Engine number JEEP LIBERTY 2002 KJ / 1.G Repair Manual

OPERATION
Fuel is picked up in the fuel tank by the fuel pump
module. This module is located on the bottom of the
fuel tank.
A fuel return system is provided within the fuel
pump module using check valves. A separate fuel
return line from the engine to the tank is not used.
The fuel pressure regulator and the main fuel filter
are not combined. They are separate items.
The fuel tank assembly consists of: the fuel tank,
fuel pump module assembly, fuel pump module lock
ring/gasket, ORVR components. Refer to 25, Emis-
sion Control System for ORVR 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. A one-way check valve is installed into the
tanks fuel fill fitting.
Also to be considered part of the fuel system is the
evaporation control system and ORVR system. This
is designed to reduce the emission of fuel vapors into
the atmosphere. The description and function of the
Evaporative Control System is found in 25, Emission
Control Systems.
Both fuel filters (mounted to front of fuel tank, and
inside the bottom fuel pump module) are designed for
extended service. They do not require normal sched-
uled maintenance. The bottom section of the fuel
pump module (with included filter) should only be
replaced if a diagnostic procedure indicates to do so.
Also, the fuel filter mounted to the front of the fuel
tank should only be replaced if a diagnostic proce-
dure indicates to do so.
DIAGNOSIS AND TESTING - FUEL PRESSURE
LEAK DOWN TEST
Use this test in conjunction with the Fuel Pump
Pressure Test and Fuel Pump Capacity Test.
Check Valve Operation:The electric fuel pump
outlet contains a one-way check valve to prevent fuel
flow back into the tank and to maintain fuel supply
line pressure (engine warm) when pump is not oper-
ational. It is also used to keep the fuel supply line
full of gasoline 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 psi on a cooled down vehicle
(engine off) is a normal condition.When the elec-
tric fuel pump is activated, fuel pressure should
immediately(1±2 seconds) rise to specification.
Abnormally long periods of cranking to restart a
hotengine that has been shut down for a short
period of time may be caused by:
²Fuel pressure bleeding past a fuel injector(s).²Fuel pressure bleeding past the check valve in
the fuel pump module.
(1) Disconnect the fuel inlet line at fuel rail. Refer
to Quick Connect Fittings for procedures. On some
engines, air cleaner housing removal may be neces-
sary before fuel line disconnection.
(2) Obtain correct Fuel Line Pressure Test Adapter
Tool Hose. Tool number 6539 is used for 5/16º fuel
lines and tool number 6631 is used for 3/8º fuel lines.
(3) Connect correct Fuel Line Pressure Test
Adapter Tool Hose between disconnected fuel line
and fuel rail (Fig. 2).
(4) Connect the 0-414 kPa (0-60 psi) fuel pressure
test gauge (from Gauge Set 5069) to the test port on
the appropriate Adaptor Tool.The DRBtIII Scan
Tool along with the PEP module, the 500 psi
pressure transducer, and the transducer-to-test
port adapter may also be used in place of the
fuel pressure gauge.
The fittings on both tools must be in good
condition and free from any small leaks before
performing the proceeding test.
(5) Start engine and bring to normal operating
temperature.
(6) Observe test gauge. Normal operating pressure
should be 339 kPa +/±34 kPa (49.2 psi +/±5 psi).
(7) Shut engine off.
Fig. 2 CONNECTING ADAPTER TOOLÐTYPICAL
1 - VEHICLE FUEL LINE
2 - TEST PORT ªTº
3 - SPECIAL TOOL 6923, 6631, 6541 OR 6539
4 - FUEL PRESSURE TEST GAUGE
5 - FUEL LINE CONNECTION AT RAIL
6 - FUEL RAIL
KJFUEL DELIVERY 14 - 3
FUEL DELIVERY (Continued)

(b) After disconnection, plastic retainer ring will
remain with quick-connect fitting connector body.
