GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H3 🢒 Engine 🢒 Engine Electrical 🢒 Fuel System Diagnosis

System Description

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, 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.

An electric turbine style fuel pump attaches to the fuel sender assembly 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 pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly 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.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

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.
   • Before proceeding with this test, review the User Manual CH 48027-5 for Safety Information and Instructions.

  1. Turn OFF the ignition.
  2. Turn OFF all accessories.
  3. Install a CH-48027 Digital 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?

345-427 kPa (50-62 psi)

Go to Step 4

Go to Step 8

4

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 12

Go to Step 6

6

Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 .

Does the fuel pressure drop off during acceleration, cruise, or hard cornering?

--

Go to Step 9

Go to Symptoms - Engine Controls

7
  1. Turn OFF the ignition.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel feed hose from the fuel rail pipe. Refer to Metal Collar Quick Connect Fitting Service .
  4. Install the J 37287 Fuel Line Shut-off Adapter between the fuel hose and the fuel rail pipe.
  5. Open the valve on the fuel pipe shut-off adapter.
  6. Turn ON the ignition, with the engine OFF.
  7. Command the fuel pump relay ON 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 12

Go to Step 11

8

Is the fuel pressure more than the specified value?

427 kPa (62 psi)

Go to Step 12

Go to Step 9

9

Inspect the fuel feed pipe for a restriction.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

10

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 to Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11
  1. Turn OFF the ignition.
  2. Raise the fuel rail with the fuel pipe connected. Refer to Fuel Injection Fuel Rail Assembly Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump relay ON with a scan tool.
  5. Locate and replace the leaking fuel injector. Refer to Fuel Injector Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the fuel tank module. Refer to Fuel Tank Module Replacement .

Did you complete the replacement?

--

Go to Step 13

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13

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 3