IGNITION CONTROL TABLE OF CONTENTS page page IGNITION CONTROL DESCRIPTION .......................... 1 OPERATION ............................ 1 SPECIFICATIONS SPECIFICATIONS - IGNITION TIMING ....... 2 ENGINE FIRING ORDER - 2.4L 4-CYLINDER .2 ENGINE FIRING ORDER - 4.0L 6-CYLINDER ENGINE .............................. 2 IGNITION COIL RESISTANCE - 2.4L ........ 2 IGNITION COIL RESISTANCE - 4.0L ENGINE .3 SPARK PLUGS ........................ 3 SPECIFICATIONS - SPARK PLUG CABLE RESISTANCE ......................... 3 SPECIFICATIONS - TORQUE - IGNITION SYSTEM ............................. 3 AUTO SHUT DOWN RELAY DESCRIPTION - PCM OUTPUT ............. 4 OPERATION OPERATION - ASD SENSE - PCM INPUT .... 4 OPERATION - PCM OUTPUT ............. 4 DIAGNOSIS AND TESTING - ASD AND FUEL PUMP RELAYS ........................ 4 REMOVAL ............................. 5 INSTALLATION .......................... 5 CAMSHAFT POSITION SENSOR - 2.4L DESCRIPTION - 2.4L ..................... 5 OPERATION - 2.4L ....................... 5 REMOVAL - 2.4L ......................... 6 INSTALLATION - 2.4L ..................... 6 CAMSHAFT POSITION SENSOR - 4.0L DESCRIPTION - 4.0L ..................... 7 OPERATION - 4.0L ....................... 8 REMOVAL - 4.0L ......................... 8 INSTALLATION - 4.0L .................... 10 COIL RAIL - 4.0L DESCRIPTION - 4.0L .................... 10 OPERATION - 4.0L ...................... 11 REMOVAL - 4.0L ........................ 11 INSTALLATION - 4.0L .................... 12 IGNITION COIL - 2.4L DESCRIPTION - 2.4L .................... 13 OPERATION - 2.4L ...................... 13 REMOVAL - 2.4L ........................ 13 INSTALLATION - 2.4L .................... 13 SPARK PLUG DESCRIPTION ......................... 13 OPERATION ........................... 13 DIAGNOSIS AND TESTING - SPARK PLUG CONDITIONS ......................... 14 REMOVAL ............................. 16 CLEANING CLEANING SPARK PLUGS .............. 16 INSTALLATION ......................... 17 SPARK PLUG CABLE DESCRIPTION ......................... 17 OPERATION ........................... 17 DIAGNOSIS AND TESTING ................ 17 REMOVAL - 2.4L ........................ 18 INSTALLATION ......................... 18 IGNITION CONTROL DESCRIPTION The ignition systems used on both the 2.4L 4–cyl- inder and 4.0L 6–cylinder engines are a distributor- less type. The ignition system consists of: • Spark Plugs • Spark Plug Cables (secondary wires) • Ignition Coil(s) • Powertrain Control Module (PCM) • Crankshaft Position Sensor • Camshaft Position Sensor • The MAP, TPS, IAC and ECT also have an effect on the control of the ignition system. OPERATION 2.4L A common ignition coil divided into 2 halves is used. Secondary, high-tension spark plug cables are also used. One half of the coil fires two spark plugs simultaneously (one plug is the cylinder under com- pression, and the other plug is the cylinder on the exhaust stroke). Coil half number one fires cylinders 1 and 4. Coil half number two fires cylinders 2 and 3. The PCM determines which of the coils to charge and fire at the correct time. The Auto Shutdown (ASD) relay provides battery voltage to the ignition coil. The PCM provides a ground contact (circuit) for energizing the coil. When the PCM breaks the contact, the energy in the coil TJ IGNITION CONTROL 8I - 1
DESCRIPTIONThe ignition systems used on both the 2.4L 4–cyl-
inder and 4.0L 6–cylinder engines are a distributor-less type.
The ignition system consists of:• Spark Plugs• Spark Plug Cables (secondary wires)• Ignition Coil(s)• Powertrain Control Module (PCM)• Crankshaft Position Sensor• Camshaft Position Sensor• The MAP, TPS, IAC and ECT also have an effect
on the control of the ignition system.
OPERATION
2.4LA common ignition coil divided into 2 halves is
used. Secondary, high-tension spark plug cables arealso used. One half of the coil fires two spark plugssimultaneously (one plug is the cylinder under com-pression, and the other plug is the cylinder on theexhaust stroke). Coil half number one fires cylinders1 and 4. Coil half number two fires cylinders 2 and 3.The PCM determines which of the coils to charge andfire at the correct time.