(c) Inspect fitting connector body, plastic retainer
ring and fuel system component for damage.
Replace as necessary.
(8)Latch Clips:Depending on vehicle model and
engine, 2 different types of safety latch clips are used
(Fig. 16) or (Fig. 17). Type-1 is tethered to fuel line
and type-2 is not. A special tool will be necessary todisconnect fuel line after latch clip is removed. The
latch clip may be used on certain fuel line/fuel rail
connection, or to join fuel lines together.
(a) Type 1: Pry up on latch clip with a screw-
driver (Fig. 16).
(b) Type 2: Separate and unlatch 2 small arms
on end of clip (Fig. 17) and swing away from fuel
line.
(c) Slide latch clip toward fuel rail while lifting
with screwdriver.
(d) Insert special fuel line removal tool (Snap-On
number FIH 9055-1 or equivalent) into fuel line
(Fig. 18). Use tool to release locking fingers in end
of line.
(e) With special tool still inserted, pull fuel line
from fuel rail.
(f) After disconnection, locking fingers will
remain within quick-connect fitting at end of fuel
line.
(9) Disconnect quick-connect fitting from fuel sys-
tem component being serviced.
CONNECTING
(1) Inspect quick-connect fitting body and fuel sys-
tem component for damage. Replace as necessary.
(2) Prior to connecting quick-connect fitting to
component being serviced, check condition of fitting
and component. Clean parts with a lint-free cloth.
Lubricate with clean engine oil.
(3) Insert quick-connect fitting into fuel tube or
fuel system component until built-on stop on fuel
tube or component rests against back of fitting.
(4) Continue pushing until a click is felt.
(5) Single-tab type fitting: Push new tab down
until it locks into place in quick-connect fitting.
(6) Verify a locked condition by firmly pulling on
fuel tube and fitting (15-30 lbs.).
(7) Latch Clip Equipped: Install latch clip (snaps
into position).If latch clip will not fit, this indi-
cates fuel line is not properly installed to fuel
rail (or other fuel line). Recheck fuel line con-
nection.
(8) Connect negative cable to battery.
(9) Start engine and check for leaks.
FUEL PRESSURE REGULATOR
DESCRIPTION
The fuel pressure regulator is located on the bot-
tom of the upper section of the fuel pump module.
The fuel filteris not combinedinto the pressure
regulator on this model.
Fig. 17 LATCH CLIP-TYPE 2
1 - LATCH CLIP
Fig. 18 FUEL LINE DISCONNECTION USING
SPECIAL TOOL
1 - SPECIAL FUEL LINE TOOL
2 - FUEL LINE
3 - FUEL RAIL
KJFUEL DELIVERY 14 - 13
QUICK CONNECT FITTING (Continued)

FUEL PUMP
DESCRIPTION
The electric fuel pump is located inside of the fuel
pump module. A 12 volt, permanent magnet, electric
motor powers the fuel pump. The electric fuel pump
is not a separate, serviceable component.
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 bottom section of
the fuel pump module contains a one-way check
valve to prevent fuel flow back into the tank and to
maintain fuel supply line pressure (engine warm)
when pump is not operational. It is also used to keep
the fuel supply line full of gasoline 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 psi on a cooled
down vehicle (engine off) is a normal condition.
Refer to the Fuel Pressure Leak Down Test for more
information.
The electric fuel pump is not a separate, service-
able component.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - FUEL PUMP
CAPACITY TEST
Before performing this test, verify fuel pump
pressure. Refer to Fuel Pump Pressure Test.
Use this test in conjunction with the Fuel Pres-
sure Leak Down Test.
(1) Release fuel system pressure. Refer to Fuel
Pressure Release Procedure.
(2) Disconnect fuel supply line at fuel rail. Refer to
Quick-Connect Fittings. Some engines may require
air cleaner housing removal before line disconnection.
(3) Obtain correct Fuel Line Pressure Test Adapter
Tool Hose. Tool number 6539 is used for 5/16º fuel
lines and tool number 6631 is used for 3/8º fuel lines.
