XL-7 2WD V6-3.6L (2007)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
Fuel System Diagnosis
Diagnostic Instructions
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Perform the Diagnostic System Check See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System Check - Vehicle
Diagnostic Information Vehicle Diagnostic Information prior to using this diagnostic procedure.
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Review Strategy Based Diagnosis for an overview of the diagnostic approach. See: Testing and Inspection/Initial Inspection and Diagnostic
Overview/Strategy Based Diagnosis
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Diagnostic Procedure Instructions - Vehicle Diagnostic Information 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 primary fuel tank module, 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.
An electric turbine style fuel pump attaches to the primary fuel tank module inside the fuel tank. The fuel pump supplies high pressure fuel through the
fuel filter, past the fuel pressure regulator, and through the fuel feed pipe to the fuel injection system. The fuel pressure regulator has a T-joint that
diverts the needed fuel to the fuel rail with the unused fuel dropping back into the reservoir of the primary fuel tank module. The primary fuel tank
module 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. The primary fuel tank module also contains a primary jet pump and a secondary jet pump. Fuel pump flow loss,
caused by vapor expulsion in the pump inlet chamber, is diverted to the primary jet pump and the secondary jet pump through a restrictive orifice located
on the pump cover. The primary jet pump fills the reservoir of the primary fuel tank module. The secondary jet pump creates a venturi action which
causes the fuel to be drawn from the secondary side of the fuel tank, through the fuel transfer pipe, to the primary side of the fuel tank.
Diagnostic Aids
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A vehicle that runs out of fuel above empty may indicate a condition with the siphon jet pump, or transfer lines between the fuel tanks. Inspect for
blockage, foreign objects or restrictions in all related hardware.
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A vehicle that runs out of fuel above empty may be caused by an inaccurate fuel level sender. Inspect the float arm for binding, or obstructions.
Special Tools Required
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J 34730-1A Fuel Pressure Gage
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J 37287 Fuel Line Shut-Off Adapters
Circuit/System Verification
NOTE:
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Inspect the fuel system for damage or external leaks before proceeding.
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Verify that adequate fuel is in the fuel tank before proceeding.
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The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
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DO NOT start the engine.
1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF for 3-5 seconds.
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If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis.
2. Ignition OFF, all accessories OFF, install the J 37287 and J 34730-1A. Refer to Fuel Pressure Gage Installation and Removal.
3. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 380-410 kPa (55-60 psi) and remains steady
for 5 minutes.
4. Operate the vehicle within the conditions of the customers concern while monitoring fuel related parameters with a scan tool.
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If the scan tool parameters do not indicate a lean condition, refer to Symptoms - Engine Controls.
Circuit/System Testing
1. Ignition ON, command the fuel pump relay ON with a scan tool and observe the fuel pressure while the fuel pump is operating. Verify the fuel
pressure is between 380-410 kPa (55-60 psi).
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If the fuel pressure is more than the specified range, replace the fuel pump.
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If the fuel pressure is less than the specified range, remove the fuel tank and test/inspect for the following:
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Restricted fuel feed pipe
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Restricted or plugged fuel filter
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Restricted or plugged strainer
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Stuck or binding fuel level float
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Restricted siphon jet pump
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Restricted transfer lines between fuel tanks
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Faulty fuel pressure regulator
