Automatic Shutdown (Asd) Relay; Crankshaft Position Sensor-5.2L - Jeep 1996 Grand Cherokee Service Manual

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DESCRIPTION AND OPERATION (Continued)
Do not attempt to modify the distributor hous-
ing to get distributor rotation. Distributor posi-
tion will have no effect on ignition timing. The
position of the distributor will determine fuel
synchronization only.
All 4.0L/5.2L distributors contain an internal oil
seal that prevents oil from entering the distributor
housing. The seal is not serviceable.
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.
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 V-8
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 5.2L 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.
Fig. 3 Sensor Operation—5.2L Engine
CRANKSHAFT POSITION SENSOR—4.0L ENGINE
The crankshaft position sensor is mounted to the
transmission bellhousing at the left/rear side of the
engine block (Fig. 4).
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
IGNITION SYSTEM 8D - 3