The Auto Shutdown (ASD) relay provides batteryvoltage to the ignition coil. The PCM provides aground contact (circuit) for energizing the coil. Whenthe PCM breaks the contact, the energy in the coil
TJ IGNITION CONTROL 8I - 1
primary transfers to the secondary causing a spark.The PCM will de-energize the ASD relay if it doesnot receive inputs from either the crankshaft or cam-shaft position sensors.
A distributor is not used with the 2.4L engine.
4.0LThe 4.0L 6-cylinder engine uses a one-piece coil
rail containing three independent coils. Although cyl-inder firing order is the same as 4.0L engines of pre-vious years, spark plug firing is not. The 3 coils dual-fire the spark plugs on cylinders 1-6, 2-5 and/or 3-4.When one cylinder is being fired (on compressionstroke), the spark to the opposite cylinder is beingwasted (on exhaust stroke). The one-piece coil boltsdirectly to the cylinder head. Rubber boots seal thesecondary terminal ends of the coils to the top of all6 spark plugs. One electrical connector (located atthe rear end of the coil rail) is used for all three coils.
Because of coil design, spark plug cables (second-ary cables) are not used. A distributor is not usedwith the 4.0L engine.
The ignition system is controlled by the PowertrainControl Module (PCM).
SPECIFICATIONS
SPECIFICATIONS - IGNITION TIMINGIgnition timing is not adjustable on anyengine.
relay is located in the Power Distribution Center(PDC). Refer to label on PDC cover for relay location.
OPERATION
OPERATION - ASD SENSE - PCM INPUTA 12 volt signal at this input indicates to the PCM
that the ASD has been activated. The relay is used toconnect the oxygen sensor heater element, ignitioncoil and fuel injectors to 12 volt + power supply.
This input is used only to sense that the ASD relayis energized. If the Powertrain Control Module(PCM) does not see 12 volts at this input when theASD should be activated, it will set a DiagnosticTrouble Code (DTC).
to the fuel injectors and ignition coil(s). With certainemissions packages it also supplies 12–volts to theoxygen sensor heating elements.
The ground circuit for the coil within the ASDrelay is controlled by the Powertrain Control Module(PCM). The PCM operates the ASD relay by switch-ing its ground circuit on and off.
The ASD relay will be shut–down, meaning the12–volt power supply to the ASD relay will be de-ac-tivated by the PCM if:
• the ignition key is left in the ON position. Thisis if the engine has not been running for approxi-mately 1.8 seconds.
• there is a crankshaft position sensor signal tothe PCM that is lower than pre-determined values.
DIAGNOSIS AND TESTING - ASD AND FUELPUMP RELAYS
The following description of operation andtests apply only to the Automatic Shutdown(ASD) and fuel pump relays. The terminals on thebottom of each relay are numbered. Two differenttypes of relays may be used, (Fig. 1) or (Fig. 2).
• Terminal number 30 is connected to battery volt-age. For both the ASD and fuel pump relays, termi-nal 30 is connected to battery voltage at all times.
• The PCM grounds the coil side of the relaythrough terminal number 85.
• Terminal number 86 supplies voltage to the coilside of the relay.
• When the PCM de-energizes the ASD and fuelpump relays, terminal number 87A connects to termi-nal 30. This is the Off position. In the off position,
voltage is not supplied to the rest of the circuit. Ter-minal 87A is the center terminal on the relay.
• When the PCM energizes the ASD and fuelpump relays, terminal 87 connects to terminal 30.This is the On position. Terminal 87 supplies voltageto the rest of the circuit.
The following procedure applies to the ASD andfuel pump relays.
(1) Remove relay from connector before testing.(2) With the relay removed from the vehicle, use
an ohmmeter to check the resistance between termi-nals 85 and 86. The resistance should be 75 ohms +/-5 ohms.
(3) Connect the ohmmeter between terminals 30and 87A. The ohmmeter should show continuitybetween terminals 30 and 87A.
Fig. 1 ASD and Fuel Pump Relay Terminals—Type 1
Fig. 2 ASD and Fuel Pump Relay Terminals—Type 2TERMINAL LEGEND
NUMBER IDENTIFICATION
30 COMMON FEED85 COIL GROUND86 COIL BATTERY87 NORMALLY OPEN
87A NORMALLY CLOSED
8I - 4 IGNITION CONTROL TJ
(4) Connect the ohmmeter between terminals 87and 30. The ohmmeter should not show continuity atthis time.
(5) Connect one end of a jumper wire (16 gauge orsmaller) to relay terminal 85. Connect the other endof the jumper wire to the ground side of a 12 voltpower source.
(6) Connect one end of another jumper wire (16gauge or smaller) to the power side of the 12 voltpower source. Do not attach the other end of thejumper wire to the relay at this time.
