1988 JEEP CHEROKEE Service Repair Manual

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AIR C LE A N ER - T H ER M OSTA TIC

1988 J e ep C hero ke e
1988 Exhaust Emission Systems
JEEP THERMOSTATIC AIR CLEANER
DESCRIPTION
On models equipped with carburetor, a system for pre-heating
air entering carburetor is used. This system is part of the air
cleaner and maintains air temperature at a point where carburetor can
be calibrated at leaner setting to reduce hydrocarbon emissions and
improve driveability during warm-up.
These systems are vacuum-operated and consist of heat shroud
on exhaust manifold, hot air duct, thermal sensor switch, vacuum
motor, air valve assembly and reverse delay valve.
Fig. 1: Thermostatic Air Cleaner (TAC) Assembly
Courtesy of Chrysler Motors.
OPERATION

During engine warm-up, temperature sensor switch applies
vacuum to vacuum motor. Air diverter valve is held to "ON" position.
Exhaust manifold heated air flows to air cleaner. As temperature of
incoming air increases to 90
F (32C), temperature sensor opens
vacuum line to atmosphere allowing spring pressure to push valve to
"OFF" position. Air now flows from outside, through air cleaner duct
to carburetor.
AIR CLEANER TRAP DOOR
On California vehicles, spring-loaded trap door is built
into air cleaner to close off air cleaner when engine is shut off.
Door is vacuum operated.
REVERSE DELAY VALVE
Reverse delay valve is installed in vacuum line in some
vehicles to prevent trap door from closing during low engine vacuum
periods. Valve provides about 9 seconds delay before allowing trap
door to close.
Fig. 2: Cutaway View of Thermostatic Air Cleaner Assembly
Courtesy of Chrysler Motors.

TESTING
VACUUM MOTOR & TEMPERATURE SENSOR
1) Remove air cleaner assembly from vehicle and allow to
cool to room temperature. Look through air cleaner duct and observe
position of air diverter valve. It should be fully open to outside
air.
2) Reinstall assembly on carburetor and connect hot air duct
and manifold vacuum hose. Start engine and observe position of air
valve in snorkel. It should be fully closed to outside air.
3) Move throttle lever rapidly to 1/2 to 3/4 opening and
release. Air diverter valve should open and then close again. Allow
engine to warm to operating temperature and observe position of air
valve in snorkel. It should be fully open to outside air.
4) If valve does not move to fully close off outside air at
83
F (28C) or less with vacuum applied, check for binding of duct,
vacuum leaks in hose connections or disconnected vacuum motor. If
valve mechanism operates freely and no vacuum leaks are detected,
connect hose from intake manifold vacuum source directly to vacuum
motor.
5) If air valve now moves to close off outside air, replace
thermal sensor switch. If valve still does not move to close off
outside air, replace air cleaner assembly and vacuum motor assembly.
TRAP DOOR
1) With engine off, remove air cleaner and check position of
trap door. It should be closed.
2) Remove vacuum hose from intake manifold vacuum source and
apply an external vacuum source of approximately 2-4 in. Hg vacuum.
Trap door should open.
3) If door does not open, apply vacuum directly to vacuum
motor. If door does not open, check for binding and adjust as
necessary. If door swings freely, replace vacuum motor.
4) If door opens during step 3), check vacuum hose for
blockage, cracks or leaks. Correct as necessary and retest as
specified in step 2).
5) If hoses are not defective, remove reverse delay valve,
join vacuum hose and retest from step 2). If door opens, replace
reverse delay valve.
REVERSE DELAY VALVE
1) Connect external vacuum source to port on White side of
delay valve. Connect one end of 24" (610 mm) section of rubber hose
to vacuum gauge and other end to port on colored side of valve.
2) With a constant 10 in. Hg vacuum applied, note time
required for vacuum gauge pointer to move from 0-8 in. Hg.

AIR IN JE C TIO N S YSTE M

1988 J e ep C hero ke e
1988 Exhaust Emission Systems
JEEP PULSE AIR INJECTION SYSTEM
4.2L
DESCRIPTION
Pulse air injection system is used to inject fresh air into
exhaust system. When fresh air is injected into hot exhaust gases,
combustion takes place. This reduces amount of unburned fuel that
escapes into the atmosphere.
System consists of check valves, control valves, control
valve solenoids, vacuum reservoir, vacuum lines and air lines. Pulse
air system is capable of injecting air at both catalytic converter
(downstream) or at front exhaust pipe.
OPERATION
Pulse air system uses alternating positive and negative
pressure pulsations in exhaust system to draw in fresh air through
air cleaner. Check valves are used to allow fresh air into exhaust,
but prevent exhaust from flowing back into intake system.
Air is switched between upstream and downstream injection by
2 vacuum-operated control valves. Each control valve is switched by
an electrically operated-vacuum solenoid.
Vacuum solenoids are switched on and off by MCU according to
engine operating conditions. Vacuum storage tank maintains vacuum
supply to switching solenoids.
DIAGNOSIS & TESTING
1) Check condition of all hoses and lines in system. Reroute
any kinked or restricted hoses. Repair or replace any cracked or
broken hoses. To check system operation, feel for suction in
injection hoses at air cleaner.
2) If problem exists, check to see if vacuum is being
supplied to the valve. If vacuum is not present at valve(s), check
vacuum lines or ports.

Fig. 1: Jeep Pulse Air Injection System
Courtesy of Chrysler Motors.

