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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 12 (Engine Controls - 6.6L - Troubleshooting & Diagnosis) >> Fuel System Diagnosis >> Circuit/System Testing

Circuit/System Testing

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IMPORTANT: Ensure that a sufficient amount of fuel is in the fuel tank to run the vehicle.
  1. Install the J 44638  to the fuel system service port on the right front side of the engine. See Special Tools .
  2. Prime the fuel system until 10 psi is indicated on the J 44638  . See Special Tools .
    3. IMPORTANT: It may be necessary to remove engine components for the visual inspections.
  3. Visually inspect the following items for restrictions or leaks:
    • Hoses and lines that are flattening when the engine is running, or have kinks that would restrict the flow of fuel
    • Fuel leaks between the fuel filter/heater element housing and the fuel injection pump
  4. Repair any leaks or replace any components found to be damaged or leaking.
  5. Disconnect the fuel supply line at the engine and cap off the pipe on the engine with a rubber plug and clamp. Refer to Quick Connect Fitting(s) Service (Metal Collar) .
  6. Remove the ignition 1 relay and crank the engine 2-3 times in 15-second intervals while observing the J 44638  . See Special Tools .
    • If more than 5 inches Hg of vacuum was not observed on the vacuum gage during cranking, replace the fuel injection pump. Refer to Fuel Injection Pump Replacement .
  7. Disconnect the fuel return pipe and install a J 23738-A  .
  8. Apply 25 inches Hg of vacuum to the fuel return pipe and wait for at least one minute for the system to stabilize. Repeat this step 6 additional times.
    • If vacuum drops below 8 inches Hg of vacuum within 10 minutes, repair the air leak at fuel filter/heater element housing connections or at the fuel hoses/pipes, on the engine.
  9. Disconnect and plug the chassis fuel supply line at the fuel tank. Refer to Quick Connect Fitting(s) Service (Metal Collar) .
  10. Apply at least 25 inches Hg of vacuum to the supply hose with the J 23738-A  and wait more than one minute for the system to stabilize. Repeat this action 10 times.
    • If the vacuum drops below 8 inches Hg of vacuum within 10 minutes, repair the air leak in the fuel supply line between the engine and fuel tank.
  11. Except for the fuel supply line, install all components and lines that were previously removed or disconnected.
  12. Install the EN-47969  on the fuel supply line at the engine. See Special Tools . Create a vertical loop in the hose to observe the incoming fuel for air bubbles.
  13. Prime the fuel system 30 times to remove the air from the fuel hoses. Continue to prime the fuel system until the engine starts and runs.
  14. Run the engine for at least 10 minutes to allow the fuel system to stabilize, and purge any air from the system.
  15. Observe the fuel entering the EN-47969  for air bubbles. See Special Tools .
  16. Install the fuel sender, fuel tank, and all fuel system connections and components that were previously disconnected. Leave the EN-47969  connected to the fuel supply line. See Special Tools . Prime the fuel system 30 times to remove the air from the fuel hoses. Continue to prime the fuel system until the engine starts and runs. Observe the fuel entering the transparent hose.
    • If air bubbles are still present, refer to Diagnostic Aids .
    • If no air bubbles are present, remove the EN-47969  and run the engine to ensure no fuel leaks exist. See Special Tools .
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