WARNING: DO NOT ALLOW OHMMETER TO CON-TACT TERMINALS 85 OR 86 DURING THIS TEST.DAMAGE TO OHMMETER MAY RESULT.
(7) Attach the other end of the jumper wire torelay terminal 86. This activates the relay. The ohm-meter should now show continuity between relay ter-minals 87 and 30. The ohmmeter should not showcontinuity between relay terminals 87A and 30.
(8) Disconnect jumper wires.(9) Replace the relay if it did not pass the continu-
ity and resistance tests. If the relay passed the tests,it operates properly. Check the remainder of the ASDand fuel pump relay circuits. Refer to 8, Wiring Dia-grams.
REMOVALThe ASD relay is located in the Power Distribution
Center (PDC) (Fig. 3). Refer to label on PDC coverfor relay location.
(1) Remove PDC cover.(2) Remove relay from PDC.(3) Check condition of relay terminals and PDC
connector terminals for damage or corrosion. Repairif necessary before installing relay.
(4) Check for pin height (pin height should be thesame for all terminals within the PDC connector).Repair if necessary before installing relay.
INSTALLATIONThe ASD relay is located in the Power Distribution
Center (PDC) (Fig. 3). Refer to label on PDC coverfor relay location.
(1) Install relay to PDC.(2) Install cover to PDC.
CAMSHAFT POSITIONSENSOR - 2.4L
DESCRIPTION - 2.4LThe Camshaft Position Sensor (CMP) on the 2.4L
4–cylinder engine is bolted to the right-front side ofthe cylinder head (Fig. 4).
OPERATION - 2.4LThe Camshaft Position Sensor (CMP) sensor con-
tains a hall effect device referred to as a sync signalgenerator. A rotating target wheel (tonewheel) for theCMP is located behind the exhaust valve-camshaftdrive gear (Fig. 5). The target wheel is equipped witha cutout (notch) around 180 degrees of the wheel.The CMP detects this cutout every 180 degrees ofcamshaft gear rotation. Its signal is used in conjunc-tion with the Crankshaft Position Sensor (CKP) todifferentiate between fuel injection and spark events.It is also used to synchronize the fuel injectors withtheir respective cylinders.
Fig. 3 Power Distribution Center (PDC)1 - BATTERY2 - POWER DISTRIBUTION CENTER (PDC)
When the leading edge of the target wheel cutoutenters the tip of the CMP, the interruption of mag-netic field causes the voltage to switch high, result-ing in a sync signal of approximately 5 volts.
When the trailing edge of the target wheel cutoutleaves the tip of the CMP, the change of the magneticfield causes the sync signal voltage to switch low to 0volts.
REMOVAL - 2.4LThe Camshaft Position Sensor (CMP) on the 2.4L
4–cylinder engine is bolted to the right-front side ofthe cylinder head (Fig. 6). Sensor position (depth) isadjustable.
(1) Disconnect electrical connector at CMP sensor.(2) Remove 2 sensor mounting bolts.(3) Remove sensor from cylinder head by sliding
towards rear of engine.
INSTALLATION - 2.4LThe Camshaft Position Sensor (CMP) on the 2.4L
4–cylinder engine is bolted to the right-front side ofthe cylinder head. Sensor position (depth) isadjustable.
(1) Remove plastic, upper timing belt cover (timinggear cover) (Fig. 7) by removing 3 bolts. Beforeattempting to remove cover, remove electrical connec-tor from Engine Coolant Temperature (ECT) sensor(Fig. 7). This will prevent damage to sensor.
(2) Rotate (bump over) engine until camshaft tim-ing gear and target wheel (tonewheel) are positionedand aligned to face of sensor as shown in (Fig. 8). Ifnot positioned as shown in (Fig. 8), damage toboth sensor and target wheel will occur whenattempting to start engine. Face of sensorMUST be behind target wheel while adjusting.
(3) Position sensor to cylinder head and install 2sensor mounting bolts finger tight.
(4) SENSOR AIR GAP: .030” Set air gap betweenrear of target wheel and face of sensor to .030”. Thiscan best be accomplished using an L-shaped, wire-type spark plug gapping gauge (Fig. 9). A piece of.030” brass shim stock may also be used.
(5) Gently push sensor forward until it contactsgapping gauge. Do not push hard on sensor.Tighten 2 sensor mounting bolts. Refer to torquespecifications.
CAUTION: After tightening sensor mounting bolts,recheck air gap and adjust as necessary. Retorquebolts.
(6) Install upper timing belt cover and 3 bolts.(7) Connect electrical connector to ECT sensor.(8) Connect electrical connector to CMP sensor.
