2002 JEEP GRAND CHEROKEE Exhaust system

EXHAUST PIPE - 4.7L
REMOVAL
WARNING: IF TORCHES ARE USED WHEN WORK-
ING ON THE EXHAUST SYSTEM, DO NOT ALLOW
THE FLAME NEAR THE FUEL LINES.
WARNING: THE NORMAL OPERATING TEMPERA-
TURE OF THE EXHAUST SYSTEM IS VERY HIGH.
THEREFORE, NEVER WORK AROUND OR ATTEMPT
TO SERVICE ANY PART OF THE EXHAUST SYSTEM
UNTIL IT IS COOLED. SPECIAL CARE SHOULD BE
TAKEN WHEN WORKING NEAR THE CATALYTIC
CONVERTER. THE TEMPERATURE OF THE CON-
VERTER RISES TO A HIGH LEVEL AFTER A SHORT
PERIOD OF ENGINE OPERATION TIME.
(1) Raise and support the vehicle.(2) Saturate the bolts and nuts with heat valve
lubricant. Allow 5 minutes for penetration.
(3) Remove the oxygen sensor from the exhaust
pipe (Fig. 13).
(4) Remove the retaining nuts holding catalytic
converter to exhaust pipe (Fig. 14).
(5) Disconnect the exhaust pipe from the exhaust
manifold. (Fig. 15)
INSPECTION
Discard rusted clamps, broken or worn supports
and attaching parts. Replace a component with orig-
inal equipment parts, or equivalent. This will assure
proper alignment with other parts in the system and
provide acceptable exhaust noise levels.
INSTALLATION
(1) Connect the exhaust pipe to the engine exhaust
manifold. Tighten the nuts (A) to 31 N´m (23 ft. lbs.)
(Fig. 15).
Fig. 13 4.7L Catalytic Converter and O2 Sensor Configuration - 50 State Emissions
11 - 10 EXHAUST SYSTEMWJ

NOTE: When servicing the exhaust system, replace
the factory installed uni-clamp with standard u-bolt
clamps.
(2) Position the catalytic converter onto the
exhaust pipe flange connection. Tighten retaining
nuts to 28 N´m (250 in. lbs.). (Fig. 16)
(3) Coat the oxygen sensor with anti-seize com-
pound. Install the sensor and tighten the nut to 48
N´m (35 ft. lbs.) torque (Fig. 13).
(4) Lower the vehicle.
(5) Start the engine and inspect for exhaust leaks
and exhaust system contact with the body panels.
Adjust the alignment, if needed.
(6) After initial start-up, check the engine exhaust
manifold to exhaust pipe nuts for proper torque.
Fig. 14 Catalytic ConverterÐRemoval
1 - EXHAUST PIPE WITH FLANGE
2 - NUTS (3)
3 - CATALYTIC CONVERTER
Fig. 15 Exhaust Pipe 4.7L
1 - EXHAUST PIPE HANGER
A - NUTS (4)
3 - EXHAUST PIPE
B - BOLTS (4)
Fig. 16 Installing Exhaust Clamps
1 - CATALYTIC CONVERTER
2 - MUFFLER
WJEXHAUST SYSTEM 11 - 11
EXHAUST PIPE - 4.7L (Continued)

HEAT SHIELDS
DESCRIPTION
Heat shields are needed to protect both the vehicle
and the environment from the high temperatures
developed by the catalytic converter. The catalytic
converter releases additional heat into the exhaust
system. Under severe operating conditions, the tem-
perature increases in the area of the converter. Such
conditions can exist when the engine misfires or oth-
erwise does not operate at peak efficiency (Fig. 17).
MUFFLER
DESCRIPTION
Both the 4.0L and 4.7L engines use a stainless
steel muffler to control exhaust noise levels and
exhaust back pressure. The muffler and tailpipe are
a one piece assembly (Fig. 18).
REMOVAL
All original equipment exhaust systems are manu-
factured with the tailpipe welded to the muffler. Ser-
vice replacement mufflers and tailpipes are either
clamped together or welded together.
WARNING: IF TORCHES ARE USED WHEN WORK-
ING ON THE EXHAUST SYSTEM, DO NOT ALLOW
THE FLAME NEAR THE FUEL LINES.
(1) Raise and support the vehicle.
(2) Saturate the bolts and nuts with heat valve
lubricant. Allow 5 minutes for penetration.(3) Loosen the exhaust clamp on the catalytic con-
verter to muffler connection (Fig. 19).
