Dodge 2000 DURANGO Service Manual page 723

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DESCRIPTION AND OPERATION (Continued)
Fig. 2 Fuel Pump Module Components (Typical
Pump Module Shown)
1 – FUEL FILTER/PRESSURE REGULATOR
2 – ELECTRICAL CONNECTOR
3 – ELECTRIC FUEL PUMP
4 – FUEL GAUGE FLOAT
5 – FUEL PUMP INLET FILTER
6 – FUEL GAUGE SENDING UNIT
7 – MODULE LOCK TABS (3)
injectors. Fuel pressure that has dropped to 0
psi on a cooled down vehicle (engine off) is a
normal condition. Refer to the Fuel Pressure Leak
Down Test for more information.
FUEL GAUGE SENDING UNIT
DESCRIPTION
The fuel gauge sending unit (fuel level sensor) is
attached to the side of the fuel pump module. The
sending unit consists of a float, an arm, and a vari-
able resistor track (card).
OPERATION
The fuel pump module has 4 different circuits
(wires). Two of these circuits are used for the fuel
gauge sending unit for fuel gauge operation, and for
certain OBD II emission requirements. The other 2
wires are used for electric fuel pump operation.
For Fuel Gauge Operation: A constant current
source of about 32 mA is supplied to the resistor
track on the fuel gauge sending unit. This is fed
directly from the Powertrain Control Module (PCM).
The resistor track is used to vary the voltage depend-
ing on fuel tank float level. As fuel level increases,
the float and arm move up, which decreases voltage.
As fuel level decreases, the float and arm move
down, which increases voltage. The varied voltage
signal is returned back to the PCM through the sen-
sor return circuit. Output voltages will vary from
about.6 volts at FULL, to about 8.6 volts at EMPTY
(Jeep models), or, about 7.0 volts at EMPTY (Dodge
Truck models). NOTE: For diagnostic purposes,
this voltage can only be verified with the fuel
gauge sending unit circuit closed (i.e. having all
of the sending units electrical connectors con-
nected).
Both of the electrical circuits between the fuel
gauge sending unit and the PCM are hard-wired (not
multi-plexed). After the voltage signal is sent from
the resistor track, and back to the PCM, the PCM
will interpret the resistance (voltage) data and send
a message across the multi-plex bus circuits to the
instrument panel cluster. Here it is translated into
the appropriate fuel gauge level reading. Refer to
Instrument Panel for additional information.
For OBD II Emission Monitor Requirements:
The PCM will monitor the voltage output sent from
the resistor track on the sending unit to indicate fuel
level. The purpose of this feature is to prevent the
OBD II system from recording/setting false misfire
and fuel system monitor diagnostic trouble codes.
The feature is activated if the fuel level in the tank
is less than approximately 15 percent of its rated
capacity. If equipped with a Leak Detection Pump
(EVAP system monitor), this feature will also be acti-
vated if the fuel level in the tank is more than
approximately 85 percent of its rated capacity.
FUEL FILTER/FUEL PRESSURE REGULATOR
DESCRIPTION
A combination fuel filter and fuel pressure regula-
tor (Fig. 3) is used on all engines. It is located on the
top of the fuel pump module. A separate frame
mounted fuel filter is not used with any engine.
Both fuel filters (at bottom of fuel pump module
and within fuel pressure regulator) are designed for
extended service. They do not require normal sched-
uled maintenance. Filters should only be replaced if
a diagnostic procedure indicates to do so.
OPERATION
Fuel Pressure Regulator Operation: The pres-
sure regulator is a mechanical device that is not con-
trolled by engine vacuum or the powertrain control
module (PCM).
The regulator is calibrated to maintain fuel system
operating pressure of approximately 339 kPa
kPa (49.2 psi 5 psi) at the fuel injectors. It con-
tains a diaphragm, calibrated springs and a fuel
return valve. The internal fuel filter (Fig. 3) is also
part of the assembly.
FUEL SYSTEM 14 - 3
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