Fig. 5 CMP FACE AT TARGET WHEEL-2.4L1 - CAMSHAFT DRIVE GEAR2 - TARGETWHEEL (TONEWHEEL)3 - FACE OF CMP SENSOR4 - CUTOUT (NOTCH)
DESCRIPTION - 4.0LThe Camshaft Position Sensor (CMP) on the 4.0L
6–cylinder engine is bolted to the top of the oil pumpdrive shaft assembly (Fig. 10). The sensor and driveshaft assembly is located on the right side of theengine near the oil filter (Fig. 11).
Fig. 7 UPPER TIMING BELT COVER/BOLTS-2.4L1 - UPPER TIMING BELT COVER2 - ELECTRICAL CONNECTOR (ECT)3 - MOUNTING BOLTS (3)
Fig. 8 CMP FACE AT TARGET WHEEL-2.4L1 - CAMSHAFT DRIVE GEAR2 - TARGETWHEEL (TONEWHEEL)3 - FACE OF CMP SENSOR4 - CUTOUT (NOTCH)
Fig. 9 CMP ADJUSTMENT - 2.4L1 - FACE OF SENSOR2 - WIRE GAPPING TOOL
OPERATION - 4.0LThe CMP sensor contains a hall effect device called
a sync signal generator to generate a fuel sync sig-nal. This sync signal generator detects a rotatingpulse ring (shutter) on the oil pump drive shaft (Fig.10). The pulse ring rotates 180 degrees through thesync signal generator. Its signal is used in conjunc-tion with the crankshaft position sensor to differenti-ate between fuel injection and spark events. It is alsoused to synchronize the fuel injectors with theirrespective cylinders.
When the leading edge of the pulse ring (shutter)enters the sync signal generator, the following occurs:The interruption of magnetic field causes the voltageto switch high resulting in a sync signal of approxi-mately 5 volts.
When the trailing edge of the pulse ring (shutter)leaves the sync signal generator, the following occurs:The change of the magnetic field causes the sync sig-nal voltage to switch low to 0 volts.
REMOVAL - 4.0LThe Camshaft Position Sensor (CMP) on the 4.0L
6–cylinder engine is bolted to the top of the oil pumpdrive shaft assembly (Fig. 12). The sensor and driveshaft assembly is located on the right side of theengine near the oil filter (Fig. 13).
The rotational position of oil pump drive deter-mines fuel synchronization only. It does not deter-mine ignition timing.
NOTE: Do not attempt to rotate the oil pump driveto modify ignition timing.
Two different procedures are used for removaland installation. The first procedure will detailremoval and installation of the sensor only. The sec-ond procedure will detail removal and installation ofthe sensor and oil pump drive shaft assembly. Thesecond procedure is to be used if the engine has beendisassembled.
An internal oil seal is used in the drive shaft hous-ing that prevents engine oil at the bottom of the sen-sor. The seal is not serviceable.
(3) Remove sensor from oil pump drive.(4) Before proceeding to next step, mark and note
rotational position of oil pump drive in relationshipto engine block. After installation, the CMP sensorshould face rear of engine 0°.
(5) Remove hold-down bolt and clamp (Fig. 13).(6) While pulling assembly from engine, note direc-
tion and position of pulse ring (Fig. 12). Afterremoval, look down into top of oil pump and notedirection and position of slot at top of oil pump gear.
(7) Remove and discard old oil pump drive-to-en-gine block gasket.
Fig. 14 CMP Pulse Ring Alignment - 4.0L Engine1 - PULSE RING (SHUTTER)2 - TOOTHPICK3 - SENSOR BASE (OIL PUMP DRIVESHAFT ASSEMBLY)
Fig. 15 Align Timing Marks - 4.0L Engine1 - CRANKSHAFT VIBRATION DAMPER TIMING MARK
TJ IGNITION CONTROL 8I - 9
CAMSHAFT POSITION SENSOR - 4.0L (Continued)
INSTALLATION - 4.0L
SENSOR ONLY - 4.0LThe Camshaft Position Sensor (CMP) on the 4.0L
6–cylinder engine is bolted to the top of the oil pumpdrive shaft assembly (Fig. 12). The sensor and driveshaft assembly is located on the right side of theengine near the oil filter (Fig. 13).
(1) Install sensor to oil pump drive.(2) Install 2 sensor mounting bolts and tighten to
2 N·m (15 in. lbs.) torque.(3) Connect electrical connector to CMP sensor.
OIL PUMP DRIVE AND SENSOR - 4.0L(1) Clean oil pump drive mounting hole area of
engine block.(2) Install new oil pump drive-to-engine block gas-
ket.(3) Temporarily install a toothpick or similar tool
through access hole at side of oil pump drive housing.Align toothpick into mating hole on pulse ring (Fig.14).