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ALTE R NATO R - D ELC O W /IN TE G RAL R EG ULA TO R

1988 J e ep C hero ke e
1988 Alternators & Regulators
DELCO-REMY WITH INTEGRAL REGULATOR
Jeep
DESCRIPTION
There are 2 types of alternators used on these vehicles. The
12SI and 17SI series (Systems Integral), means alternator with built-
in regulator. All 12SI alternators have "Y" stator windings, while all
17SI have delta windings.
The CS130 (Charging System) alternators have a high amperage
output. This alternator does not have a diode trio.
IDENTIFICATION
Fig. 1: Alternator Terminal Identification & Locations
"S" terminal is optional on CS130.
OPERATION
CS SERIES
Regulator voltage varies to compensate for temperature.
Voltage is regulated by controlling rotor field current. Regulator
switches rotor field current "on" and "off" at a fixed frequency of
approximately 400 cycles per second.
By controlling "on" and "off" time correct system voltage can

be obtained. During high speeds "on" time may be 10 percent and "off"
time 90 percent. During low speeds with high electrical loads, "on"
time may be 90 percent and "off" time 10 percent.
SI SERIES
A rectifier bridge, connected to stator windings, contains 6
diodes (3 positive and 3 negative) molded into an assembly. This
rectifier bridge changes stator AC voltage into DC voltage, which
appears at output terminal.
Alternator field current is supplied through a diode trio
which is also connected to stator windings. A capacitor is mounted to
end frame, protecting rectifier bridge and diodes from high voltage
and suppressing radio interference noise.
TROUBLE SHOOTING
NOTE: See the TROUBLE SHOOTING - BASIC PROCEDURES article
in the GENERAL TROUBLE SHOOTING section.
TESTING
PRELIMINARY INFORMATION
NOTE: Before making electrical checks, visually inspect all
terminals for clean, tight connections. Check alternator
mounting bolts and drive belt tension. Battery must be in
good condition to test charging system.
TESTING (ON-VEHICLE)
CS SERIES
Over/Undercharged Battery (W/ STandard Instruments)
1) If an overcharging condition is suspected, run engine at a
moderate speed. Connect a voltmeter across battery terminals. If
voltmeter indicates more than 16 volts, replace alternator.
2) If an undercharging condition is suspected, disconnect
2
wire connector from alternator. Turn ignition on with engine off.
Connect a voltmeter between terminal "L" in wiring harness and ground.
Record reading.
3) If terminal "I" is used, connect voltmeter between
terminal "I" and ground. Record reading. If voltmeter reads battery
voltage, circuits are okay. If voltmeter reads zero, this indicates an
open circuit between terminal checked and battery. Repair as
necessary.
Overcharged Battery (W/ Gauges)
If an overcharging condition is suspected, run engine at a
moderate speed. Connect a voltmeter across battery terminals. If
voltmeter indicates more than 16 volts, replace alternator.
Alternator Output Test (W/ Standard Instruments Or Gauges)
1) Run engine at moderate speed, all electrical accessories
off. Measure voltage across battery, if above 16 volts, replace
alternator.
2) Connect an ammeter in circuit at "BAT" terminal of
alternator. Turn on all available accessories. Connect a battery load
tester across battery. Operate engine at 2000 RPM and adjust battery
load tester as required to obtain maximum current output while

maintaining 13 volts or more.
3) Output must be within 15 amps of rated output stamped on
alternator. If output is not within 15 amps of rated output, replace
alternator.
SI SERIES
Overcharged Or Undercharged Battery
1) If an overcharging condition is suspected, attach a
voltmeter across battery terminals. Run engine at a moderate speed
with all accessories off. If voltmeter reads 15.5 volts or more,
remove alternator for repair.
2) If an undercharging condition is suspected, turn ignition
on. Connect a voltmeter from alternator "BAT" terminal to ground.
Voltmeter should read 12 volts. Connect voltmeter between No. 1
terminal and ground. Voltmeter should read one volt or more.
3) Connect voltmeter between No. 2 terminal and ground.
Voltmeter should read 12 volts. A zero reading on any connection
indicates an open between connection and battery. Opens in the No. 2
lead may be between terminals at the crimp between harness wire and
terminal, or in wire.
Alternator Output Test
1) Connect an ammeter in circuit at "BAT" terminal of
alternator. Turn on all available accessories. Connect a carbon pile
across battery. Operate engine at 2000 RPM and adjust carbon pile as
required to obtain maximum current output.
2) Ampere output must be within 10 amps of rated output. If
output is not within 10 amps of rated output, ground field winding by
inserting a screwdriver into test hole. Repeat step 1).
3) If output is increases to within 10 amps of rated output
with field grounded, regulator is defective. If output remains below
10 amps of rated output, check field winding, diode trio, rectifier
bridge, and stator.
CAUTION: Tab is within 3/4" of casting surface. DO NOT force tool
beyond 1" into end frame. If test hole is not accessible,
proceed to BENCH TESTING.
BENCH TESTING
NOTE: There are no internal checks for CS series alternators.
SI SERIES
Rotor Field Winding Test
1) To check for grounds, attach ohmmeter leads to shaft and
slip ring (each ring in turn). If reading is not infinity, replace
rotor.
2) To test for open field, attach ohmmeter leads to each slip
ring. Resistance should measure about 2.4
2.8 ohms on 12SI series, or
1.72.1 ohms on 17SI series. If not, replace rotor.