Jeep Cherokee 2000 Service Manual - page 350
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.
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 (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
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)
Fig. 3 Coil Location—4.0L Engine
1 – COIL RAIL
2 – COIL MOUNTING BOLTS (4)
3 – COIL
4 – COIL ELECTRICAL CONNECTION
XJ
IGNITION SYSTEM
8D - 3
DESCRIPTION AND OPERATION (Continued)