(4) Install oil pump drive into engine while align-ing into slot on oil pump. Rotate oil pump drive backto its original position and install hold-down clampand bolt. Finger tighten bolt. Do not do a final tight-ening of bolt at this time.
(5) If engine crankshaft or camshaft has beenrotated, such as during engine tear-down, CMP sen-sor relationship must be reestablished.
(b) Remove cylinder number 1 spark plug.(c) Hold a finger over the open spark plug hole.
Rotate engine at vibration dampener bolt untilcompression (pressure) is felt.
(d) Slowly continue to rotate engine. Do thisuntil timing index mark on vibration damper pul-ley aligns with top dead center (TDC) mark (0degree) on timing degree scale (Fig. 15). Alwaysrotate engine in direction of normal rotation. Donot rotate engine backward to align timing marks.
(e) Install oil pump drive into engine whilealigning into slot on oil pump. If pump drive willnot drop down flush to engine block, the oil pumpslot is not aligned. Remove oil pump drive andalign slot in oil pump to shaft at bottom of drive.Install into engine. Rotate oil pump drive back toits original position and install hold-down clampand bolt. Finger tighten bolt. Do not do a finaltightening of bolt at this time.
(f) Remove toothpick from housing.(6) Install sensor to oil pump drive. After installa-
tion, the CMP sensor should face rear of engine 0°.(7) Install 2 sensor mounting bolts and tighten to
2 N·m (15 in. lbs.) torque.
(8) Connect electrical connector to CMP sensor.(9) If removed, install spark plug and ignition coil
rail.To verify correct rotational position of oil pump
drive, the DRB scan tool must be used.
WARNING: WHEN PERFORMING THE FOLLOWINGTEST, THE ENGINE WILL BE RUNNING. BE CARE-FUL NOT TO STAND IN LINE WITH THE FANBLADES OR FAN BELT. DO NOT WEAR LOOSECLOTHING.
(10) Connect DRB scan tool to data link connector.The data link connector is located in passenger com-partment, below and to left of steering column.
(11) Gain access to SET SYNC screen on DRB.(12) Follow directions on DRB screen and start
engine. Bring to operating temperature (engine mustbe in “closed loop” mode).
(13) With engine running at idle speed, the wordsIN RANGE should appear on screen along with 0°.This indicates correct position of oil pump drive.
(14) If a plus (+) or a minus (-) is displayed next todegree number, and/or the degree displayed is notzero, loosen but do not remove hold-down clamp bolt.Rotate oil pump drive until IN RANGE appears onscreen. Continue to rotate oil pump drive untilachieving as close to 0° as possible.
The degree scale on SET SYNC screen of DRB isreferring to fuel synchronization only. It is notreferring to ignition timing. Because of this, donot attempt to adjust ignition timing using thismethod. Rotating oil pump drive will have no effecton ignition timing. All ignition timing values are con-trolled by powertrain control module (PCM).
DESCRIPTION - 4.0LA one-piece coil rail assembly containing three
individual coils is used on the 4.0L 6–cylinder engine(Fig. 16). The coil rail must be replaced as oneassembly. The bottom of the coil is equipped with 6individual rubber boots (Fig. 16) to seal the 6 sparkplugs to the coil. Inside each rubber boot is a spring.The spring is used for a mechanical contact betweenthe coil and the top of the spark plug. These rubberboots and springs are a permanent part of the coiland are not serviced separately.
(1) The coil is bolted directly to the cylinder head(Fig. 17). One electrical connector (located at rear ofcoil) is used for all three coils.
8I - 10 IGNITION CONTROL TJ
CAMSHAFT POSITION SENSOR - 4.0L (Continued)
OPERATION - 4.0LAlthough cylinder firing order is the same as 4.0L
Jeep engines of previous years, spark plug firing isnot. The 3 coils dual-fire the spark plugs on cylinders1-6, 2-5 and/or 3-4. When one cylinder is being fired(on compression stroke), the spark to the oppositecylinder is being wasted (on exhaust stroke).
Battery voltage is supplied to the three ignitioncoils from the ASD relay. The Powertrain ControlModule (PCM) opens and closes the ignition coilground circuit for ignition coil operation.
Base ignition timing is not adjustable. By con-trolling the coil ground circuit, the PCM is able to setthe base timing and adjust the ignition timingadvance. This is done to meet changing engine oper-ating conditions.
The ignition coil is not oil filled. The windings areembedded in an epoxy compound. This provides heatand vibration resistance that allows the ignition coilto be mounted on the engine.
Because of coil design, spark plug cables (second-ary cables) are not used. The cables are integralwithin the coil rail.
