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IGNITION SYSTEM
8D - 1
IGNITION SYSTEM
CONTENTS
page
page
DESCRIPTION AND OPERATION
AUTOMATIC SHUTDOWN (ASD) RELAY . . . . . . 2
CAMSHAFT POSITION SENSOR . . . . . . . . . . . . . 3
CRANKSHAFT POSITION SENSOR . . . . . . . . . . . 2
DISTRIBUTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
IGNITION COIL . . . . . . . . . . . . . . . . . . . . . . . . . . 2
IGNITION SWITCH AND KEY LOCK
CYLINDER . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
IGNITION SYSTEM . . . . . . . . . . . . . . . . . . . . . . . 1
POWERTRAIN CONTROL MODULE . . . . . . . . . . 1
SPARK PLUG CABLES . . . . . . . . . . . . . . . . . . . . 2
SPARK PLUGS . . . . . . . . . . . . . . . . . . . . . . . . . . 2
DIAGNOSIS AND TESTING
DISTRIBUTOR CAP . . . . . . . . . . . . . . . . . . . . . . . 5
DISTRIBUTOR ROTOR . . . . . . . . . . . . . . . . . . . . 5
IGNITION COIL TEST . . . . . . . . . . . . . . . . . . . . . 4
SPARK PLUG CABLES . . . . . . . . . . . . . . . . . . . . 5
SPARK PLUG CONDITIONS . . . . . . . . . . . . . . . . 6
REMOVAL AND INSTALLATION
CAMSHAFT POSITION SENSOR . . . . . . . . . . . . 11
CRANKSHAFT POSITION SENSOR . . . . . . . . . . 10
DISTRIBUTOR . . . . . . . . . . . . . . . . . . . . . . . . . . 11
IGNITION COIL . . . . . . . . . . . . . . . . . . . . . . . . . . 9
IGNITION SWITCH AND KEY CYLINDER . . . . . 14
SHIFTER/IGNITION INTERLOCK . . . . . . . . . . . . 16
SPARK PLUG CABLE REMOVAL . . . . . . . . . . . . 8
SPARK PLUGS . . . . . . . . . . . . . . . . . . . . . . . . . . 8
SPECIFICATIONS
ENGINE FIRING ORDER—2.5L 4-CYLINDER
ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
ENGINE FIRING ORDER—4.0L 6-CYLINDER
ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
IGNITION COIL RESISTANCE . . . . . . . . . . . . . . 17
IGNITION TIMING . . . . . . . . . . . . . . . . . . . . . . . 16
SPARK PLUG CABLE RESISTANCE . . . . . . . . . 16
SPARK PLUGS . . . . . . . . . . . . . . . . . . . . . . . . . 16
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . 17
DESCRIPTION AND OPERATION
IGNITION SYSTEM
The ignition systems used on the 2.5L 4–cylinder
and the 4.0L 6–cylinder engine are basically identi-
cal. Similarities and differences between the systems
will be discussed.
The ignition system is controlled by the powertrain
control module (PCM) on all engines.
The ignition system consists of:
•
Spark Plugs
•
Ignition Coil
•
Secondary Ignition Cables
•
Distributor (contains rotor and camshaft position
sensor)
•
Powertrain Control Module (PCM)
•
Crankshaft Position, Camshaft Position, Throt-
tle Position and MAP Sensors
Fig. 1 Powertrain Control Module (PCM) Location
NOTE: Base ignition timing by rotation of distribu-
tor is not adjustable.
The PCM opens and closes the ignition coil ground
circuit to operate the ignition coil. This is done to
adjust ignition timing, both initial (base) and
POWERTRAIN CONTROL MODULE
The Powertrain Control Module (PCM) is located
in the engine compartment (Fig. 1).
The ignition system is controlled by the PCM.
8D - 2
IGNITION SYSTEM
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DESCRIPTION AND OPERATION (Continued)
advance, and for changing engine operating condi-
tions.
The amount of electronic spark advance provided
by the PCM is determined by five input factors:
engine coolant temperature, engine rpm, intake man-
ifold temperature, manifold absolute pressure and
throttle position.