(4) Heat the catalytic converter-to-muffler connec-
tion with a torch until the metal becomes cherry red.
(5) While the metal is still cherry red, remove the
tailpipe/muffler assembly from the catalytic con-
verter.
(6) Remove the tailpipe from the tailpipe hanger
(Fig. 20).
(7) Remove the tailpipe/muffler assembly (Fig. 20).
INSTALLATION
(1) If the tailpipe hanger assembly was removed,
install the hanger to the frame. Tighten the bolts to
22 N´m (192 in. lbs.) torque.
(2) Position the tailpipe and muffler onto the
tailpipe hanger (Fig. 20) .
(3) Install the muffler onto the catalytic converter.
Make sure that the tailpipe has sufficient clearance
from the floor pan. Install exhaust clamp and tighten
the nuts to 47 N´m (35 ft. lbs.) torque (Fig. 19) .
(4) Lower the vehicle.
(5) Start the engine and inspect for exhaust leaks
and exhaust system contact with the body panels.
Adjust the alignment, if needed.
Fig. 17 Front and Rear Floor Pan Heat Shields
Typical
1 - REAR FLOOR PAN HEAT SHIELD
2 - HEAT SHIELD RETAINING NUTS (QTY 8)
3 - FRONT FLOOR PAN HEAT SHIELD
Fig. 18 Muffler and Tailpipe
1 - CATALYTIC CONVERTER
2 - TAILPIPE HANGER
3 - TAILPIPE
4 - MUFFLER
11 - 12 EXHAUST SYSTEMWJ

TAILPIPE
DESCRIPTION
The tailpipe is also made of stainless steel. (Fig.
18) .
OPERATION
The Tailpipe channels the exhaust out of the muf-
fler and out from under the vehicle to control noise
and prevent exhaust gas fumes from entering the
passenger compartment
Fig. 19 Installing Exhaust Clamps
1 - CATALYTIC CONVERTER
2 - MUFFLER
Fig. 20 Muffler and Tailpipe
1 - CATALYTIC CONVERTER
2 - TAILPIPE HANGER
3 - TAILPIPE
4 - MUFFLER
WJEXHAUST SYSTEM 11 - 13
MUFFLER (Continued)

(14) Install air tube (or duct) at top of throttle
body.
(15) Install fuel tank cap.
(16) Connect negative battery cable to battery.
(17) Start engine and check for fuel leaks.
FUEL TANK
DESCRIPTION
The fuel tank is constructed of a plastic material.
Its main functions are for fuel storage and for place-
ment of the fuel pump module and certain ORVR
components.
OPERATION
All models pass a full 360 degree rollover test
without fuel leakage. To accomplish this, fuel and
vapor flow controls are required for all fuel tank con-
nections.
A fuel tank check valve(s) is mounted into the top
of the fuel tank (or pump module). Refer to Fuel
Tank Check Valve for additional information.
An evaporation control system is connected to the
check valve(s) to reduce emissions of fuel vapors into
the atmosphere. When fuel evaporates from the fuel
tank, vapors pass through vent hoses or tubes to a
charcoal canister where they are temporarily held.
When the engine is running, the vapors are drawn
into the intake manifold. Certain models are also
equipped with a self-diagnosing system using a Leak
Detection Pump (LDP). Refer to Emission Control
System for additional information.
Refer to ORVR for On-Board Refueling Vapor
Recovery system information.
REMOVAL
WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT FUEL PRESSURE EVEN WITH ENGINE OFF.
PRESSURE MUST BE RELEASED BEFORE SERVIC-
ING FUEL TANK.
Two different procedures may be used to drain fuel
tank (through ORVR control valve opening at top of
fuel tank, or using DRB scan tool). The quickest is
draining through ORVR control valve opening at top
of fuel tank (Fig. 26).
As an alternative procedure, the electric fuel pump
may be activated allowing tank to be drained at fuel
rail connection. Refer to DRB scan tool for fuel pump
activation procedures. Before disconnecting fuel line
at fuel rail, release fuel pressure. Refer to the Fuel
System Pressure Release Procedure for procedures.
Attach end of Special Adapter Hose Tool number
6539 at fuel rail disconnection. Position opposite end
of 6539 to an approved gasoline draining station.Activate fuel pump with DRB and drain tank until
empty.
If electric fuel pump is not operating, tankMUST
be drained through ORVR control valve opening at
top of fuel tank (Fig. 26).
