Content .. 368 369 370 371 ..

Jeep Grand Cherokee WJ. Manual - part 370

2000 JEEP GRAND CHEROKEE

FUEL SYSTEM

TABLE OF CONTENTS

page

FUEL DELIVERY SYSTEM. . . . . . . . . . . . . . . . . . . . 1

FUEL INJECTION SYSTEM . . . . . . . . . . . . . . . . . . 30

FUEL DELIVERY SYSTEM

TABLE OF CONTENTS

page

DESCRIPTION AND OPERATION

ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

FUEL INJECTOR RAIL—4.7L ENGINE . . . . . . . . . . 5
FUEL TANK FILLER TUBE CAP . . . . . . . . . . . . . . . 6
FUEL TUBES/LINES/HOSES AND CLAMPS . . . . . . 6
QUICK-CONNECT FITTINGS . . . . . . . . . . . . . . . . . 7

DIAGNOSIS AND TESTING

FUEL PUMP PRESSURE TEST . . . . . . . . . . . . . . . 7
FUEL PUMP CAPACITY TEST . . . . . . . . . . . . . . . . 9
FUEL PRESSURE LEAK DOWN TEST . . . . . . . . . . 9
FUEL PUMP AMPERAGE TEST . . . . . . . . . . . . . . 11
FUEL GAUGE SENDING UNIT . . . . . . . . . . . . . . . 11
FUEL INJECTOR TEST . . . . . . . . . . . . . . . . . . . . 12

SERVICE PROCEDURES

FUEL SYSTEM PRESSURE RELEASE

PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . 12

QUICK-CONNECT FITTINGS . . . . . . . . . . . . . . . . 13

REMOVAL AND INSTALLATION

FUEL FILTER/FUEL PRESSURE REGULATOR . . . 15
FUEL PUMP MODULE . . . . . . . . . . . . . . . . . . . . . 16
FUEL PUMP INLET FILTER . . . . . . . . . . . . . . . . . 17
FUEL GAUGE SENDING UNIT . . . . . . . . . . . . . . . 18
FUEL INJECTOR RAIL/FUEL DAMPER—4.0L

ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

FUEL INJECTOR RAIL—4.7L V–8 ENGINE. . . . . . 20
FUEL INJECTORS . . . . . . . . . . . . . . . . . . . . . . . . 21
FUEL TANK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
FUEL TANK FILLER TUBE CAP . . . . . . . . . . . . . . 25
ACCELERATOR PEDAL . . . . . . . . . . . . . . . . . . . . 25
THROTTLE CABLE—4.0L ENGINE. . . . . . . . . . . . 25
THROTTLE CABLE—4.7L V-8 ENGINE. . . . . . . . . 26

SPECIFICATIONS

FUEL TANK CAPACITY . . . . . . . . . . . . . . . . . . . . 27
FUEL SYSTEM PRESSURE . . . . . . . . . . . . . . . . . 27
FUEL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . 27
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . . 29

DESCRIPTION AND OPERATION

PCM VIN REPROGRAMMING

OPERATION

USE THE DRB SCAN TOOL TO REPROGRAM

THE NEW POWERTRAIN CONTROL MODULE
(PCM) WITH THE VEHICLES ORIGINAL IDEN-
TIFICATION NUMBER (VIN) AND THE VEHI-
CLES ORIGINAL MILEAGE. IF THIS STEP IS

NOT DONE, A DIAGNOSTIC TROUBLE CODE
(DTC) MAY BE SET.

FUEL DELIVERY SYSTEM

DESCRIPTION

The fuel delivery system consists of:
• the fuel pump module containing the electric

fuel pump, fuel gauge sending unit (fuel level sensor)
and a separate fuel filter located at bottom of pump
module

FUEL SYSTEM

14 - 1

• a separate combination fuel filter/fuel pressure

regulator

• fuel tubes/lines/hoses

• quick-connect fittings

• fuel injector rail

• fuel injectors

• fuel tank

• fuel tank filler/vent tube assembly

• fuel tank filler tube cap

• accelerator pedal

• throttle cable

OPERATION

The fuel tank assembly consists of: the fuel tank,

fuel tank shield, fuel tank straps, fuel pump module
assembly, fuel pump module locknut/gasket, and roll-
over valve (refer to Emission Control System for roll-
over valve information).