SPARK PLUGS
All engines use resistor type spark plugs. Remove
the spark plugs and examine them for burned elec-
trodes and fouled, cracked or broken porcelain insu-
lators. Keep plugs arranged in the order in which
they were removed from the engine. A single 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 milage may be cleaned
and reused if not otherwise defective, carbon or oil
fouled. Refer to the Spark Plug Condition section of
this group.
DISTRIBUTOR
All engines are equipped with a camshaft driven
mechanical distributor containing a shaft driven dis-
tributor rotor. All distributors are equipped with an
internal camshaft position (fuel sync) sensor (Fig. 2).
This sensor provides fuel injection synchronization
and cylinder identification.
SPARK PLUG CABLES
Spark plug cables are sometimes referred to as sec-
ondary ignition wires. These cables transfer electrical
current from the ignition coil(s) and/or distributor, to
individual spark plugs at each cylinder. The resistive
spark plug cables are of nonmetallic construction.
The cables provide suppression of radio frequency
emissions from the ignition system.
IGNITION COIL
Battery voltage is supplied to the ignition coil pos-
itive terminal from the ASD relay.
The Powertrain Control Module (PCM) opens and
closes the ignition coil ground circuit for ignition coil
operation.
Base ignition timing is not adjustable on any
engine.
By controlling the coil ground circuit, the
PCM is able to set the base timing and adjust the
ignition timing advance. This is done to meet chang-
ing engine operating 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.
Fig. 2 Distributor and Camshaft Position Sensor-
Typical
The distributors on both the 2.5L 4-cylinder and
the 4.0L-6 cylinder engines do not have built in cen-
trifugal or vacuum assisted advance. Base ignition
timing and all timing advance is controlled by the
powertrain control module (PCM). Because ignition
timing is controlled by the PCM,
base ignition tim-
ing is not adjustable on any of these engines.
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.
AUTOMATIC SHUTDOWN (ASD) RELAY
As one of its functions, the ASD relay will supply
battery voltage to the ignition coil. The ground cir-
cuit for the ASD relay is controlled by the Powertrain
Control Module (PCM). The PCM regulates ASD
relay operation by switching the ground circuit
on-and-off.
CRANKSHAFT POSITION SENSOR
The crankshaft position sensor is mounted to the
transmission bellhousing at the left/rear side of
engine block (Fig. 3).
Engine speed and crankshaft position are provided
through the crankshaft position sensor. The sensor
generates pulses that are the input sent to the pow-
ertrain control module (PCM). The PCM interprets
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DESCRIPTION AND OPERATION (Continued)
IGNITION SYSTEM
8D - 3
Fig. 3 Crankshaft Position Sensor—Typical
the sensor input to determine the crankshaft posi-
tion. The PCM then uses this position, along with
other inputs, to determine injector sequence and igni-
tion 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.
Fig. 4 Sensor Operation—2.5L 4-Cyl. Engine
SENSOR OPERATION
The flywheel/drive plate has groups of four notches
at its outer edge. On 4.0L 6-cylinder engines there
are three sets of notches (Fig. 5). On 2.5L 4-cylinder
engines there are two sets of notches (Fig. 4).
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 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 crankshaft position sensor input.
Fig. 5 Sensor Operation—4.0L 6-Cyl. Engine
tor. Its signal is used in conjunction with the crank-
shaft position sensor to differentiate between fuel
injection and spark events. It is also used to synchro-
nize 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.
CAMSHAFT POSITION SENSOR
The camshaft position sensor is located in the dis-
tributor on all engines.
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-
8D - 4
IGNITION SYSTEM
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DESCRIPTION AND OPERATION (Continued)
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.
IGNITION SWITCH AND KEY LOCK CYLINDER
The ignition switch is located on the steering col-
umn. The Key-In-Switch is located in the ignition
switch module. For electrical diagnosis of the Key-In-
Switch, refer to Group 8U, Chime/Buzzer Warning
Systems. For removal/installation of either the key
lock cylinder or ignition switch, refer to Ignition
Switch and Key Cylinder in this group.
