2002 JEEP LIBERTY Ignition control

INSTALLATION
2.4L
The Camshaft Position Sensor (CMP) on the 2.4L
4±cylinder engine is bolted to the right-front side of
the cylinder head.Sensor position (depth) is
adjustable.
(1) Remove plastic, upper timing belt cover (timing
gear cover) (Fig. 11) by removing 3 bolts. Before
attempting to remove cover, remove electrical connec-
tor from Engine Coolant Temperature (ECT) sensor
(Fig. 11). This will prevent damage to sensor.
(2) Rotate (bump over) engine until camshaft tim-
ing gear and target wheel (tonewheel) are positioned
and aligned to face of sensor as shown in (Fig. 12).If
not positioned as shown in (Fig. 12), damage to
both sensor and target wheel will occur when
attempting to start engine. Face of sensor
MUST be behind target wheel while adjusting.
(3) Position sensor to cylinder head and install 2
sensor mounting bolts finger tight.
(4)SENSOR AIR GAP: .030ºSet air gap between
rear of target wheel and face of sensor to .030º. This
can best be accomplished using an L-shaped, wire-
type spark plug gapping gauge (Fig. 13). A piece of
.030º brass shim stock may also be used.
(5) Gently push sensor forward until it contacts
gapping gauge.Do not push hard on sensor.
Tighten 2 sensor mounting bolts. Refer to torque
specifications.CAUTION: After tightening sensor mounting bolts,
recheck air gap and adjust as necessary. Retorque
bolts.
(6) Install upper timing belt cover and 3 bolts.
(7) Connect electrical connector to ECT sensor.
(8) Connect electrical connector to CMP sensor.
Fig. 11 UPPER TIMING BELT COVER/BOLTS-2.4L
1 - UPPER TIMING BELT COVER
2 - ELECTRICAL CONNECTOR (ECT)
3 - MOUNTING BOLTS (3)
Fig. 12 CMP FACE AT TARGET WHEEL-2.4L
1 - CAMSHAFT DRIVE GEAR
2 - TARGETWHEEL (TONEWHEEL)
3 - FACE OF CMP SENSOR
4 - CUTOUT (NOTCH)
Fig. 13 CMP ADJUSTMENT - 2.4L
1 - FACE OF SENSOR
2 - WIRE GAPPING TOOL
8I - 8 IGNITION CONTROLKJ
CAMSHAFT POSITION SENSOR (Continued)

3.7L
The Camshaft Position Sensor (CMP) on the 3.7L
V-6 engine is bolted to the front/top of the right cyl-
inder head.
(1) Clean out machined hole in cylinder head.
(2) Apply a small amount of engine oil to sensor
o-ring.
(3) Install sensor into cylinder head with a slight
rocking and twisting action.
CAUTION: Before tightening sensor mounting bolt,
be sure sensor is completely flush to cylinder head.
If sensor is not flush, damage to sensor mounting
tang may result.
(4) Install mounting bolt and tighten. Refer to
torque specifications.
(5) Connect electrical connector to sensor.
IGNITION COIL
DESCRIPTION
2.4L
The coil assembly consists of 2 different coils
molded together. The assembly is mounted to the top
of the engine (Fig. 14).
3.7L
The 3.7L V-6 engine uses 6 dedicated, and individ-
ually fired coil for each spark plug (Fig. 15). Each
coil is mounted directly into the cylinder head and
onto the top of each spark plug (Fig. 16).
OPERATION
2.4L
The coil fires two spark plugs simultaneously. One
plug is under compression, the other plug fires on the
exhaust stroke (lost spark). Coil number one fires
Fig. 14 IGNITION COIL - 2.4L
1 - IGNITION COIL
2 - MOUNTING BOLTS (4)
Fig. 15 IGNITION COIL - 3.7L
1 - O-RING
2 - IGNITION COIL
3 - ELECTRICAL CONNECTOR
Fig. 16 IGNITION COIL LOCATION - 3.7L
1 - IGNITION COIL
2 - COIL MOUNTING NUT
KJIGNITION CONTROL 8I - 9
CAMSHAFT POSITION SENSOR (Continued)

cylinders 1 and 4, and coil number two fires cylinders
2 and 3.