(1) Release fuel system pressure. Refer to Fuel
System Pressure Release Procedure.
(2) Disconnect negative battery cable at battery.
(3) Raise and support vehicle.
(4) Remove left rear wheel/tire.
CAUTION: HANDLE EVAP, LDP AND ORVR VAPOR /
VACUUM LINES VERY CAREFULLY. THESE LINES
AND HOSES MUST BE FIRMLY CONNECTED.
CHECK THE VAPOR/VACUUM LINES AT THE LDP,
LDP FILTER, EVAP CANISTER, EVAP CANISTER
PURGE SOLENOID AND ORVR COMPONENTS FOR
DAMAGE OR LEAKS. IF A LEAK IS PRESENT, A
DIAGNOSTIC TROUBLE CODE (DTC) MAY BE SET.
(5) Clean top of fuel tank at ORVR control valve
(Fig. 26) or (Fig. 27).
(6) Press release tab in direction of arrow in (Fig.
27) and remove ORVR control valve lock ring
(counter-clockwise). Lift up ORVR control slightly.
Using an approved gasoline draining station, drain
tank until empty through this opening.
(7) Remove stone shield behind left/rear wheel
(Fig. 28). Drill out plastic rivets for removal.
(8) Remove 3 LDP mounting bolts (Fig. 29).
(9) Remove support bracket brace bolt (Fig. 30).
(10) Loosen, but do not remove 2 support bracket
nuts at frame rail (Fig. 29).
(11) To separate and lower front section of two-
piece support bracket, remove 3 attaching bolts on
bottom of support bracket (Fig. 30). While lowering
support bracket, disconnect LDP wiring clip (Fig. 31).
(12) Remove hose clamp (Fig. 32) and remove fuel
fill hose from fuel fill tube.
(13) Cut and discard tie wrap from axle vent hose
(Fig. 32).
(14) Disconnect fuel vent hose from fuel vent tube
(Fig. 32).
(15) Disconnect ORVR hose elbow (Fig. 33) at top
of EVAP canister.
(16) Place hydraulic jack to bottom of fuel tank.
(17) Remove fuel tank-to-rear bumper fascia clips
(Fig. 34).
(18) Remove fuel tank heat shield mounting bolts
(Fig. 35).
CAUTION: To protect fuel tank from exhaust heat,
shield must re-installed after tank installation.
WARNING: PLACE SHOP TOWEL AROUND FUEL
LINES TO CATCH ANY EXCESS FUEL.
WJFUEL DELIVERY 14 - 19
FUEL RAIL (Continued)

(23) Inspect for pinched or leaking fuel tubes/lines.
Inspect for pinched, cracked or leaking fuel hoses.
(24) Inspect for exhaust system restrictions such
as pinched exhaust pipes, collapsed muffler or
plugged catalytic convertor.
(25) If equipped with automatic transmission, ver-
ify electrical harness is firmly connected to park/neu-
tral switch and to transmission components.
(26) Verify fuel pump module pigtail harness elec-
trical connector (Fig. 15) is firmly connected to body
harness connector.
(27) Inspect fuel line harness (from fuel pump
module) at fuel filter/fuel pressure regulator (Fig. 15)
for chaffing, cracks or leaks.
(28) Verify battery cable and solenoid feed wire
connections to starter solenoid are tight and clean.
(29) Inspect for chaffed wires or wires rubbing up
against other components.
(30) Inspect for chaffed vacuum lines or lines rub-
bing up against other components.
Fig. 15 Fuel Filter/Fuel Pressure Regulator Location
1 - FUEL RETURN LINE
2 - FUEL SUPPLY LINE (TO FUEL RAIL)
3 - FUEL FILTER/FUEL PRESSURE REGULATOR
4 - FUEL PRESSURE LINE
5 - REAR AXLE
6 - ELEC. CONNECTOR
7 - EVAP LINE
14 - 38 FUEL INJECTIONWJ
FUEL INJECTION (Continued)

The other two heater elements (downstream sen-
sors 1/2 and 2/2) are controlled by the downstream
heater relay through output signals from the PCM.
To avoid a large simultaneous current surge, power
is delayed to the 2 downstream heater elements by
the PCM for approximately 2 seconds.
REMOVAL
(1) Remove PDC cover.
(2) Remove relay from PDC.
(3) Check condition of relay terminals and PDC
connector terminals for damage or corrosion. Repair
if necessary before installing relay.
