Automatic Shutdown (Asd) Relay; Camshaft Position Sensor; Crankshaft Position Sensor-4.0L Engine; Crankshaft Position Sensor-5.2L/5.9L - Jeep 1997 Grand Cherokee Service Manual

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DESCRIPTION AND OPERATION (Continued)
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.

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—5.2L/5.9L V-8

ENGINES

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
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.
On 5.2L/5.9L V-8 engines, the flywheel/drive plate
has 8 single notches, spaced every 45 degrees, at its
outer edge (Fig. 3).
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 8
pulses generated on V-8 engines.
The engine will not operate if the PCM does not
receive a crankshaft position sensor input.
CRANKSHAFT NOTCHES POSITION SENSOR
Fig. 3 Sensor Operation—5.2L/5.9LEngines
CRANKSHAFT POSITION SENSOR—4.0L ENGINE
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
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.
On 4.0L 6-cylinder engines, the flywheel/drive
plate has 3 sets of four notches at its outer edge (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 3
sets of four pulses generated.
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.

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
FLYWHEEL
IGNITION SYSTEM 8D - 3