Starter Motor Operation; Starter Relay Description And Operation - Jeep Cherokee 2000 Service Manual

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DESCRIPTION AND OPERATION (Continued)
Both starter motors use an overrunning clutch and
starter pinion gear unit to engage and drive the
starter ring gear, which is integral to the flywheel
(manual transmission) or torque converter drive
plate (automatic transmission) mounted on the rear
crankshaft flange. Shims are available and can be
used to adjust the 2.5L starter motor mounting posi-
tion to correct for improper starter pinion gear to
starter ring gear engagement.
The starter motors for both engines are activated
by an integral heavy duty starter solenoid switch
mounted to the overrunning clutch housing. This
electromechanical switch connects and disconnects
the feed of battery current to the starter motor
through a movable contact on one end of the solenoid
core or plunger. At the same time, the solenoid
plunger actuates a shift fork that engages and disen-
gages the starter pinion gear with a starter ring
gear. The starter solenoid has two electromagnetic
windings or coils, a pull-in coil and a hold-in coil. The
pull-in coil requires more battery current and pro-
duces a stronger electromagnetic field than the
hold-in coil.
Both starter motors are serviced only as a unit
with their starter solenoids, and cannot be repaired.
If either component is faulty or damaged, the entire
starter motor and starter solenoid unit must be
replaced.
OPERATION
When the starter solenoid pull-in coil windings are
energized the solenoid plunger is drawn into the elec-
tromagnetic coil. The solenoid plunger pulls the shift
lever in the starter motor. This engages the starter
overrunning clutch and pinion gear with the starter
ring gear on the manual transmission flywheel or on
the automatic transmission torque converter drive
plate. As the solenoid plunger reaches the end of its
travel, it moves the solenoid contact disc to complete
the high-amperage starter feed circuit and energizes
the solenoid hold-in coil windings. Battery current
now flows between the solenoid battery terminal and
the starter field terminal, energizing the starter and
cranking the engine.
Once the engine starts, the overrunning clutch pro-
tects the starter motor from damage by allowing the
starter pinion gear to spin faster than the pinion
shaft. When the solenoid plunger hold-in coil is de-
energized, the solenoid plunger return spring returns
the plunger to its relaxed position. This causes the
solenoid contact disc to open the starter feed circuit,
and the shift lever to disengage the overrunning
clutch and pinion gear unit from the starter ring
gear.
STARTER RELAY
DESCRIPTION
TERMINAL LEGEND
NUMBER IDENTIFICATION
30 COMMON FEED
85 COIL GROUND
86 COIL BATTERY
87 NORMALLY OPEN
87A NORMALLY CLOSED
Fig. 2 Starter Relay
The starter relay (Fig. 2) is an electromechanical
device that switches battery current to the pull-in
coil of the starter solenoid when the ignition switch
is turned to the Start position. The starter relay is
located in the Power Distribution Center (PDC), in
the engine compartment. See the fuse and relay lay-
out label affixed to the inside surface of the PDC
cover for starter relay identification and location.
The starter relay is a International Standards
Organization (ISO) relay. Relays conforming to the
ISO specifications have common physical dimensions,
current capacities, terminal patterns, and terminal
functions.
The starter relay cannot be repaired or adjusted
and, if faulty or damaged, it must be replaced.
OPERATION
The ISO relay consists of an electromagnetic coil, a
resistor or diode, and three (two fixed and one movable)
electrical contacts. The movable (common feed) relay
contact is held against one of the fixed contacts (nor-
mally closed) by spring pressure. When the electromag-
netic coil is energized, it draws the movable contact
away from the normally closed fixed contact, and holds
it against the other (normally open) fixed contact.
When the electromagnetic coil is de-energized,
spring pressure returns the movable contact to the
normally closed position. The resistor or diode is con-
nected in parallel with the electromagnetic coil in the
relay, and helps to dissipate voltage spikes that are
produced when the coil is de-energized.
STARTING SYSTEMS 8B - 3