(4) Check for pin height (pin height should be the
same for all terminals within the PDC connector).
Repair if necessary before installing relay.
INSTALLATION
(1) Install relay to PDC.
(2) Install cover to PDC.
O2S SENSOR
DESCRIPTION
The Oxygen Sensors (O2S) are attached to, and
protrude into the vehicle exhaust system. Depending
on the emission package, the vehicle may use a total
of either 2 or 4 sensors.
Federal Emissions Package:Two sensors are
used: upstream (referred to as 1/1) and downstream
(referred to as 1/2). With this emission package, the
upstream sensor (1/1) is located just before the main
catalytic convertor. The downstream sensor (1/2) is
located just after the main catalytic convertor.
4.7L V-8 With California Emissions Package:
On this emissions package, 4 sensors are used: 2
upstream (referred to as 1/1 and 2/1) and 2 down-
stream (referred to as 1/2 and 2/2). With this emis-
sion package, the right upstream sensor (2/1) is
located in the right exhaust downpipe just before the
mini-catalytic convertor. The left upstream sensor
(1/1) is located in the left exhaust downpipe just
before the mini-catalytic convertor. The right down-
stream sensor (2/2) is located in the right exhaust
downpipe just after the mini-catalytic convertor, and
before the main catalytic convertor. The left down-
stream sensor (1/2) is located in the left exhaust
downpipe just after the mini-catalytic convertor, and
before the main catalytic convertor.
4.0L 6±Cylinder With California Emissions
Package:On this emissions package, 4 sensors are
used: 2 upstream (referred to as 1/1 and 2/1) and 2
downstream (referred to as 1/2 and 2/2). With this
emission package, the rear/upper upstream sensor
(2/1) is located in the exhaust downpipe just beforethe rear mini-catalytic convertor. The front/upper
upstream sensor (1/1) is located in the exhaust down-
pipe just before the front mini-catalytic convertor.
The rear/lower downstream sensor (2/2) is located in
the exhaust downpipe just after the rear mini-cata-
lytic convertor, and before the main catalytic conver-
tor. The front/lower downstream sensor (1/2) is
located in the exhaust downpipe just after the front
mini-catalytic convertor, and before the main cata-
lytic convertor.
OPERATION
An O2 sensor is a galvanic battery that provides
the PCM with a voltage signal (0-1 volt) inversely
proportional to the amount of oxygen in the exhaust.
In other words, if the oxygen content is low, the volt-
age output is high; if the oxygen content is high the
output voltage is low. The PCM uses this information
to adjust injector pulse-width to achieve the
14.7±to±1 air/fuel ratio necessary for proper engine
operation and to control emissions.
The O2 sensor must have a source of oxygen from
outside of the exhaust stream for comparison. Cur-
rent O2 sensors receive their fresh oxygen (outside
air) supply through the O2 sensor case housing.
Four wires (circuits) are used on each O2 sensor: a
12±volt feed circuit for the sensor heating element; a
ground circuit for the heater element; a low-noise
sensor return circuit to the PCM, and an input cir-
cuit from the sensor back to the PCM to detect sen-
sor operation.
Oxygen Sensor Heaters/Heater Relays:
Depending on the emissions package, the heating ele-
ments within the sensors will be supplied voltage
from either the ASD relay, or 2 separate oxygen sen-
sor relays. Refer to Wiring Diagrams to determine
which relays are used.
The O2 sensor uses a Positive Thermal Co-efficient
(PTC) heater element. As temperature increases,
resistance increases. At ambient temperatures
around 70ÉF, the resistance of the heating element is
approximately 4.5 ohms on 4.0L engines. It is
approximately 13.5 ohms on the 4.7L engine. As the
sensor's temperature increases, resistance in the
heater element increases. This allows the heater to
maintain the optimum operating temperature of
approximately 930É-1100ÉF (500É-600É C). Although
the sensors operate the same, there are physical dif-
ferences, due to the environment that they operate
in, that keep them from being interchangeable.
Maintaining correct sensor temperature at all
times allows the system to enter into closed loop
operation sooner. Also, it allows the system to remain
in closed loop operation during periods of extended
idle.
14 - 50 FUEL INJECTIONWJ
O2S HEATER RELAY (Continued)

In Closed Loop operation, the PCM monitors cer-
tain O2 sensor input(s) along with other inputs, and
adjusts the injector pulse width accordingly. During
Open Loop operation, the PCM ignores the O2 sensor
input. The PCM adjusts injector pulse width based
on preprogrammed (fixed) values and inputs from
other sensors.