A fuel filler/vent tube assembly using a pressure/

vacuum, 1/4 turn fuel filler cap is used. The fuel
filler tube contains a flap door located below the fuel
fill cap.

Also to be considered part of the fuel system is the

evaporation control system. This is designed to
reduce the emission of fuel vapors into the atmo-
sphere. The description and function of the Evapora-
tive Control System is found in Emission Control
Systems.

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.

FUEL PUMP MODULE

DESCRIPTION

The fuel pump module is installed in the top of the

fuel tank (Fig. 1). The fuel pump module (Fig. 2) con-
tains the following components:

• A separate fuel pick-up filter (strainer)

• An electric fuel pump

• A threaded locknut to retain module to tank

• A gasket between tank flange and module

• Fuel gauge sending unit (fuel level sensor)

• Fuel supply tube (line) connection

• Fuel return tube (line) connection
The fuel gauge sending unit and pick-up filter may

be serviced separately. If the electrical fuel pump
requires service, the entire fuel pump module must
be replaced.

OPERATION

Refer to Fuel Pump, Fuel Filter/Fuel Pressure Reg-

ulator and Fuel Gauge Sending Unit.

FUEL PUMP

DESCRIPTION

The fuel pump is located inside of the fuel pump

module. A 12 volt, permanent magnet, electric motor
powers the fuel pump.

OPERATION

Voltage to operate the electric pump is supplied

through the fuel pump relay.

Fuel is drawn in through a filter at the bottom of

the module and pushed through the electric motor
gearset to the pump outlet.

Check Valve Operation: The pump outlet con-

tains a one-way check valve to prevent fuel flow back
into the tank and to maintain fuel supply line pres-
sure (engine warm) when pump is not operational. It
is also used to keep the fuel supply line full of gaso-
line when pump is not operational. After the vehicle
has cooled down, fuel pressure may drop to 0 psi
(cold fluid contracts), but liquid gasoline will remain
in fuel supply line between the check valve and fuel
injectors. Fuel pressure that has dropped to 0

Fig. 1 Fuel Tank/Fuel Pump Module Location (Top

View)

1 – FUEL PUMP MODULE
2 – LOCKNUT
3 – ROLL OVER VALVE
4 – FUEL FILL HOSE
5 – FUEL VENT HOSE
6 – FUEL TANK
7 – FUEL SUPPLY (PRESSURE) LINE
8 – FUEL RETURN LINE
9 – CLAMPS

14 - 2

FUEL SYSTEM

DESCRIPTION AND OPERATION (Continued)

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

The combination fuel filter/pressure regulator is

located in front of the fuel tank and above the rear
axle (Fig. 3). It is transversely mounted to a chassis
crossmember (left-to-right). Fuel Line Identifica-
tion: The filter/regulator is equipped with 3 fuel line
fittings (2 at one end and 1 at the other end). The
single fitting facing the left side of the vehicle is the
supply line to the fuel rail (Fig. 3). The 2 fittings fac-
ing the right side of the vehicle are connected to the
fuel tank. Of these 2 fittings, the fitting towards the
front is used for fuel return to the fuel tank. The fit-
ting towards the rear is a pressure line.

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

6 34

kPa (49.2 psi

6 5 psi) at the fuel injectors. It con-

tains a diaphragm, calibrated springs and a fuel

Fig. 2 Fuel Pump Module Components

1 – FUEL PUMP MODULE
2 – FUEL GAUGE FLOAT
3 – ELECTRIC FUEL PUMP
4 – INLET FILTER
5 – FUEL GAUGE SENDING UNIT
6 – PIGTAIL HARNESS

FUEL SYSTEM

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DESCRIPTION AND OPERATION (Continued)

Content .. 368 369 370 371 ..