Jeep Cherokee 2000 Service Manual - page 351
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 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.
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.
Fig. 4 Sensor Operation—2.5L 4-Cyl. Engine
1 – CRANKSHAFT POSITION SENSOR
2 – NOTCHES
3 – FLYWHEEL
Fig. 5 Sensor Operation—4.0L 6-Cyl. Engine
1 – CRANKSHAFT POSITION SENSOR
2 – FLYWHEEL
3 – FLYWHEEL NOTCHES
8D - 4
IGNITION SYSTEM
XJ
DESCRIPTION AND OPERATION (Continued)