REMOVAL - 4.0LA one-piece coil rail assembly containing three
individual coils is used on the 4.0L engine (Fig. 18).The coil rail must be replaced as one assembly. Thebottom of the coil is equipped with 6 individual rub-ber boots (Fig. 18) to seal the 6 spark plugs to thecoil. Inside each rubber boot is a spring. The springis used for an electrical contact between the coil andthe top of the spark plug. These rubber boots andsprings are a permanent part of the coil and are notserviced separately.
(1) Disconnect negative battery cable at battery.(2) The coil is bolted directly to the cylinder head.
Remove 4 coil mounting bolts (Fig. 19).(3) Carefully pry up coil assembly from spark
plugs. Do this by prying alternately at each end ofcoil until rubber boots have disengaged from allspark plugs. If boots will not release from sparkplugs, use a commercially available spark plug bootremoval tool. Twist and loosen a few boots from a fewspark plugs to help remove coil.
(4) After coil has cleared spark plugs, position coilfor access to primary electrical connector. Disconnectconnector from coil by pushing slide tab outwards toright side of vehicle (Fig. 20). After slide tab has beenpositioned outwards, push in on secondary releaselock (Fig. 20) on side of connector and pull connectorfrom coil.
INSTALLATION - 4.0L(1) Connect engine harness connector to coil by
snapping into position. Move slide tab towardsengine (Fig. 20) for a positive lock.
(2) Position ignition coil rubber boots to all sparkplugs. Push down on coil assembly until bolt baseshave contacted cylinder head
(3) Install 4 coil mounting bolts. Loosely tighten 4bolts just enough to allow bolt bases to contact cylin-der head. Do a final tightening of each bolt in stepsdown to 29 N·m (250 in. lbs.) torque. Do not applyfull torque to any bolt first.
DESCRIPTION - 2.4LThe coil assembly consists of 2 different coils
molded together. The assembly is mounted to the topof the engine (Fig. 21).
OPERATION - 2.4LThe coil fires two spark plugs simultaneously. One
plug is under compression, the other plug fires on theexhaust stroke (lost spark). Coil number one firescylinders 1 and 4, and coil number two fires cylinders2 and 3.
The Auto Shutdown (ASD) relay provides batteryvoltage to the ignition coil. The PCM provides aground contact (circuit) for energizing the coil(s). ThePCM will de-energize the ASD relay if it does notreceive the crankshaft position sensor and camshaftposition sensor inputs.
Base ignition timing is not adjustable. By con-trolling the coil ground circuit, the PCM is able to setthe base timing and adjust the ignition timingadvance. This is done to meet changing engine oper-ating conditions.
The ignition coil is not oil filled. The windings areembedded in an epoxy compound. This provides heatand vibration resistance that allows the ignition coilto be mounted on the engine.
Spark plug cables (secondary wires or cables) areused with the 2.4L 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. 22).(4) 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.
SPARK PLUG
DESCRIPTIONResistor type spark plugs are used.Spark plug resistance values range from 6,000 to
20,000 ohms (when checked with at least a 1000 voltspark plug tester). Do not use an ohmmeter tocheck the resistance values of the spark plugs.Inaccurate readings will result.
OPERATIONTo prevent possible pre-ignition and/or mechanical
engine damage, the correct type/heat range/numberspark plug must be used.
Always use the recommended torque when tighten-ing spark plugs. Incorrect torque can distort thespark plug and change plug gap. It can also pull theplug threads and do possible damage to both thespark plug and the cylinder head.
Remove the spark plugs and examine them forburned electrodes and fouled, cracked or broken por-celain insulators. Keep plugs arranged in the orderin which they were removed from the engine. A sin-gle plug displaying an abnormal condition indicatesthat a problem exists in the corresponding cylinder.Replace spark plugs at the intervals recommended inGroup O, Lubrication and Maintenance
Spark plugs that have low mileage may be cleanedand reused if not otherwise defective, carbon or oilfouled. Also refer to Spark Plug Conditions.
CAUTION: Never use a motorized wire wheel brushto clean the spark plugs. Metallic deposits willremain on the spark plug insulator and will causeplug misfire.
DIAGNOSIS AND TESTING - SPARK PLUGCONDITIONS
NORMAL OPERATINGThe few deposits present on the spark plug will
probably be light tan or slightly gray in color. This isevident with most grades of commercial gasoline(Fig. 23). There will not be evidence of electrodeburning. Gap growth will not average more thanapproximately 0.025 mm (.001 in) per 3200 km (2000miles) of operation. Spark plugs that have normalwear can usually be cleaned, have the electrodesfiled, have the gap set and then be installed.
Some fuel refiners in several areas of the UnitedStates have introduced a manganese additive (MMT)for unleaded fuel. During combustion, fuel with MMTcauses the entire tip of the spark plug to be coated
with a rust colored deposit. This rust color can bemisdiagnosed as being caused by coolant in the com-bustion chamber. Spark plug performance may beaffected by MMT deposits.