The Auto Shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing the coil(s). The
PCM will de-energize the ASD relay if it does not
receive the crankshaft position sensor and camshaft
position sensor inputs.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to set
the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
Spark plug cables (secondary wires or cables) are
used with the 2.4L engine.
3.7L
Battery voltage is supplied to the 6 ignition coils
from the ASD relay. The Powertrain Control Module
(PCM) opens and closes each ignition coil ground cir-
cuit at a determined time for ignition coil operation.
Base ignition timing is not adjustable.By con-
trolling the coil ground circuit, the PCM is able to set
the base timing and adjust the ignition timing
advance. This is done to meet changing engine oper-
ating conditions.
The ignition coil is not oil filled. The windings are
embedded in an epoxy compound. This provides heat
and vibration resistance that allows the ignition coil
to be mounted on the engine.
Because of coil design, spark plug cables (second-
ary cables) are not used with the 3.7L engine.
REMOVAL
2.4L
(1) Disconnect electrical connector at rear of coil.
(2) Remove all secondary cables from coil.
(3) Remove 4 coil mounting bolts (Fig. 17).
(4) Remove coil from vehicle.
3.7L
An individual ignition coil is used for each spark
plug (Fig. 19). The coil fits into machined holes in the
cylinder head. A mounting stud/nut secures each coil
to the top of the intake manifold (Fig. 18). The bot-
tom of the coil is equipped with a rubber boot to seal
the spark plug to the coil. Inside each rubber boot is
a spring. The spring is used for a mechanical contact
between the coil and the top of the spark plug. These
rubber boots and springs are a permanent part of the
coil and are not serviced separately. An o-ring (Fig.19) is used to seal the coil at the opening into the cyl-
inder head.
(1) Depending on which coil is being removed, the
throttle body air intake tube or intake box may need
to be removed to gain access to coil.
(2) Disconnect electrical connector from coil by
pushing downward on release lock on top of connec-
tor and pull connector from coil.
(3) Clean area at base of coil with compressed air
before removal.
(4) Remove coil mounting nut from mounting stud
(Fig. 18).
(5) Carefully pull up coil from cylinder head open-
ing with a slight twisting action.
(6) Remove coil from vehicle.
INSTALLATION
2.4L
(1) Position coil to engine.
(2) Install 4 mounting bolts. Refer to torque speci-
fications.
(3) Install secondary cables.
(4) Install electrical connector at rear of coil.
(5) Install air cleaner tube and housing.
3.7L
(1) Using compressed air, blow out any dirt or con-
taminants from around top of spark plug.
(2) Check condition of coil o-ring and replace as
necessary. To aid in coil installation, apply silicone to
coil o-ring.
Fig. 17 IGNITION COIL - 2.4L
1 - IGNITION COIL
2 - MOUNTING BOLTS (4)
8I - 10 IGNITION CONTROLKJ
IGNITION COIL (Continued)

(3) Position ignition coil into cylinder head opening
and push onto spark plug. Do this while guiding coil
base over mounting stud.
(4) Install coil mounting stud nut. Refer to torque
specifications.(5) Connect electrical connector to coil by snapping
into position.
(6) If necessary, install throttle body air tube or
box.
KNOCK SENSOR
DESCRIPTION
The 2 knock sensors are bolted into the cylinder
block under the intake manifold. The sensors are
used only with the 3.7L engine.
OPERATION
Two knock sensors are used on the 3.7L V-6
engine; one for each cylinder bank. When the knock
sensor detects a knock in one of the cylinders on the
corresponding bank, it sends an input signal to the
Powertrain Control Module (PCM). In response, the
PCM retards ignition timing for all cylinders by a
scheduled amount.
Knock sensors contain a piezoelectric material
which constantly vibrates and sends an input voltage
(signal) to the PCM while the engine operates. As the
intensity of the crystal's vibration increases, the
knock sensor output voltage also increases.
The voltage signal produced by the knock sensor
increases with the amplitude of vibration. The PCM
receives the knock sensor voltage signal as an input.