(4) Connect correct Fuel Line Pressure Test
Adapter Tool Hose into disconnected fuel supply line.
Insert other end of Adaptor Tool Hose into a gradu-
ated container.
(5) Remove fuel fill cap.(6) To activate fuel pump and pressurize system,
obtain DRBtscan tool and actuate ASD Fuel System
Test.
(7) A good fuel pump will deliver at least 1/10 liter
of fuel in 7 seconds. Do not operate fuel pump for
longer than 7 seconds with fuel line disconnected as
fuel pump module reservoir may run empty.
(a) If capacity is lower than specification, but
fuel pump can be heard operating through fuel fill
cap opening, check for a kinked/damaged fuel sup-
ply line somewhere between fuel rail and fuel
pump module.
(b) If line is not kinked/damaged, and fuel pres-
sure is OK, but capacity is low, replace fuel filter.
Refer to Fuel Filter Removal/Installation for addi-
tional information.
(c) If both fuel pressure and capacity are low,
replace bottom section of fuel pump module. Refer
to Fuel Pump Module Removal/Installation.
DIAGNOSIS AND TESTING - FUEL PUMP
PRESSURE TEST
Use this test in conjunction with the Fuel Pump
Capacity Test, Fuel Pressure Leak Down Test and
Fuel Pump Amperage Test found elsewhere in this
group.
Check Valve Operation:The bottom section of
the fuel pump module contains a one-way check
valve to prevent fuel flow back into the tank and to
maintain fuel supply line pressure (engine warm)
when pump is not operational. It is also used to keep
the fuel supply line full of gasoline 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 psi on a cooled
down vehicle (engine off) is a normal condition.
When the electric fuel pump is activated, fuel pres-
sure shouldimmediately(1±2 seconds) rise to spec-
ification.
The fuel system is equipped with a separate fuel
pump module mounted, fuel pressure regulator. The
fuel filter is remotely mounted. The fuel pressure
regulator is not controlled by engine vacuum.
WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT FUEL PRESSURE EVEN WITH THE ENGINE
OFF. BEFORE DISCONNECTING FUEL LINE AT
FUEL RAIL, THIS PRESSURE MUST BE RELEASED.
REFER TO THE FUEL SYSTEM PRESSURE
RELEASE PROCEDURE.
KJFUEL DELIVERY 14 - 15

WARNING: BEFORE PROCEEDING TO NEXT STEP,
NOTE THE FUEL PUMP WILL BE ACTIVATED AND
SYSTEM PRESSURE WILL BE PRESENT. THIS WILL
OCCUR AFTER CONNECTING TEST LEADS FROM
LCS ADAPTER INTO FUEL PUMP RELAY CAVITIES.
THE FUEL PUMP WILL OPERATE EVEN WITH IGNI-
TION KEY IN OFF POSITION. BEFORE ATTACHING
TEST LEADS, BE SURE ALL FUEL LINES AND
FUEL SYSTEM COMPONENTS ARE CONNECTED.
CAUTION: To prevent possible damage to the vehi-
cle electrical system and LCS adapter, the test
leads must be connected into relay cavities exactly
as shown in following steps.
Depending upon vehicle model, year or engine con-
figuration, three different types of relays may be
used: Type-1, type-2 and type±3.
(14) If equipped withtype±1 relay(Fig. 22),
attach test leads from LCS adapter into PDC relay
cavities number 30 and 87. For location of these cav-
ities, refer to numbers stamped to bottom of relay
(Fig. 22).
(15) If equipped withtype±2 relay(Fig. 23),
attach test leads from LCS adapter into PDC relay
cavities number 30 and 87. For location of these cav-
ities, refer to numbers stamped to bottom of relay
(Fig. 23).
(16) If equipped withtype±3 relay(Fig. 24),
attach test leads from LCS adapter into PDC relay
cavities number 3 and 5. For location of these cavi-
ties, refer to numbers stamped to bottom of relay
(Fig. 24).
