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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> External Pages >> Different car >> Section 514 (Engine Controls/Fuel - Hybrid (LZ1) - DTC P0351 To DTC P3449 And Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> Fuel System Diagnosis >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2012 GMC Yukon, 2012 Chevrolet Tahoe, and 2012 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
    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 Enable ON with a scan tool and observe the fuel pressure gauge while the fuel pump is operating. Verify the fuel pressure is between 345-414 kPa (50-75 psi).
    • 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
    • Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
    2. 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:
    1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief (Without CH 48027) .
    2. Install the J 37287  fuel line shut-off adapters between the fuel feed pipe and the fuel rail.
    3. Open the valve on the J 37287  fuel line shut-off adapters.
    4. Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the fuel pressure gauge.
    5. Close the valve on the J 37287  fuel line shut-off adapters.
    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.
    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. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027  fuel pressure gauge. The fuel pressure should not drop off during accelerations, 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.
  5. If the fuel system components test normal, refer to Symptoms - Engine Controls .
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