exj 8d, JEEP Manuals, Electronic Service Manual (jeep cherokee xj do 2000)
[ Pobierz całość w formacie PDF ]
XJ
IGNITION SYSTEM
8D - 1
IGNITION SYSTEM
TABLE OF CONTENTS
page
page
DESCRIPTION AND OPERATION
CAMSHAFT POSITION SENSOR—4.0L
IGNITION SWITCH AND KEY LOCK
DIAGNOSIS AND TESTING
IGNITION SWITCH AND KEY LOCK
REMOVAL AND INSTALLATION
CAMSHAFT POSITION SENSOR—2.5L
CAMSHAFT POSITION SENSOR—4.0L
SPECIFICATIONS
ENGINE FIRING ORDER—2.5L 4-CYLINDER
ENGINE FIRING ORDER—4.0L 6-CYLINDER
DESCRIPTION AND OPERATION
4.0L 6–Cylinder Engine:
The 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 compression
stroke), the spark to the opposite cylinder is being
wasted (on exhaust stroke). The one-piece coil bolts
directly to the cylinder head. Rubber boots seal the
secondary terminal ends of the coils to the top of all
6 spark plugs. One electrical connector (located at
the 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 on either engine. A
distrib-
utor is not used
with the 4.0L engine.
The ignition system is controlled by the Powertrain
Control Module (PCM).
The ignition system consists of:
²
IGNITION SYSTEM
DESCRIPTION
Two different ignition systems are used. One type
is used for the 2.5L 4–cylinder engine. The other is
used for the 4.0L 6–cylinder engine.
OPERATION
2.5L 4–Cylinder Engine:
The ignition system is controlled by the Powertrain
Control Module (PCM).
The ignition system consists of:
²
Spark Plugs
²
Ignition Coil
²
Secondary Ignition Cables
Distributor (contains rotor and camshaft position
sensor)
²
²
Spark Plugs
Powertrain Control Module (PCM)
²
Ignition Coil(s)
Crankshaft Position, Camshaft Position, Throt-
tle Position and MAP Sensors
²
²
Powertrain Control Module (PCM)
 8D - 2
IGNITION SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)
SPARK PLUGS
²
Crankshaft Position Sensor
²
Camshaft Position Sensor
The MAP, TPS, IAC and ECT also have an effect
on the control of the ignition system.
²
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.
DISTRIBUTOR-2.5L ENGINE
DESCRIPTION
The 2.5L engine is equipped with a camshaft
driven mechanical distributor (Fig. 1) containing a
shaft driven distributor rotor. The distributor is also
equipped with an internal camshaft position (fuel
sync) sensor (Fig. 1).
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. 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-
gle plug displaying an abnormal condition indicates
that a problem exists in the corresponding cylinder.
Replace spark plugs at the intervals recommended in
Group O, Lubrication and Maintenance
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.
Fig. 1 Distributor and Camshaft Position Sensor-
2.5L Engine
1 – SYNC SIGNAL GENERATOR
2 – CAMSHAFT POSITION SENSOR
3 – PULSE RING
4 – DISTRIBUTOR ASSEMBLY
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.
OPERATION
The distributor does not have built in centrifugal
or vacuum assisted advance. Base ignition timing
and all timing advance is controlled by the Power-
train Control Module (PCM). Because ignition timing
is controlled by the PCM,
base ignition timing is
not adjustable.
The distributor is locked in place by a fork with a
slot located on the distributor housing base. The dis-
tributor holddown clamp bolt passes through this slot
when installed. Because the distributor position is
locked when installed, its rotational position can not
be changed.
Do not attempt to modify the dis-
tributor housing to get distributor rotation.
Distributor position will have no effect on igni-
tion timing. The position of the distributor will
determine fuel synchronization only.
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
SPARK PLUG CABLES-2.5L ENGINE
DESCRIPTION
Spark plug cables are used only on the 2.5L
engine. They are sometimes referred to as secondary
ignition wires.
OPERATION
The spark plug cables transfer electrical current
from the ignition coil(s) and/or distributor, to individ-
ual spark plugs at each cylinder. The resistive spark
plug cables are of nonmetallic construction. The
cables provide suppression of radio frequency emis-
sions from the ignition system.
 XJ
IGNITION SYSTEM
8D - 3
DESCRIPTION AND OPERATION (Continued)
IGNITION COIL-2.5L ENGINE
DESCRIPTION
A single ignition coil is used with the 2.5L 4–cylin-
der engine. The coil is not oil filled. The coil windings
are embedded in an epoxy compound. This provides
heat and vibration resistance that allows the coil to
be mounted on the engine.
OPERATION
The Powertrain Control Module (PCM) opens and
closes the ignition coil ground circuit for ignition coil
operation.
Battery voltage is supplied to the ignition coil pos-
itive terminal from the ASD relay. If the PCM does
not see a signal from the crankshaft and camshaft
sensors (indicating the ignition key is ON but the
engine is not running), it will shut down the ASD cir-
cuit.
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.
Fig. 2 Ignition Coil Assembly—4.0L 6–Cylinder
Engine
1 – CYL. #6
2 – CYL. #5
3 – CYL. #4
4 – CYL. #3
5 – CYL. #2
6 – CYL. #1
7 – COILS (3)
8 – MOUNTING BOLTS (4)
9 – BOLT BASES (4)
10 – RUBBER BOOTS (6)
IGNITION COIL—4.0L ENGINE
DESCRIPTION
A one-piece coil rail assembly containing three
individual coils is used on the 4.0L 6–cylinder engine
(Fig. 2). The coil rail must be replaced as one assem-
bly. The bottom of the coil is equipped with 6 individ-
ual rubber boots (Fig. 2) to seal the 6 spark plugs 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.
