harness connectors for poor connections
    • The fuel strainer for a restriction
    • The fuel tank for contaminants

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

17
  1. Open the fuel return pipe shut-off valve.
  2. Turn OFF the ignition.
  3. Raise the fuel rail, with the fuel lines connected. Refer to Fuel Injection Fuel Rail Assembly Replacement .
  4. Turn ON the ignition, with the engine OFF.
  5. Command the fuel pump relay ON with a scan tool.
  6. Locate and replace the leaking fuel injector. Refer to Fuel Injection Fuel Rail Assembly Replacement .

Did you complete the replacement?

--

Go to Step 21

--

18

Repair the restricted fuel return pipe.

Did you complete the repair?

--

Go to Step 21

--

19

Important: Inspect for a missing or damaged O-ring seal before replacing the fuel pressure regulator.

Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .

Did you complete the replacement?

--

Go to Step 21

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20

Replace the fuel pump.

Did you complete the replacement?

--

Go to Step 21

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21

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3