COLD FOULING/CARBON FOULINGCold fouling is sometimes referred to as carbon
fouling. The deposits that cause cold fouling are basi-cally carbon (Fig. 23). A dry, black deposit on one ortwo plugs in a set may be caused by sticking valvesor defective spark plug cables. Cold (carbon) foulingof the entire set of spark plugs may be caused by aclogged air cleaner element or repeated short operat-ing times (short trips).
WET FOULING OR GAS FOULINGA 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 wearcan cause wet fouling. In new or recently overhauledengines, wet fouling may occur before break-in (nor-mal oil control) is achieved. This condition can usu-ally be resolved by cleaning and reinstalling thefouled plugs.
OIL OR ASH ENCRUSTEDIf one or more spark plugs are oil or oil ash
encrusted (Fig. 24), evaluate engine condition for thecause of oil entry into that particular combustionchamber.
Fig. 23 Normal Operation and Cold (Carbon) Fouling1 - NORMAL2 - DRY BLACK DEPOSITS3 - COLD (CARBON) FOULING
Fig. 24 Oil or Ash Encrusted
8I - 14 IGNITION CONTROL TJ
SPARK PLUG (Continued)
ELECTRODE GAP BRIDGINGElectrode gap bridging may be traced to loose
deposits in the combustion chamber. These depositsaccumulate on the spark plugs during continuousstop-and-go driving. When the engine is suddenlysubjected to a high torque load, deposits partially liq-uefy and bridge the gap between electrodes (Fig. 25).This short circuits the electrodes. Spark plugs withelectrode gap bridging can be cleaned using standardprocedures.
SCAVENGER DEPOSITSFuel scavenger deposits may be either white or yel-
low (Fig. 26). They may appear to be harmful, butthis is a normal condition caused by chemical addi-tives in certain fuels. These additives are designed tochange the chemical nature of deposits and decreasespark plug misfire tendencies. Notice that accumula-tion on the ground electrode and shell area may beheavy, but the deposits are easily removed. Sparkplugs with scavenger deposits can be considered nor-mal in condition and can be cleaned using standardprocedures.
CHIPPED ELECTRODE INSULATORA chipped electrode insulator usually results from
bending the center electrode while adjusting thespark plug electrode gap. Under certain conditions,severe detonation can also separate the insulatorfrom the center electrode (Fig. 27). Spark plugs withthis condition must be replaced.
PREIGNITION DAMAGEPreignition damage is usually caused by excessive
combustion chamber temperature. The center elec-trode dissolves first and the ground electrode dis-solves somewhat latter (Fig. 28). Insulators appearrelatively deposit free. Determine if the spark plughas the correct heat range rating for the engine.Determine if ignition timing is over advanced or ifother 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 specifictemperature ranges. This depends upon the thick-ness and length of the center electrodes porcelaininsulator.)
Fig. 25 Electrode Gap Bridging1 - GROUND ELECTRODE2 - DEPOSITS3 - CENTER ELECTRODE
Fig. 26 Scavenger Deposits1 - GROUND ELECTRODE COVERED WITH WHITE OR YELLOWDEPOSITS2 - CENTER ELECTRODE
SPARK PLUG OVERHEATINGOverheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.29). 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 heatrange rating should be used. Over advanced ignitiontiming, detonation and cooling system malfunctionscan also cause spark plug overheating.
REMOVAL
2.4LIf spark plug for #2 or #3 cylinder is being
removed, throttle body must be removed. Refer toThrottle 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 helpprevent foreign material from entering combustionchamber.
(4) Remove spark plug from cylinder head using aquality socket with a rubber or foam insert.
(5) Inspect spark plug condition. Refer to SparkPlug Conditions.
4.0LOn the 4.0L 6–cylinder engine the spark plugs are
located below the coil rail assembly. To gain access toany/all spark plug(s), refer to Ignition Coil-4.0LEngine Removal/Installation.
(1) Prior to removing the spark plug, spray com-pressed air around the spark plug hole and the areaaround the spark plug. This will help prevent foreignmaterial from entering the combustion chamber.
(2) Remove the spark plug using a quality socketwith a rubber or foam insert.
(3) Inspect the spark plug condition. Refer toSpark Plugs Conditions.
CLEANING
CLEANING SPARK PLUGSThe plugs may be cleaned using commercially
available spark plug cleaning equipment. After clean-ing, file the center electrode flat with a small pointfile or jewelers file before adjusting gap.
CAUTION: Never use a motorized wire wheel brushto clean the spark plugs. Metallic deposits willremain on the spark plug insulator and will causeplug misfire.