(1) The coil is bolted directly to the cylinder head
(Fig. 3). One electrical connector (located at rear of
coil) is used for all three coils.
OPERATION
Although cylinder firing order is the same as 4.0L
Jeep engines of previous 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 compression stroke), the spark to the opposite
cylinder is being wasted (on exhaust stroke).
Battery voltage is supplied to the three ignition
coils from the ASD relay. The Powertrain Control
Module
Fig. 3 Coil Location—4.0L Engine
1 – COIL RAIL
2 – COIL MOUNTING BOLTS (4)
3 – COIL
4 – COIL ELECTRICAL CONNECTION
(PCM)
opens
and
closes
the
ignition
coil
ground circuit 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
 8D - 4
IGNITION SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)
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. The cables are integral
within the coil rail.
CRANKSHAFT POSITION SENSOR
DESCRIPTION
The Crankshaft Position (CKP) sensor is located
near the outer edge of the flywheel (starter ringear).
OPERATION
Engine speed and crankshaft position are provided
through the CKP sensor. The sensor generates pulses
that are the input sent to the Powertrain Control
Module (PCM). The PCM interprets the sensor input
to determine the crankshaft position. The PCM then
uses this position, along with other inputs, to deter-
mine injector sequence and ignition timing.
The sensor is a hall effect device combined with an
internal magnet. It is also sensitive to steel within a
certain distance from it.
The flywheel/drive plate has groups of four notches
at its outer edge. On 2.5L 4-cylinder engines there
are two sets of notches (Fig. 4). On 4.0L 6-cylinder
engines there are three sets of notches (Fig. 5).
The notches cause a pulse to be generated when
they pass under the sensor. The pulses are the input
to the PCM. For each engine revolution there are two
groups of four pulses generated on 2.5L 4-cylinder
engines. There are 3 groups of four pulses generated
on 4.0L 6-cylinder engines.
The trailing edge of the fourth notch, which causes
the
Fig. 4 Sensor Operation—2.5L 4-Cyl. Engine
1 – CRANKSHAFT POSITION SENSOR
2 – NOTCHES
3 – FLYWHEEL
pulse,
is
four
degrees
before
top
dead
center
(TDC) of the corresponding piston.
The engine will not operate if the PCM does not
receive a CKP sensor input.
CAMSHAFT POSITION SENSOR-2.5L ENGINE
DESCRIPTION
On the 2.5L 4–cylinder engine the Camshaft Posi-
tion (CMP) sensor is located in the distributor.
Fig. 5 Sensor Operation—4.0L 6-Cyl. Engine
1 – CRANKSHAFT POSITION SENSOR
2 – FLYWHEEL
3 – FLYWHEEL NOTCHES
OPERATION
The sensor contains a hall effect device called a
sync signal generator to generate a fuel sync signal.
This sync signal generator detects a rotating pulse
ring (shutter) on the distributor shaft. The pulse ring
rotates 180 degrees through the sync signal genera-
tor. Its signal is used in conjunction with the Crank-
shaft Position (CKP) sensor to differentiate between
fuel injection and spark events. It is also used to syn-
chronize the fuel injectors with their respective cylin-
ders.
 XJ
IGNITION SYSTEM
8D - 5
DESCRIPTION AND OPERATION (Continued)
When the leading edge of the pulse ring (shutter)
enters the sync signal generator, the following occurs:
The interruption of magnetic field causes the voltage
to 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.
CAMSHAFT POSITION SENSOR—4.0L ENGINE
DESCRIPTION
The Camshaft Position Sensor (CMP) on the 4.0L
6–cylinder engine is bolted to the top of the oil pump
drive shaft assembly (Fig. 6). The sensor and drive
shaft assembly is located on the right side of the
engine near the oil filter (Fig. 7).
Fig. 7 CMP Location—4.0L Engine
1 – OIL FILTER
2 – CAMSHAFT POSITION SENSOR
3 – CLAMP BOLT
4 – HOLD-DOWN CLAMP
5 – MOUNTING BOLTS (2)
6 – ELEC. CONNECTOR
pulse ring (shutter) on the oil pump drive shaft (Fig.
6). The pulse ring rotates 180 degrees through the
sync 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 also
used
to
synchronize
the
fuel
injectors
with
their
respective 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 voltage
to 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.
Fig. 6 CMP and Oil Pump Drive Shaft—4.0L Engine
1 – CAMSHAFT POSITION SENSOR
2 – MOUNTING BOLTS (2)
3 – PULSE RING
4 – DRIVE GEAR (TO CAMSHAFT)
5 – OIL PUMP DRIVESHAFT
6 – SENSOR BASE (OIL PUMP DRIVESHAFT ASSEMBLY)
IGNITION SWITCH AND KEY LOCK CYLINDER
DESCRIPTION
The electrical ignition switch is located on the
steering column. It is used as the main on/off switch-
ing device for most electrical components. The
mechanical key lock cylinder is used to engage/disen-
gage the electrical ignition switch.
OPERATION
The 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 rotating
Â
[ Pobierz całość w formacie PDF ]