On vehicles equipped with an automatic transmis-
sion, a cable connects an interlock device within the
steering column assembly to the transmission floor
shift lever. This interlock device is used to lock the
transmission shifter in the PARK position when the
key is in the LOCKED or ACCESSORY position. The
interlock device is not serviceable. If repair is neces-
sary, the steering column assembly must be replaced.
Refer to Group 19, Steering for procedures. The
shifter interlock cable can be adjusted or replaced.
Refer to Group 21, Transmissions for procedures.
On vehicles equipped with a manual transmission,
a lever is located on the steering column behind the
ignition key lock cylinder. The lever must be operated
to allow rotation of the ignition key lock cylinder. The
lever mechanism is not serviced separately. If repair
is necessary, the steering column assembly must be
replaced. Refer to Group 19, Steering for procedures.
Fig. 6 Ignition Coil—2.5L Engine
DIAGNOSIS AND TESTING
IGNITION COIL TEST
To perform a complete test of the ignition coil and
its circuitry, refer to the DRB scan tool. Also refer to
the appropriate Powertrain Diagnostics Procedures
manual. To test the coil only, refer to the following:
The ignition coil (Fig. 6) or (Fig. 7) is designed to
operate without an external ballast resistor.
Inspect the ignition coil for arcing. Test the coil
according to coil tester manufacturer’s instructions.
Test the coil primary and secondary resistance.
Fig. 7 Ignition Coil—4.0L Engine
Replace any coil that does not meet specifications.
Refer to the IGNITION COIL RESISTANCE chart.
IGNITION COIL RESISTANCE
COIL MANUFACTURER
Diamond
Toyodenso
PRIMARY RESISTANCE
21-27°C (70-80°F)
0.97 - 1.18 Ohms
0.95 - 1.20 Ohms
SECONDARY RESISTANCE
21-27°C (70-80°F)
11,300 - 15,300 Ohms
11,300 - 13,300 Ohms
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DIAGNOSIS AND TESTING (Continued)
If the ignition coil is being replaced, the secondary
spark plug cable must also be checked. Replace cable
if it has been burned or damaged.
Arcing at the tower will carbonize the cable boot,
which if it is connected to a new ignition coil, will
cause the coil to fail.
If the secondary coil cable shows any signs of dam-
age, it should be replaced with a new cable and new
terminal. Carbon tracking on the old cable can cause
arcing and the failure of a new ignition coil.
IGNITION SYSTEM
8D - 5
DISTRIBUTOR CAP
Remove the distributor cap and wipe it clean with
a dry lint free cloth. Visually inspect the cap for
cracks, carbon paths, broken towers or damaged
rotor button (Fig. 8) or (Fig. 9). Also check for white
deposits on the inside (caused by condensation enter-
ing the cap through cracks). Replace any cap that
displays charred or eroded terminals. The machined
surface of a terminal end (faces toward rotor) will
indicate some evidence of erosion from normal oper-
ation. Examine the terminal ends for evidence of
mechanical interference with the rotor tip.
Fig. 9 Cap Inspection—Internal—Typical
Fig. 10 Rotor Inspection—Typical
SPARK PLUG CABLES
Fig. 8 Cap Inspection—External—Typical
DISTRIBUTOR ROTOR
Visually inspect the rotor (Fig. 10) for cracks, evi-
dence of corrosion or the effects of arcing on the
metal tip. Also check for evidence of mechanical
interference with the cap. Some charring is normal
on the end of the metal tip. The silicone-dielectric-
varnish-compound applied to the rotor tip for radio
interference noise suppression, will appear charred.
This is normal.
Do not remove the charred com-
pound.
Test the spring for insufficient tension.
Replace a rotor that displays any of these adverse
conditions.
Check the spark plug cable connections for good
contact at the coil(s), distributor cap towers, and
spark plugs. Terminals should be fully seated. The
insulators should be in good condition and should fit
tightly on the coil, distributor and spark plugs. Spark
plug cables with insulators that are cracked or torn
must be replaced.
Clean high voltage ignition cables with a cloth
moistened with a non-flammable solvent. Wipe the
cables dry. Check for brittle or cracked insulation.
TESTING
When testing secondary cables for damage with an
oscilloscope, follow the instructions of the equipment
manufacturer.

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