RAM 1500 Truck 2WD V6-3.9L VIN X (1999)
The fuel pump module on all gas powered engines is installed in the top of the fuel tank. The fuel pump module contains the following:
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A combination fuel filter/fuel pressure regulator
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Electric fuel pump
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Fuel pump reservoir
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A separate in-tank fuel filter (at bottom of module)
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Rollover valve (certain modules)
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Fuel gauge sending unit (fuel level sensor)
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Fuel supply line connection at filter/regulator
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A threaded locknut retaining pump module to fuel tank
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A gasket between tank flange and module
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Auxiliary non-pressurized fuel supply fitting (not all engines)
The fuel gauge sending unit (fuel level sensor), and pick-up filter (at bottom of module) may be serviced separately. If the electrical fuel pump
requires service, the entire fuel pump module must be replaced. The fuel filter/fuel pressure regulator may be serviced separately. Refer to Fuel
Filter/Fuel Pressure Regulator Removal/Installation for additional information.
FUEL GAUGE SENDING UNIT
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
variable resistor (track). The resistor track is used to send electrical signals to the Powertrain Control Module (PCM) for fuel gauge operation and
for OBD II emission requirements.
For fuel gauge operation: As fuel level increases, the float and arm move up. This decreases the sending unit resistance, causing the fuel gauge to
read full. As fuel level decreases, the float and arm move down. This increases the sending unit resistance causing the fuel gauge to read empty.
After this fuel level signal is sent to the PCM, the PCM will transmit the data across the CCD bus circuits to the instrument panel. Here it is
translated into the appropriate fuel gauge level reading.
For OBD II emission monitor requirements: A voltage signal is sent from the resistor track on the sending unit to the PCM 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 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 activated if the fuel level in the tank is more than approximately 85 percent of its rated capacity.