Fig. 22 FUEL PUMP RELAY - TYPE 1
Fig. 23 FUEL PUMP RELAY - TYPE 2
TERMINAL LEGEND
NUMBER IDENTIFICATION
30 COMMON FEED
85 COIL GROUND
86 COIL BATTERY
87 NORMALLY OPEN
87A NORMALLY CLOSED
Fig. 24 FUEL PUMP RELAY - TYPE 3
TERMINAL LEGEND
NUMBER IDENTIFICATION
1 COIL BATTERY
2 COIL GROUND
3 COMMON FEED
4 NORMALLY CLOSED
5 NORMALLY OPEN
KJFUEL DELIVERY 14 - 17
FUEL PUMP (Continued)

REMOVAL
Fuel Tank Draining
WARNING: THE FUEL SYSTEM MAY BE UNDER
CONSTANT FUEL PRESSURE EVEN WITH THE
ENGINE OFF. THIS PRESSURE MUST BE
RELEASED BEFORE SERVICING FUEL TANK.
Two different procedures may be used to drain fuel
tank: removing fuel pump module access plate, or
using DRBtscan tool. Due to a one-way check valve
installed into the fuel fill opening fitting at the tank
(Fig. 38), the tank cannot be drained conventionally
at the fill cap.
The quickest draining procedure involves removing
fuel pump module access plate.
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 test hose tool number 6541,
6539, 6631 or 6923 at fuel rail disconnection (tool
number will depend on model and/or engine applica-
tion). Position opposite end of this hose tool to an
approved gasoline draining station. Activate fuel
pump and drain tank until empty.
If electric fuel pump is not operating, fuel pump
module access plate must be removed for fuel drain-
ing. Refer to following procedures.Fuel tank removal will not be necessary for
fuel tank draining. Access for draining is from
rear cargo area.
(1) Open all windows in vehicle to allow for air
ventilation.
(2) Four cargo holdown clamps are located inside
the vehicle on the floor of the rear cargo area.
Remove the 2 rearward mounted clamps by drilling
out the clamp rivets.
(3) Fold carpeting forward to gain access to fuel
pump module access plate (Fig. 39).
(4) Remove 4 fuel pump module access plate nuts
(Fig. 39).
(5) While applying heat from a heat gun, carefully
pry up fuel pump module access plate. Take care not
to bend plate.
(6) Thoroughly clean area around top of pump
module to prevent contaminants from entering fuel
tank or fuel lines.
(7) Release fuel system pressure.
(8) Disconnect 2 fuel lines (Fig. 40) at fuel pump
module by pressing on tabs at side of fitting.
(9) Disconnect electrical connector (Fig. 40). Slide
red tab first to unlock, and push grey tab down for
removal.
(10) Disconnect ORVR hose (Fig. 40) at pump mod-
ule fitting.
Fig. 38 FUEL FILL CHECK VALVE
1 - ONE-WAY CHECK VALVE
2 - FUEL FILL FITTING
3 - SIDE OF FUEL TANK
Fig. 39 ACCESS PLATE
1 - FLOORPAN AT REAR
2 - FUEL PUMP MODULE ACCESS PLATE
3 - NUTS (4)
4 - OPENING TO PUMP MODULE
KJFUEL DELIVERY 14 - 25
FUEL TANK (Continued)

FUEL INJECTOR
DESCRIPTION
An individual fuel injector (Fig. 9) is used for each
individual cylinder.
OPERATION
OPERATION - FUEL INJECTOR
The top (fuel entry) end of the injector (Fig. 9) is
attached into an opening on the fuel rail.
The fuel injectors are electrical solenoids. The
injector contains a pintle that closes off an orifice at
the nozzle end. When electric current is supplied to
the injector, the armature and needle move a short
distance against a spring, allowing fuel to flow out
the orifice. Because the fuel is under high pressure, a
fine spray is developed in the shape of a pencil
stream. The spraying action atomizes the fuel, add-
ing it to the air entering the combustion chamber.
