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80-2
IGNITION SYSTEM
DESCRIPTION AND OPERATION (Continued)
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
POWERTRAIN CONTROL MODULE
The Powertrain Control Module (PCM) is
in the engine compartment (Fig. 1).
PCM
MOUNTING
BOLTS (3)
(3) 32-WAY
CONNECTOR
located
~NXI \N PONE RTRAIN
CONTROL MODULE
(PCM)
Fig. 1 Powertrain Control Module (PCM) Location
The ignition system is controlled by the PCM .
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
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.
DISTRIBUTOR
All 2.5L 4-cylinder and 4.OL 6-cylinder engines are
equipped with a camshaft driven mechanical distrib-
utor containing a shaft driven distributor rotor.
These distributors are equipped with an internal
camshaft position (fuel sync) sensor (Fig. 2) . This
sensor provides fuel injection synchronization and
cylinder identification .
DISTRIBUTOR
ASSEMBLY
TJ
Fig. 2 Distributor and Camshaft Position Sensor
(Typical Sensor Shown)
The distributors on 2.5L or 4.OL engines do not
have built in centrifugal or vacuum assisted advance .
Base ignition timing and all, timing advance is con-
trolled by the powertrain control module (PCM) .
Because ignition timing is controlled by the PCM,
base ignition timing 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 hold-down 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 .
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
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Table of Contents
Troubleshooting
