Fuel System Diagnosis. GMC Truck GMC C Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2005 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Electrical 🢒 Fuel System Diagnosis

System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

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.

The fuel tank stores the fuel supply. 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 pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. 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

Schematic Reference: Fuel Hose/Pipes Routing Diagram

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

Important: Inspect the fuel system for external leaks before proceeding with this diagnostic.

Turn ON the ignition, with the engine OFF.
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

Important: Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.

Turn OFF the ignition.
Turn OFF all accessories.

Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
Turn ON the ignition, with the engine OFF.

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.

Command the fuel pump relay ON with a scan tool.
Observe the fuel pressure gage with the fuel pump commanded ON.

Is the fuel pressure within the specified range?

379-427 kPa (55-62 psi)

Go to Step 4

Go to Step 8

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.

Monitor the fuel pressure gage for one minute.

Does the fuel pressure decrease by more than the specified value?

34 kPa (5 psi)

Go to Step 7

Go to Step 5

Relieve the fuel pressure to the first specified value.
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

Operate the vehicle within the conditions to reproduce the original symptoms.
Monitor the O2 and the Fuel Trim parameters with a scan tool.

Does the scan tool parameters indicate a lean condition?

Go to Step 9

Go to Symptoms - Engine Controls

Turn OFF the ignition.
Relieve the fuel pressure. Refer to Fuel Pressure Relief.
Disconnect the chassis fuel hose from the engine compartment fuel pipe. Refer to Metal Collar Quick Connect Fitting Service or Plastic Collar Quick Connect Fitting Service.
Install the J 37287 Fuel Line Shut-off Adapter between the chassis fuel hose and the engine compartment fuel pipe.
Open the valve on the fuel pipe shut-off adapter.
Turn ON the ignition, with the engine OFF.
Command the fuel pump relay ON with a scan tool.
Bleed the air from the fuel pressure gage.
Command the fuel pump relay ON and then OFF with a scan tool.
Close the fuel feed pipe shut-off valve.
Monitor the fuel pressure gage for one minute.

Does the fuel pressure remain constant?

Go to Step 12

Go to Step 11

Is the fuel pressure more than the specified value?

427 kPa (62 psi)

Go to Step 12

Go to Step 9

Inspect the fuel feed pipe for a restriction.

Did you find and correct the condition?

Go to Step 13

Go to Step 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 Connector Repairs.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

Turn OFF the ignition.
Remove the upper intake manifold. Refer to Upper Intake Manifold Replacement.
Remove the fuel injectors from the intake manifold in order to isolate the leaking fuel injector. Refer to Fuel Injector Replacement.
Turn ON the ignition, with the engine OFF.
Command the fuel pump relay ON with a scan tool.
Replace any leaking fuel injectors. Refer to Fuel Injector Replacement .

Did you complete the replacement?

Go to Step 13

Replace the fuel sender. Refer to Fuel Sender Assembly Replacement.

Did you complete the replacement?

Go to Step 13

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 3