If the signal rises above a predetermined level, the
PCM will store that value in memory and retard
ignition timing to reduce engine knock. If the knock
sensor voltage exceeds a preset value, the PCM
retards ignition timing for all cylinders. It is not a
selective cylinder retard.
The PCM ignores knock sensor input during engine
idle conditions. Once the engine speed exceeds a
specified value, knock retard is allowed.
Knock retard uses its own short term and long
term memory program.
Long term memory stores previous detonation
information in its battery-backed RAM. The maxi-
mum authority that long term memory has over tim-
ing retard can be calibrated.
Short term memory is allowed to retard timing up
to a preset amount under all operating conditions (as
long as rpm is above the minimum rpm) except at
Wide Open Throttle (WOT). The PCM, using short
term memory, can respond quickly to retard timing
when engine knock is detected. Short term memory
is lost any time the ignition key is turned off.
Fig. 18 IGNITION COIL LOCATION - 3.7L
1 - IGNITION COIL
2 - COIL MOUNTING NUT
Fig. 19 IGNITION COIL - 3.7L
1 - O-RING
2 - IGNITION COIL
3 - ELECTRICAL CONNECTOR
KJIGNITION CONTROL 8I - 11
IGNITION COIL (Continued)

NOTE: Over or under tightening the sensor mount-
ing bolts will affect knock sensor performance, pos-
sibly causing improper spark control. Always use
the specified torque when installing the knock sen-
sors.
REMOVAL
The 2 knock sensors are bolted into the cylinder
block under the intake manifold (Fig. 20).
NOTE: The left sensor is identified by an identifica-
tion tag (LEFT). It is also identified by a larger bolt
head. The Powertrain Control Module (PCM) must
have and know the correct sensor left/right posi-
tions. Do not mix the sensor locations.
(1) Disconnect knock sensor dual pigtail harness
from engine wiring harness. this connection is made
near rear of left valve cover (Fig. 20).
(2) Remove intake manifold. Refer to Engine sec-
tion.
(3) Remove sensor mounting bolts (Fig. 20). Note
foam strip on bolt threads. This foam is used only to
retain the bolts to sensors for plant assembly. It is
not used as a sealant. Do not apply any adhesive,
sealant or thread locking compound to these bolts.
(4) Remove sensors from engine.
INSTALLATION
NOTE: The left sensor is identified by an identifica-
tion tag (LEFT). It is also identified by a larger bolt
head. The Powertrain Control Module (PCM) must
have and know the correct sensor left/right posi-
tions. Do not mix the sensor locations.
(1) Thoroughly clean knock sensor mounting holes.
(2) Install sensors into cylinder block.
NOTE: Over or under tightening the sensor mount-
ing bolts will affect knock sensor performance, pos-
sibly causing improper spark control. Always use
the specified torque when installing the knock sen-
sors. The torque for the knock senor bolt is rela-
tively light for an 8mm bolt.
NOTE: Note foam strip on bolt threads. This foam is
used only to retain the bolts to sensors for plant
assembly. It is not used as a sealant. Do not apply
any adhesive, sealant or thread locking compound
to these bolts.
(3) Install and tighten mounting bolts. Refer to
torque specification.
(4) Install intake manifold. Refer to Engine sec-
tion.
(5) Connect knock sensor wiring harness to engine
harness at rear of intake manifold.
SPARK PLUG
DESCRIPTION
Resistor type spark plugs are used.
Spark plug resistance values range from 6,000 to
20,000 ohms (when checked with at least a 1000 volt
spark plug tester).Do not use an ohmmeter to
check the resistance values of the spark plugs.
Inaccurate readings will result.
OPERATION
To prevent possible pre-ignition and/or mechanical
engine damage, the correct type/heat range/number
spark plug must be used.
Always use the recommended torque when tighten-
ing spark plugs. This is especially true when plugs
are equipped with tapered seats. Incorrect torque can
distort the spark plug and change plug gap. It can
also pull the plug threads and do possible damage to
both the spark plug and the cylinder head.
