Dodge ram truck 3500 1996 Service Manual page 1238

14 - 4 FUEL SYSTEM
B R
DESCRIPTION AMD OPERATION {Continued)
PLASTIC
LOCKNUT
FUEL FILTER/
FUEL PRESSURE
REGULATOR
FUEL
SUPPLY
CONNECTION
TOP OF
FUEL TANK
PRESSURE RELIEF/
ROLLOVER VALVE
AUXILIARY
FUEL SUPPLY
FITTING
(SOME ENGINES)
PUMP/GAUGE
ELEC. CONNECTION
J9414-32
Fig. 1 Top View Fuel Pump Module—Gas Powered
Engines—Typical
FLOAT
FUEL G A U G E LOCKING
SENDING UNIT TABS
ELECTRIC
FUEL PUMP
MOUNTING
SCREWS
IN-TANK
FUEL FILTER
J9414-33
Fig. 2 Fuel Pump Module Components—Gas
Powered Engines—Typical
operational. Voltage to operate the pump is supplied
through the fuel pump relay.
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 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.
A reed type switch is also used to monitor fuel
level in fuel tank. An electrical signal is sent to the
PCM from this switch to indicate fuel level. The pur­
pose of this feature is to prevent a false setting of
misfire and fuel system monitor trouble codes i f the
fuel level in the tank is less than 15 percent of its
rated capacity. This switch is mounted in the fuel
reservoir within the fuel pump module
FUEL FILTER/FUEL PRESSURE REGULATOR
A combination fuel filter and fuel pressure regula­
tor is used on all engines. I t is pressed into a rubber
grommet located on the top of the fuel pump module
(Fig. 3). A separate frame mounted fuel filter is not
used with any engine.
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 ± 34
kPa (49.2 psi ± 5 psi) at the fuel injectors. I t con­
tains a diaphragm, calibrated springs and a fuel
return valve. The internal fuel filter (Fig. 3) is also
part of the assembly.
INTERNAL
FUEL FILTER
RUBBER
GROMMET
AT PUMP
MODULE
FUEL FILTER/FUEL
PRESSURE REGULATOR
CALIBRATED
SPRINGS
X EXCESS FUEL BACK
TO TANK
FUEL INLET
J9314-170
Fig. 3 Side View—Filter/Regulator
Fuel is supplied to the filter/regulator by the elec­
tric fuel pump through an opening tube at the bot­
tom of filter/regulator (Fig. 3).
The fuel pump module contains a check valve to
maintain some fuel pressure when the engine is not
operating. This will help to start the engine.
If fuel pressure at the pressure regulator exceeds
approximately 49.2 psi, an internal diaphragm closes
and excess fuel pressure is routed back into the tank
through the pressure regulator. A separate fuel
return line is not used with any engine.