Upstream Sensor (Non-California Emissions):
The upstream sensor (1/1) provides an input voltage
to the PCM. The input tells the PCM the oxygen con-
tent of the exhaust gas. The PCM uses this informa-
tion to fine tune fuel delivery to maintain the correct
oxygen content at the downstream oxygen sensor.
The PCM will change the air/fuel ratio until the
upstream sensor inputs a voltage that the PCM has
determined will make the downstream sensor output
(oxygen content) correct.
The upstream oxygen sensor also provides an input
to determine catalytic convertor efficiency.
Downstream Sensor (Non-California Emis-
sions):The downstream oxygen sensor (1/2) is also
used to determine the correct air-fuel ratio. As the
oxygen content changes at the downstream sensor,
the PCM calculates how much air-fuel ratio change is
required. The PCM then looks at the upstream oxy-
gen sensor voltage and changes fuel delivery until
the upstream sensor voltage changes enough to cor-
rect the downstream sensor voltage (oxygen content).
The downstream oxygen sensor also provides an
input to determine catalytic convertor efficiency.
Upstream Sensors (California Engines):Tw o
upstream sensors are used (1/1 and 2/1). The 1/1 sen-
sor is the first sensor to receive exhaust gases from
the #1 cylinder. They provide an input voltage to the
PCM. The input tells the PCM the oxygen content of
the exhaust gas. The PCM uses this information to
fine tune fuel delivery to maintain the correct oxygen
content at the downstream oxygen sensors. The PCM
will change the air/fuel ratio until the upstream sen-
sors input a voltage that the PCM has determined
will make the downstream sensors output (oxygen
content) correct.
The upstream oxygen sensors also provide an input
to determine mini-catalyst efficiency. Main catalytic
convertor efficiency is not calculated with this pack-
age.
Downstream Sensors (California Engines):
Two downstream sensors are used (1/2 and 2/2). The
downstream sensors are used to determine the cor-
rect air-fuel ratio. As the oxygen content changes at
the downstream sensor, the PCM calculates how
much air-fuel ratio change is required. The PCM
then looks at the upstream oxygen sensor voltage,
and changes fuel delivery until the upstream sensor
voltage changes enough to correct the downstream
sensor voltage (oxygen content).The downstream oxygen sensors also provide an
input to determine mini-catalyst efficiency. Main cat-
alytic convertor efficiency is not calculated with this
package.
Engines equipped with either a downstream sen-
sor(s), or a post-catalytic sensor, will monitor cata-
lytic convertor efficiency. If efficiency is below
emission standards, the Malfunction Indicator Lamp
(MIL) will be illuminated and a Diagnostic Trouble
Code (DTC) will be set. Refer to Monitored Systems
in Emission Control Systems for additional informa-
tion.
REMOVAL
Never apply any type of grease to the oxygen
sensor electrical connector, or attempt any sol-
dering of the sensor wiring harness.
Oxygen sensor (O2S) locations are shown in (Fig.
33) and (Fig. 34).
WARNING: THE EXHAUST MANIFOLD, EXHAUST
PIPES AND CATALYTIC CONVERTER(S) BECOME
VERY HOT DURING ENGINE OPERATION. ALLOW
ENGINE TO COOL BEFORE REMOVING OXYGEN
SENSOR.
(1) Raise and support vehicle.
(2) Disconnect O2S pigtail harness from main wir-
ing harness.
(3) If equipped, disconnect sensor wire harness
mounting clips from engine or body.
CAUTION: When disconnecting sensor electrical
connector, do not pull directly on wire going into
sensor.
(4) Remove O2S sensor with an oxygen sensor
removal and installation tool.
INSTALLATION
Threads of new oxygen sensors are factory coated
with anti-seize compound to aid in removal.DO
NOT add any additional anti-seize compound to
threads of a new oxygen sensor.
(1) Install O2S sensor. Tighten to 30 N´m (22 ft.
lbs.) torque.
(2) Connect O2S sensor wire connector to main
wiring harness.
(3) If equipped, connect sensor wire harness
mounting clips to engine or body.When Equipped:
The O2S pigtail harness must be clipped and/or
bolted back to their original positions on
engine or body to prevent mechanical damage
to wiring..
(4) Lower vehicle.
WJFUEL INJECTION 14 - 51
O2S SENSOR (Continued)