Dodge ram truck 3500 1996 Service Manual page 1306

S E S C R i P T g & H mm O P E R A T I O N ccomtmued)
FUEL HEATER RELAY
Voltage to operate the fuel heater is supplied from
the ignition switch through the fuel heater relay. The
powertrain control module (PCM) is not used to con­
trol this relay.
The fuel heater relay is located in the engine com­
partment near the brake master cylinder (Fig. 5).
FUEL HEATER
RELAY
\
FUEL SHUT-OFF
SOLENOID RELAY
BRAKE MASTER
CYLINDER
J9414-31
Fig. 5 Fuel Heater Relay—Diesei
FUEL TRANSFER PUMP
The fuel transfer pump (fuel lift pump) is located
on the left-rear side of the engine cylinder block
above the starter motor (Fig. 1). This mechanically
operated pump is not controlled by the powertrain
control module (PCM).
The purpose of the fuel transfer pump is to supply
(transfer) a low-pressure fuel source of approximately
172 Kpa (25 psi) to the injection pump and fuel filter/
water separator from the fuel tank. Here, the low-
pressure is raised by the fuel injection pump for
operation of the high-pressure fuel injectors. The
transfer pump is driven by an eccentric on the engine
camshaft that actuates a spring loaded piston within
the pump (Fig. 6). Check valves within the pump,
control direction of fuel flow and prevent fuel bleed-
back during engine shut down.
The fuel transfer pump should never be operated
without the pre-filter installed.
The fuel volume of the transfer pump will vary
with engine rpm, but will always provide more fuel
than the fuel injection pump requires. Excess fuel is
returned to the fuel tank through an overflow valve.
The valve is located on the side of the injection pump
(Fig. 7) and is used to connect the fuel return line to
the side of the injection pump. This valve opens at
approximately 152 kPa (22 psi) and returns fuel to
the fuel tank through the fuel return line.
CHECK
VALVES
A I C
LOW PRESSURE
SUPPLY UNE
RUBBER
PRIMER PUMP
BUTTON
ENGINE
CAMSHAFT
/
FUEL LINE
INLET
Fig. 6 Transfer Pump Operation
FUEL RETURN LINE
J 9 4 1 4 - 7 1
OVERFLOW
VALVE
FUEL INJECTION
PUMP
J9414-102
Fig. 7 Injection Pump Overflow Valve
The transfer pump has a primer button (Fig. 8).
This rubber primer button is located on the pump
housing. The purpose of the button is to prime and
bleed air from the fuel system i f the vehicle has run
out of fuel. To prime the system up to the fuel injec­
tor pump, continually press on the button (Fig. 8)
until resistance is felt. This resistance will indicate
that priming is completed and air has been removed.
I f the primer button feels as i f it is not pumping,
rotate (crank) the engine approximately 90 degrees.
This will position the engine camshaft lobe away