Fig. 28 Preignition Damage1 - GROUND ELECTRODE STARTING TO DISSOLVE2 - CENTER ELECTRODE DISSOLVED
Fig. 29 Spark Plug Overheating1 - BLISTERED WHITE OR GRAY COLORED INSULATOR
8I - 16 IGNITION CONTROL TJ
SPARK PLUG (Continued)
INSTALLATIONAlways tighten spark plugs to the specified torque.
Over tightening can cause distortion. This may resultin a change in the spark plug gap, or a cracked por-celain insulator.
When replacing the spark plug and ignition coilcables, route the cables correctly and secure them inthe appropriate retainers. Failure to route the cablesproperly can cause the radio to reproduce ignitionnoise. It could cause cross ignition of the spark plugs,or short circuit the cables to ground.
2.4L
CAUTION: Spark plug tightening on the 2.4L istorque critical. The plugs are equipped with taperedseats. Do not exceed 15 ft. lbs. torque.
Special care should be taken when installing sparkplugs into the cylinder head spark plug wells. Besure 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 achange in the spark plug gap or a cracked porcelaininsulator.
(1) Start the spark plug into the cylinder head byhand to avoid cross threading.
(2) Tighten spark plugs. Refer to torque specifica-tions.
(3) Install throttle body (if necessary). Refer toThrottle Body Installation.
(4) Install air cleaner tube and housing.
4.0LSpecial care should be taken when installing spark
plugs into the cylinder head spark plug wells. Besure 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 achange in the spark plug gap or a cracked porcelaininsulator.
(1) Start the spark plug into the cylinder head byhand to avoid cross threading.
(2) Tighten spark plugs. Refer to torque specifica-tions.
(3) Install coil rail. Refer to Ignition Coil-4.0LEngine Removal/Installation.
SPARK PLUG CABLE
DESCRIPTIONSpark plug cables are used only on the 2.4L 4–cyl-
inder engine. They are sometimes referred to as sec-ondary ignition wires.
OPERATION2.4L 4–cylinder engine only: The spark plug cables
transfer electrical current from the ignition coil(s)and/or distributor, to individual spark plugs at eachcylinder. The resistive spark plug cables are of non-metallic construction. The cables provide suppressionof radio frequency emissions from the ignition sys-tem.
DIAGNOSIS AND TESTING
TESTINGCheck the spark plug cable connections for good
contact at the coil(s) and spark plugs. Terminalsshould be fully seated. The insulators should be ingood condition and should fit tightly on the coil andspark plugs. Spark plug cables with insulators thatare cracked or torn must be replaced.
Clean high voltage ignition cables with a clothmoistened with a non-flammable solvent. Wipe thecables dry. Check for brittle or cracked insulation.
When testing secondary cables for damage with anoscilloscope, follow the instructions of the equipmentmanufacturer.
If an oscilloscope is not available, spark plug cablesmay be tested as follows:
CAUTION: Do not leave any one spark plug cabledisconnected for longer than necessary during test-ing. This may cause possible heat damage to thecatalytic converter. Total test time must not exceedten minutes.
With the engine running, remove spark plug cablefrom spark plug (one at a time) and hold next to agood engine ground. If the cable and spark plug arein good condition, the engine rpm should drop andthe engine will run poorly. If engine rpm does notdrop, the cable and/or spark plug may not be operat-ing properly and should be replaced. Also checkengine cylinder compression.
With the engine not running, connect one end of atest probe to a good ground. Start the engine and runthe other end of the test probe along the entirelength of all spark plug cables. If cables are crackedor punctured, there will be a noticeable spark jumpfrom the damaged area to the test probe. Cracked,damaged or faulty cables should be replaced withresistance type cable. This can be identified by the
TJ IGNITION CONTROL 8I - 17
SPARK PLUG (Continued)
words ELECTRONIC SUPPRESSION printed on thecable jacket.
Use an ohmmeter to test for open circuits, exces-sive resistance or loose terminals. Remove the cableat ignition coil, and from spark plug. Connect ohm-meter to each end of cable. Resistance should be 250to 1000 Ohms per inch of cable. If resistance is notwithin specifications as found in the SPARK PLUGCABLE RESISTANCE chart, replace the cable. Testall spark plug cables in this manner.
SPARK PLUG CABLE RESISTANCE
MINIMUM MAXIMUM
250 Ohms Per Inch 1000 Ohms Per Inch
3000 Ohms Per Foot 12,000 Ohms Per Foot
REMOVAL - 2.4L
CAUTION: When disconnecting a high voltage cablefrom a spark plug or from the distributor cap, twistthe rubber boot slightly (1/2 turn) to break it loose(Fig. 30).
(1) Grasp the boot (not the cable) and pull it offwith a steady, even force.
INSTALLATION(1) Push the cable firmly onto the sparkplug.
