Envoy 2WD V8-5.3L (2007)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
Fuel System Diagnosis
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit/System Description
When the ignition is turned ON, the engine control module (ECM) supplies power to the in-tank fuel pump, by energizing the fuel pump relay. The
in-tank fuel pump remains ON as long as the engine is cranking or running and the ECM receives crankshaft reference pulses. If there are no reference
pulses, the ECM turns the in-tank fuel pump OFF, 2 seconds after the ignition switch is turned ON or 2 seconds after the engine stops running. The
electric fuel pump is incorporated into the modular fuel pump and sender assembly and is located inside the fuel tank. The fuel pump supplies fuel
through a fuel filter, also located in the modular fuel pump and sender assembly, through the fuel feed pipes, to the fuel rail assembly. The fuel pump
provides fuel at a pressure above the pressure needed by the fuel injectors. The fuel pressure regulator, located in the modular fuel pump and sender
assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the
pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.
Circuit/System Verification
Important:
* Inspect the fuel system for damage or external leaks before proceeding.
* Verify that adequate fuel is in the fuel tank before proceeding.
* The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF.
‹› If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis. See: Computers and Control Systems/Testing and
Inspection/Component Tests and General Diagnostics
* Ignition OFF, all accessories OFF, install the J34730-1A. Refer to Fuel Pressure Gage Installation and Removal.
* Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and remains
steady for 5 minutes.
Circuit/System Testing
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.
Ignition ON, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the
fuel pressure is between 345-414 kPa (50-60 psi).
‹› If the fuel pressure is greater than the specified range, replace the fuel pump.
‹› 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
* Restricted or plugged fuel filter
* Restricted or plugged strainer
* Stuck or binding fuel level float
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
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.
* 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:
