Dodge ram truck 3500 1996 Service Manual page 1305

B R
- — FUEL SYSTEM 1 4 - 7 1
D E S C R I P T I O N A N D O P E R A T I O N
(Continued)
FUEL TANK MODULE
An electric fuel pump is not used i n the fuel tank
module for diesel powered engines. Fuel is supplied
by the fuel transfer pump and the fuel injection
pump.
The fuel tank module is installed in the top of the
fuel tank (Fig. 2). The fuel tank module (Fig. 2) or
(Fig. 3) contains the following components:
• Fuel reservoir
• A separate in-tank fuel filter
• Pressure relief/rollover valve
• Fuel gauge sending unit
• Fuel supply line connection
• Fuel return line connection
• Auxiliary fuel supply fitting
The electric fuel pump, normally mounted in the
fuel pump module on gas powered engines, is not
used with diesel powered engines.
PRESSURE RELIEF/
ROLLOVER VALVE
PLASTIC
LOCKNUT
FRONT
OF TANK
AUX. FUEL
SUPPLY FITTING
FUEL
SUPPLY
UNE
FUEL
RETURN
UNE
FUEL GAUGE
SENDING
UNIT
ELECTRICAL
CONNECTOR
J9414-70
Fig. 2 Top View of Fuel Tank Module—Diesel
FUEL GAUGE LOCKING
FLOAT
v
SENDING UNIT TABS
ELECTRIC
F U E L
PUMP
MOUNTING
S C R E W S
IN-TANK
FUEL FILTER
J 9 4 1 4 - 3 3
Fig. 3 Fuel Gauge Sending Unit—Typical
FUEL GAUGE SENDING UNIT
The fuel gauge sending unit 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
track is used to send an electrical signal used for fuel
gauge operation.
As the fuel level increases, the float and arm move
up. This decreases the sending unit resistance, caus­
ing the fuel gauge on the instrument panel to read
full. As the fuel level decreases, the float and arm
move down. This increases the sending unit resis­
tance, causing the fuel gauge on the instrument
panel to read empty.
FUEL HEATER
The fuel heater is used to prevent diesel fuel from
waxing during cold weather operation. The fuel
heater is located on the left side of the engine above
the starter motor (Fig. 4).
The heater assembly is equipped with a built-in
sensor (thermostat) (Fig. 4) that senses fuel temper­
ature. When the temperature is below 40 degrees F,
the built-in sensor allows current to flow to the
built-in heater element warming the fuel. When the
temperature is above 80 degrees F, the sensor stops
current flow to the heater element.
FUEL TEMPERATURE SENSOR
ELECTRICAL
CONNECTOR
FUEL
HEATER
FUEL
TRANSFER
PUMP
J9414-94
Fig. 4 Fuel Heater and Temperature Sensor Location
Voltage to operate the fuel heater is supplied from
the ignition switch and through the fuel heater relay.
Also refer to Fuel Heater Relay.
The fuel heater and fuel heater relay are not con­
trolled by the powertrain control module (PCM).
The built-in heater element operates on 12 volts,
300 watts at 0 degrees F.
The fuel heater assembly contains a pre-filter to
prevent contaminants from entering the fuel transfer
pump.