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Home >> Chevrolet >> 2007 >> Chevy Express G2500, Van Cargo, 6.6 6 >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 8 (Engine Control System & Fuel System - 6.6L (LLY) - Troubleshooting & Diagnosis) >> Fuel System Diagnosis >> Circuit/System Testing

Circuit/System Testing

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  1. Remove the engine cover. Refer to Engine Cover Replacement .
  2. Clean all of the fuel lines between the fuel injection pump and the fuel injectors using brake cleaning solvent, and let dry.
    3. IMPORTANT: It may be necessary to remove engine components for the visual inspections.
  3. Install the CH-48027  to the fuel system service port on the right front side of the engine. See Special Tools .
    4. IMPORTANT: Fuel line connections should be inspected thoroughly for O-ring damage.
  4. Command the fuel pump ON with a scan tool and observe the fuel pressure gage to ensure that fuel pressure is present. Visually inspect the engine and chassis for leaks or damage to the fuel hoses, fuel lines, and fuel system components.
    • Repair any leaks or replace any components found to be damaged or leaking.
    • If the fuel pump did not run and fuel pressure was not observed, refer to Fuel Pump Electrical Circuit Diagnosis .
    • If the fuel pump did run and fuel pressure was not observed, inspect the fuel feed line for a vacuum leak between the DFCM and the fuel tank sender.
  5. If leaks or damage were not found on the fuel system, turn OFF the fuel pump and disconnect the fuel supply line at the engine. Refer to Metal Collar Quick Connect Fitting Service .
  6. Cap off the fuel supply pipe on the engine with a rubber plug and a clamp.
    7. IMPORTANT: The fuel prime pump must be disabled before using the CH-48027  to diagnose the fuel system. See Special Tools . Fuel pressure with the pump running is more than the gage is designed to handle and may cause damage to the gage.
  7. Remove the fuel pump relay. Crank the engine and observe the CH-48027  to see if the fuel injection pump is creating at least 10 inches Hg of vacuum. See Special Tools .
    • If vacuum is present during cranking but bleeds off rapidly, repair the leak in the fuel supply line.
    • If vacuum is not present during cranking, replace the fuel injection pump. Refer to Fuel Injection Pump Replacement .
    8. IMPORTANT: Changes in engine speed can cause an increase of air bubbles that enter the EN-47969  . See Special Tools . An air pocket at the top of the EN-47969  loop is considered a normal condition. See Special Tools .
  8. Remove the rubber plug from the fuel supply line and install the EN-47969  . See Special Tools . Create a vertical loop in the hose to observe the incoming fuel for air bubbles. Command the Fuel Pump ON with a scan tool and prime the fuel system until all air has been purged. Start and run the engine for at least 10 minutes to allow the fuel system to stabilize. At a stabilized idle, observe the fuel entering the EN-47969  for air bubbles. See Special Tools .
  9. 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 . Command the fuel pump ON with a scan tool and prime the fuel system until all air is purged. Start and run the engine, while observing 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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