Montana SV6 V6-3.9L (2007)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
Fuel System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic Starting Point - Vehicle
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/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, contained in the fuel sender assembly, 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.
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.
1. Turn ON the ignition, with the engine OFF.
2. Command the fuel pump relay ON with a scan tool.
‹› If the fuel pump does not operate, Refer to Fuel Pump Electrical Circuit Diagnosis. See: Powertrain Management/Computers and Control
Systems/Testing and Inspection/Component Tests and General Diagnostics
3. Turn OFF the ignition.
4. Turn OFF all accessories.
5. Install a J 34730-1A.
6. 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.
7. Observe the J 34730-1A with the fuel pump commanded ON. The fuel pressure should be 345-414 kPa (50-60 psi).
‹› If the fuel pressure is less than 345 kPa (50 psi), inspect for a restricted fuel feed pipe, poor connections at the harness connectors and ground
circuits of the fuel pump, or a faulty fuel sender assembly.
‹› If the fuel pressure is more than 414 kPa (60 psi), replace the fuel sender assembly.
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.
8. Monitor the J 34730-1A for 1 minute. The fuel pressure should not decrease more than 34 kPa (5 psi).