The nozzle (outlet) ends of the injectors are posi-
tioned into openings in the intake manifold just
above the intake valve ports of the cylinder head.
The engine wiring harness connector for each fuel
injector is equipped with an attached numerical tag
(INJ 1, INJ 2 etc.). This is used to identify each fuel
injector.
The injectors are energized individually in a
sequential order by the Powertrain Control Module(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage is supplied to the injectors through
the ASD relay.
The PCM determines injector pulse width based on
various inputs.
OPERATION - PCM OUTPUT
The nozzle ends of the injectors are positioned into
openings in the intake manifold just above the intake
valve ports of the cylinder head. The engine wiring
harness connector for each fuel injector is equipped
with an attached numerical tag (INJ 1, INJ 2 etc.).
This is used to identify each fuel injector with its
respective cylinder number.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage (12 volts +) is supplied to the injec-
tors through the ASD relay. The ASD relay will shut-
down the 12 volt power source to the fuel injectors if
the PCM senses the ignition is on, but the engine is
not running. This occurs after the engine has not
been running for approximately 1.8 seconds.
The PCM determines injector on-time (pulse width)
based on various inputs.
DIAGNOSIS AND TESTING - FUEL INJECTOR
To perform a complete test of the fuel injectors and
their circuitry, use the DRB scan tool and refer to the
appropriate Powertrain Diagnostics Procedures man-
ual. To test the injector only, refer to the following:
Disconnect the fuel injector wire harness connector
from the injector. The injector is equipped with 2
electrical terminals (pins). Place an ohmmeter across
the terminals. Resistance reading should be approxi-
mately 12 ohms  1.2 ohms at 20ÉC (68ÉF).
Fig. 9 FUEL INJECTOR Ð TYPICAL
KJFUEL INJECTION 14 - 33

IDLE AIR CONTROL MOTOR
DESCRIPTION
The IAC stepper motor is mounted to the throttle
body, and regulates the amount of air bypassing the
control of the throttle plate. As engine loads and
ambient temperatures change, engine rpm changes.
A pintle on the IAC stepper motor protrudes into a
passage in the throttle body, controlling air flow
through the passage. The IAC is controlled by the
Powertrain Control Module (PCM) to maintain the
target engine idle speed.
OPERATION
At idle, engine speed can be increased by retract-
ing the IAC motor pintle and allowing more air to
pass through the port, or it can be decreased by
restricting the passage with the pintle and diminish-
ing the amount of air bypassing the throttle plate.
The IAC is called a stepper motor because it is
moved (rotated) in steps, or increments. Opening the
IAC opens an air passage around the throttle blade
which increases RPM.
The PCM uses the IAC motor to control idle speed
(along with timing) and to reach a desired MAP dur-
ing decel (keep engine from stalling).
The IAC motor has 4 wires with 4 circuits. Two of
the wires are for 12 volts and ground to supply elec-
trical current to the motor windings to operate the
stepper motor in one direction. The other 2 wires are
also for 12 volts and ground to supply electrical cur-
rent to operate the stepper motor in the opposite
direction.
To make the IAC go in the opposite direction, the
PCM just reverses polarity on both windings. If only
1 wire is open, the IAC can only be moved 1 step
(increment) in either direction. To keep the IAC
motor in position when no movement is needed, the
PCM will energize both windings at the same time.
This locks the IAC motor in place.
In the IAC motor system, the PCM will count
every step that the motor is moved. This allows the
PCM to determine the motor pintle position. If the
memory is cleared, the PCM no longer knows the
position of the pintle. So at the first key ON, the
PCM drives the IAC motor closed, regardless of
where it was before. This zeros the counter. Fromthis point the PCM will back out the IAC motor and
keep track of its position again.
