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1G-24 Fuel System:
Fuel System Diagnosis
Diagnostic Instructions
• Perform the "Diagnostic System Check - Vehicle
Diagnostic Information: " prior to using this diagnostic
procedure.
• Review "Strategy Based Diagnosis: " for an overview
of the diagnostic approach.
• "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
• 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.
• 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.
Reference Information
Description and Operation
"Fuel System Description"
Electrical Information Reference
• "Circuit Testing: "
• "Connector Repairs: "
• "Testing for Intermittent Conditions and Poor
Connections: "
• "Wiring Repairs: "
Scan Tool Reference
• "Scan Tool Data List - Engine Controls - 3.6L (LY7): "
• "Scan Tool Data Definitions - Engine Controls - 3.6L
(LY7): "
• "Scan Tool Output Controls - Engine Controls - 3.6L
(LY7): "
Special Tools Required
• J 34730-1A Fuel Pressure Gage
• J 37287 Fuel Line Shut-Off Adapters
Circuit/System Verification
NOTE
• 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.
• 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.
➢ 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.
➢ If the scan tool parameters do not indicate a lean
condition, refer to "Symptoms - Engine Controls: ".
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Troubleshooting
