Silverado Classic 2500 4WD V8-6.6L DSL Turbo (2007)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
FUEL SYSTEM DIAGNOSIS
DIAGNOSTIC INSTRUCTIONS
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Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic System Check - Vehicle
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Review Strategy Based Diagnosis for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions provides an overview of each diagnostic category.
CIRCUIT/SYSTEM DESCRIPTION
Fuel is drawn by the fuel injection pump through a pre-filter screen in the tank and to the engine through the fuel supply lines. Fuel flows to the fuel
filter/heater element housing, which combines a water separator, a hand prime pump, fuel heater element and a filter element. The fuel is then
delivered to the high-pressure pump. The integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel
system. The mechanical fuel injection pump at the front of the engine valley includes the fuel supply pump and the high-pressure pump.
HIGH PRESSURE SYSTEM
The much larger section of the pump assembly is the high-pressure fuel injection pump. The pump is engine-driven by the camshaft gear. From the
high-pressure pump, the pressurized fuel flows to the left fuel rail. A balance pipe from the center of the left rail then feeds the right fuel rail. Each fuel
rail supplies one bank of 4 fuel injectors. The fuel rail pressure sensor is mounted in the middle of the right fuel rail.
RETURN SYSTEM
Fuel is used to cool and lubricate the fuel injectors and fuel injection pump. The Fuel Return System is designed to return this fuel to the fuel tank. If
the high side fuel pressure becomes excessive, the Fuel Rail Pressure relief valve releases the fuel into the fuel return system. The return fuel travels
through the fuel cooler and then to the fuel tank.
DIAGNOSTIC AIDS
A Cranks But Will Not Run or Hard Start symptom may exist if air is being drawn into the fuel injection system due to the following conditions:
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Deformed or cut O-rings at the fuel supply line connections
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Improperly seated fuel supply line fittings
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Porous or weathered rubber fuel supply lines
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Fuel filter vent screw not tighten or cross threaded
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Fuel filter not tighten properly
CIRCUIT/SYSTEM VERIFICATION
Observe the Actual Fuel Rail Pressure parameter with a scan tool. During engine cranking, the pressure should be at least 10 MPa. With the engine
running at idle the pressure should be close to the Desired Fuel Rail Pressure. As the engine RPM's increase, the Desired Fuel Rail Pressure and the
Actual Fuel Rail Pressure should closely match each other.
CIRCUIT/SYSTEM TESTING
IMPORTANT: Ensure that a sufficient amount of fuel is in the fuel tank to run the vehicle.
1. Install the CH-48027 to the fuel system service port on the right front side of the engine.
2. Prime the fuel system until 10 psi is indicated on the CH-48027.
3. IMPORTANT: It may be necessary to remove engine components for the visual inspections.
Visually inspect the following items for restrictions or leaks:
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Hoses and lines that are flattening when the engine is running, or have kinks that would restrict the flow of fuel
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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.
6. Disconnect the fuel return pipe and install a J 23738-A.
7. 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.
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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.
8. IMPORTANT: The engine may start, and then stall after briefly running.
Connect the fuel return pipe and crank the engine 2-3 times in 15-second intervals while observing the CH-48027. More than 5 inches Hg
vacuum should be observed during cranking.