When engine rpm is above idle speed, the IAC is
used for the following:
²Off-idle dashpot (throttle blade will close quickly
but idle speed will not stop quickly)
²Deceleration air flow control
²A/C compressor load control (also opens the pas-
sage slightly before the compressor is engaged so
that the engine rpm does not dip down when the
compressor engages)
²Power steering load control
The PCM can control polarity of the circuit to con-
trol direction of the stepper motor.
IAC Stepper Motor Program:The PCM is also
equipped with a memory program that records the
number of steps the IAC stepper motor most recently
advanced to during a certain set of parameters. For
example: The PCM was attempting to maintain a
1000 rpm target during a cold start-up cycle. The last
recorded number of steps for that may have been
125. That value would be recorded in the memory
cell so that the next time the PCM recognizes the
identical conditions, the PCM recalls that 125 steps
were required to maintain the target. This program
allows for greater customer satisfaction due to
greater control of engine idle.
Another function of the memory program, which
occurs when the power steering switch (if equipped),
or the A/C request circuit, requires that the IAC step-
per motor control engine rpm, is the recording of the
last targeted steps into the memory cell. The PCM
can anticipate A/C compressor loads. This is accom-
plished by delaying compressor operation for approx-
imately 0.5 seconds until the PCM moves the IAC
stepper motor to the recorded steps that were loaded
into the memory cell. Using this program helps elim-
inate idle-quality changes as loads change. Finally,
the PCM incorporates a9No-Load9engine speed lim-
iter of approximately 1800 - 2000 rpm, when it rec-
ognizes that the TPS is indicating an idle signal and
IAC motor cannot maintain engine idle.
A (factory adjusted) set screw is used to mechani-
cally limit the position of the throttle body throttle
plate.Never attempt to adjust the engine idle
speed using this screw.All idle speed functions are
controlled by the IAC motor through the PCM.
KJFUEL INJECTION 14 - 35

INSTALLATION
2.4L
The intake manifold air temperature (IAT) sensor
is installed into the intake manifold plenum at the
rear end of the intake manifold.
(1) Check condition of sensor o-ring.
(2) Clean sensor mounting hole in intake manifold.
(3) Position sensor into intake manifold and rotate
clockwise until past release tab.
(4) Install electrical connector.
3.7L
The intake manifold air temperature (IAT) sensor
is installed into the left side of intake manifold ple-
num (Fig. 16).
(1) Check condition of sensor o-ring.
(2) Clean sensor mounting hole in intake manifold.
(3) Position sensor into intake manifold and rotate
clockwise until past release tab (Fig. 16).
(4) Install electrical connector.
MAP SENSOR
DESCRIPTION
2.4L
The Manifold Absolute Pressure (MAP) sensor is
mounted into the rear of the intake manifold with 1
screw.
3.7L
The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold with 2
screws.
OPERATION
The MAP sensor is used as an input to the Power-
train Control Module (PCM). It contains a silicon
based sensing unit to provide data on the manifold
vacuum that draws the air/fuel mixture into the com-
bustion chamber. The PCM requires this information
to determine injector pulse width and spark advance.
When manifold absolute pressure (MAP) equals
Barometric pressure, the pulse width will be at max-
imum.
A 5 volt reference is supplied from the PCM and
returns a voltage signal to the PCM that reflects
manifold pressure. The zero pressure reading is 0.5V
and full scale is 4.5V. For a pressure swing of 0±15
psi, the voltage changes 4.0V. To operate the sensor,
it is supplied a regulated 4.8 to 5.1 volts. Ground is
provided through the low-noise, sensor return circuit
at the PCM.The MAP sensor input is the number one contrib-
utor to fuel injector pulse width. The most important
function of the MAP sensor is to determine baromet-
ric pressure. The PCM needs to know if the vehicle is
at sea level or at a higher altitude, because the air
density changes with altitude. It will also help to cor-
rect for varying barometric pressure. Barometric
pressure and altitude have a direct inverse correla-
tion; as altitude goes up, barometric goes down. At
key-on, the PCM powers up and looks at MAP volt-
age, and based upon the voltage it sees, it knows the
current barometric pressure (relative to altitude).