Remove the spark plugs and examine them for
burned electrodes and fouled, cracked or broken por-
celain insulators. Keep plugs arranged in the order
in which they were removed from the engine. A sin-
Fig. 20 KNOCK SENSOR LOCATION
1 - KNOCK SENSORS (2)
2 - MOUNTING BOLTS
8I - 12 IGNITION CONTROLKJ
KNOCK SENSOR (Continued)

gle plug displaying an abnormal condition indicates
that a problem exists in the corresponding cylinder.
Replace spark plugs at the intervals recommended in
the Lubrication and Maintenance section.
Spark plugs that have low mileage may be cleaned
and reused if not otherwise defective, carbon or oil
fouled. Also refer to Spark Plug Conditions.
CAUTION: Never use a motorized wire wheel brush
to clean the spark plugs. Metallic deposits will
remain on the spark plug insulator and will cause
plug misfire.
DIAGNOSIS AND TESTING - SPARK PLUG
CONDITIONS
NORMAL OPERATING
The few deposits present on the spark plug will
probably be light tan or slightly gray in color. This is
evident with most grades of commercial gasoline
(Fig. 21). There will not be evidence of electrode
burning. Gap growth will not average more than
approximately 0.025 mm (.001 in) per 3200 km (2000
miles) of operation. Spark plugs that have normal
wear can usually be cleaned, have the electrodes
filed, have the gap set and then be installed.
Some fuel refiners in several areas of the United
States have introduced a manganese additive (MMT)
for unleaded fuel. During combustion, fuel with MMT
causes the entire tip of the spark plug to be coated
with a rust colored deposit. This rust color can be
misdiagnosed as being caused by coolant in the com-bustion chamber. Spark plug performance may be
affected by MMT deposits.
COLD FOULING/CARBON FOULING
Cold fouling is sometimes referred to as carbon
fouling. The deposits that cause cold fouling are basi-
cally carbon (Fig. 21). A dry, black deposit on one or
two plugs in a set may be caused by sticking valves
or defective spark plug cables. Cold (carbon) fouling
of the entire set of spark plugs may be caused by a
clogged air cleaner element or repeated short operat-
ing times (short trips).
WET FOULING OR GAS FOULING
A spark plug coated with excessive wet fuel or oil
is wet fouled. In older engines, worn piston rings,
leaking valve guide seals or excessive cylinder wear
can cause wet fouling. In new or recently overhauled
engines, wet fouling may occur before break-in (nor-
mal oil control) is achieved. This condition can usu-
ally be resolved by cleaning and reinstalling the
fouled plugs.
OIL OR ASH ENCRUSTED
If one or more spark plugs are oil or oil ash
encrusted (Fig. 22), evaluate engine condition for the
cause of oil entry into that particular combustion
chamber.
ELECTRODE GAP BRIDGING
Electrode gap bridging may be traced to loose
deposits in the combustion chamber. These deposits
accumulate on the spark plugs during continuous
stop-and-go driving. When the engine is suddenly
Fig. 21 Normal Operation and Cold (Carbon) Fouling
1 - NORMAL
2 - DRY BLACK DEPOSITS
3 - COLD (CARBON) FOULING
Fig. 22 Oil or Ash Encrusted
KJIGNITION CONTROL 8I - 13
SPARK PLUG (Continued)

subjected to a high torque load, deposits partially liq-
uefy and bridge the gap between electrodes (Fig. 23).
This short circuits the electrodes. Spark plugs with
electrode gap bridging can be cleaned using standard
procedures.
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 24). They may appear to be harmful, but
this is a normal condition caused by chemical addi-
tives in certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice that accumula-
tion on the ground electrode and shell area may be
heavy, but the deposits are easily removed. Spark
plugs with scavenger deposits can be considered nor-
mal in condition and can be cleaned using standard
procedures.
CHIPPED ELECTRODE INSULATOR
A chipped electrode insulator usually results from
bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation can also separate the insulator
from the center electrode (Fig. 25). Spark plugs with
this condition must be replaced.
PREIGNITION DAMAGE
Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec-
trode dissolves first and the ground electrode dis-
solves somewhat latter (Fig. 26). Insulators appear
relatively deposit free. Determine if the spark plug
has the correct heat range rating for the engine.