Once the engine starts, the PCM looks at the voltage
again, continuously every 12 milliseconds, and com-
pares the current voltage to what it was at key-on.
The difference between current voltage and what it
was at key-on, is manifold vacuum.
During key-on (engine not running) the sensor
reads (updates) barometric pressure. A normal range
can be obtained by monitoring a known good sensor.
As the altitude increases, the air becomes thinner
(less oxygen). If a vehicle is started and driven to a
very different altitude than where it was at key-on,
the barometric pressure needs to be updated. Any
time the PCM sees Wide Open Throttle (WOT), based
upon Throttle Position Sensor (TPS) angle and RPM,
it will update barometric pressure in the MAP mem-
ory cell. With periodic updates, the PCM can make
its calculations more effectively.
The PCM uses the MAP sensor input to aid in cal-
culating the following:
²Manifold pressure
²Barometric pressure
²Engine load
²Injector pulse-width
²Spark-advance programs
²Shift-point strategies (certain automatic trans-
missions only)
²Idle speed
²Decel fuel shutoff
The MAP sensor signal is provided from a single
piezoresistive element located in the center of a dia-
phragm. The element and diaphragm are both made
of silicone. As manifold pressure changes, the dia-
phragm moves causing the element to deflect, which
stresses the silicone. When silicone is exposed to
stress, its resistance changes. As manifold vacuum
increases, the MAP sensor input voltage decreases
proportionally. The sensor also contains electronics
that condition the signal and provide temperature
compensation.
The PCM recognizes a decrease in manifold pres-
sure by monitoring a decrease in voltage from the
reading stored in the barometric pressure memory
cell. The MAP sensor is a linear sensor; meaning as
pressure changes, voltage changes proportionately.
14 - 38 FUEL INJECTIONKJ
INTAKE AIR TEMPERATURE SENSOR (Continued)

TIRES
DESCRIPTION
DESCRIPTION - TIRES
Tires are designed and engineered for each specific
vehicle. They provide the best overall performance
for normal operation. The ride and handling charac-
teristics match the vehicle's requirements. With
proper care they will give excellent reliability, trac-
tion, skid resistance, and tread life.
Driving habits have more effect on tire life than
any other factor. Careful drivers will obtain in most
cases, much greater mileage than severe use or care-
less drivers. A few of the driving habits which will
shorten the life of any tire are:
²Rapid acceleration
²Severe brake applications
²High speed driving
²Excessive speeds on turns
²Striking curbs and other obstacles
Radial-ply tires are more prone to irregular tread
wear. It is important to follow the tire rotation inter-
val,(Refer to 22 - TIRES/WHEELS - STANDARD
PROCEDURE). This will help to achieve a greater
tread life.
TIRE IDENTIFICATION
Tire type, size, aspect ratio and speed rating are
encoded in the letters and numbers imprinted on the
side wall of the tire. Refer to the chart to decipher
the tire identification code (Fig. 11).
Performance tires have a speed rating letter after
the aspect ratio number.
LETTER SPEED RATING
S 180 km/h (112 mph)
T 190 km/h (118 mph)
U 200 km/h (124 mph)
H 210 km/h (130 mph)
V 240 km/h (149 mph)
W 270 km/h (168 mph)
Y 300 km/h (186 mph)
The speed rating is not always printed on the tire
sidewall.
TIRE CHAINS
Tire snow chains may be used oncertainmodels.
Refer to the Owner's Manual for more information.
DESCRIPTION - RADIAL-PLY TIRES
Radial-ply tires improve handling, tread life and
ride quality, and decrease rolling resistance.
Radial-ply tires must always be used in sets of
four. Under no circumstances should they be used on
the front only. They may be mixed with temporary
spare tires when necessary. A maximum speed of 50
MPH is recommended while a temporary spare is in
use.
Radial-ply tires have the same load-carrying capac-
ity as other types of tires of the same size. They also
use the same recommended inflation pressures.
The use of oversized tires, either in the front or
rear of the vehicle, can cause vehicle drive train fail-
ure. This could also cause inaccurate wheel speed
signals when the vehicle is equipped with Anti-Lock
Brakes.
The use of tires from different manufactures on the
same vehicle is NOT recommended. The proper tire
pressure should be maintained on all four tires.
DESCRIPTION - SPARE TIRE &TEMPORARY
The temporary spare tire is designed for emer-
gency use only. The original tire should be repaired
or replaced at the first opportunity, then reinstalled.
Do not exceed speeds of 50 M.P.H. when using the
temporary spare tire. Refer to Owner's Manual for
complete details.
Fig. 11 Tire Identification
22 - 6 TIRES/WHEELSKJ

INSTALLATION
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION) (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
CAUTION - REFRIGERANT HOSES/LINES/TUBES
PRECAUTIONS)
The compressor may be removed and repositioned
without disconnecting the refrigerant lines or dis-
charging the refrigerant system. Discharging is not
necessary if servicing the compressor clutch or clutch
coil, the engine, the cylinder head, or the generator.
NOTE: If a replacement compressor is being
installed, be certain to check the refrigerant oil
level. (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING/REFRIGERANT OIL - STANDARD PRO-
CEDURE - REFRIGERANT OIL LEVEL) Use only
refrigerant oil of the type recommended for the
compressor in the vehicle. (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING/REFRIGERANT OIL -
DESCRIPTION)(1) Install the compressor to the mounting bracket.
Tighten the three mounting bolts to 27 N´m (20 ft.
lbs.), (2.4L gasoline and 2.5L diesel engines only).
(2) On the 3.7L gasoline engine install and tighten
the bolts in the following sequence (Fig. 5):
²The number one bolt (rear) is hand tightened
first then tightened to 55 N´m (41 ft. lbs.)
²The number three bolt is then hand tightened
and torqued to 40 N´m ( 30 ft. lbs.)
²The number two bolt is also hand tightened and
torqued to 55 N´m ( 41 ft. lbs.)
(3) Remove the tape or plugs from all of the
opened refrigerant line fittings. Install the suction
and discharge line manifold to the compressor.
Tighten the fastener to 28 N´m (250 in. lbs.).(Refer to
24 - HEATING & AIR CONDITIONING/PLUMBING/
SUCTION LINE - INSTALLATION) (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING/A/C
DISCHARGE LINE - INSTALLATION)
(4) Install the serpentine drive belt(Refer to 7 -
COOLING/ACCESSORY DRIVE/DRIVE BELTS -
INSTALLATION).
Fig. 3 A/C COMPRESSOR - 3.7L ENGINE
1 - COMPRESSOR BOLT #1
2 - COMPRESSOR BOLT #2
3 - COMPRESSOR BOLT #3
4 - A/C COMPRESSOR
5 - A/C COMPRESSOR CLUTCH AND PULLEY
6 - COMPRESSOR MOUNT
Fig. 4 A/C COMPRESSOR - 2.5L DIESEL ENGINE
1 - SUCTION LINE MOUNTING NUT
2- SUCTION LINE MOUNTING CLIP
3- SUCTION LINE
4- MOUNTING SCREW FOR SUCTION LINE
5- SUCTION LINE MOUNTING FLANG
6- MOUNTING SCREW FOR DISCHARGE LINE
7- DISCHARGE LINE MOUNTING FLANG
8- A/C PRESSURE SENSOR
9- A/C DISCHARGE LINE
10- A/C COMPRESSOR ASSEMBLY
11- A/C DISCHARGE LINE SERVICE PORT
24 - 44 PLUMBINGKJ
A/C COMPRESSOR (Continued)