Determine if ignition timing is over advanced or if
other operating conditions are causing engine over-heating. (The heat range rating refers to the operat-
ing temperature of a particular type spark plug.
Spark plugs are designed to operate within specific
temperature ranges. This depends upon the thick-
ness and length of the center electrodes porcelain
insulator.)
SPARK PLUG OVERHEATING
Overheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.
27). The increase in electrode gap will be consider-
ably in excess of 0.001 inch per 2000 miles of opera-
tion. This suggests that a plug with a cooler heat
range rating should be used. Over advanced ignition
timing, detonation and cooling system malfunctions
can also cause spark plug overheating.
Fig. 23 Electrode Gap Bridging
1 - GROUND ELECTRODE
2 - DEPOSITS
3 - CENTER ELECTRODE
Fig. 24 Scavenger Deposits
1 - GROUND ELECTRODE COVERED WITH WHITE OR
YELLOW DEPOSITS
2 - CENTER ELECTRODE
Fig. 25 Chipped Electrode Insulator
1 - GROUND ELECTRODE
2 - CENTER ELECTRODE
3 - CHIPPED INSULATOR
8I - 14 IGNITION CONTROLKJ
SPARK PLUG (Continued)

REMOVAL
2.4L
If spark plug for #2 or #3 cylinder is being
removed, throttle body must be removed. Refer to
Throttle Body Removal.
(1) Remove air cleaner tube and housing.
(2) Twist secondary cable at cylinder head to break
loose at spark plug. Remove cable from plug.
(3) Prior to removing spark plug, spray com-
pressed air into cylinder head opening. This will help
prevent foreign material from entering combustion
chamber.
(4) Remove spark plug from cylinder head using a
quality socket with a rubber or foam insert.
(5) Inspect spark plug condition. Refer to Spark
Plug Conditions.
3.7L
Each individual spark plug is located under each
ignition coil. Each individual ignition coil must be
removed to gain access to each spark plug. Refer to
Ignition Coil Removal/Installation.
(1) Prior to removing ignition coil, spray com-
pressed air around coil base at cylinder head.
(2) Prior to removing spark plug, spray com-
pressed air into cylinder head opening. This will help
prevent foreign material from entering combustion
chamber.
(3) Remove spark plug from cylinder head using a
quality socket with a rubber or foam insert. Also
check condition of ignition coil o-ring and replace as
necessary.
(4) Inspect spark plug condition. Refer to Spark
Plug Conditions.
CLEANING SPARK PLUGS
The plugs may be cleaned using commercially
available spark plug cleaning equipment. After clean-
ing, file the center electrode flat with a small point
file or jewelers file before adjusting gap.
CAUTION: Never use a motorized wire wheel brush
to clean the spark plugs. Metallic deposits will
remain on the spark plug insulator and will cause
plug misfire.
INSTALLATION
2.4L
CAUTION: Spark plug tightening on the 2.4L is
torque critical. The plugs are equipped with tapered
seats. Do not exceed 15 ft. lbs. torque.
Special care should be taken when installing spark
plugs into the cylinder head spark plug wells. Be
sure the plugs do not drop into the plug wells as elec-
trodes can be damaged.
Always tighten spark plugs to the specified torque.
Over tightening can cause distortion resulting in a
change in the spark plug gap or a cracked porcelain
insulator.
(1) Start the spark plug into the cylinder head by
hand to avoid cross threading.
(2) Tighten spark plugs. Refer to torque specifica-
tions.
(3) Install throttle body. Refer to Throttle Body
Installation.
(4) Install air cleaner tube and housing.
3.7L
Special care should be taken when installing spark
plugs into the cylinder head spark plug wells. Be
Fig. 26 Preignition Damage
1 - GROUND ELECTRODE STARTING TO DISSOLVE
2 - CENTER ELECTRODE DISSOLVED
Fig. 27 Spark Plug Overheating
1 - BLISTERED WHITE OR GRAY COLORED INSULATOR
KJIGNITION CONTROL 8I - 15
SPARK PLUG (Continued)