ECO mode JEEP CHEROKEE 1988 Service Repair Manual

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2.5 L 4 -C YL - V IN [ H ]

1 988 J e ep C hero ke e
1988 CHRYSLER MOTORS ENGINES
2.5L 4-Cylinder
Jeep: Cherokee, Comanche, Wagoneer, Wrangler
ENGINE CODING
ENGINE IDENTIFICATION
NOTE: For engine repair procedures not covered in this article,
see ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article
in the GENERAL INFORMATION section.
The Vehicle Identification Number (VIN) is located on the
upper left side of dash, visible through windshield. The fourth
character of the VIN identifies the engine size. The tenth character
identifies the model year.
ENGINE IDENTIFICATION CODES TABLE









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Application VIN Code
2.5L 4-Cylinder TBI .................................... H









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SPECIAL ENGINE MARKS
Some engines are produced at the factory with oversize or
undersize components. These engines are identified by a letter code
stamped between ignition coil and distributor. Letters are decoded as
follows:
* "B" indicates all cylinder bores .010" (.25 mm) oversize.
* "C" indicates all camshaft bearing bores .010" (.25 mm)
oversize.
* "M" indicates all main bearing journals .010" (.25 mm)
undersize.
* "P" indicates all connecting rod journals .010" (.25 mm)
undersize.
REMOVAL & INSTALLATION
ENGINE REMOVAL
See ENGINE REMOVAL article.
INTAKE & EXHAUST MANIFOLDS
NOTE: Throttle body removal is necessary prior to manifold
removal. Throttle body can be separated from the manifold
and secured in a designated area with vacuum hoses attached.
Removal
1) Disconnect negative battery cable. Remove air cleaner, EGR
pipe and PCV hose. Disconnect and mark all vacuum hoses and electrical
connections. Drain cooling system.
2) Remove coolant hoses from intake manifold. Remove A/C
compressor and power steering pump and mounting bracket (if equipped).\

Fig. 4: Location of ECU-Controlled Relays
Load Swap Relay
The Load Swap Relay is used on models with A/C and power
steering. The relay works in conjunction with the power steering
pressure switch to disengage the A/C compressor clutch.
If the compressor clutch is engaged when the power steering
pressure switch contacts close, the input signal from the switch to
the ECU also activates the load swap relay. The relay contacts open,
cutting off electrical feed to the compressor clutch. The clutch
remains disengaged until the pressure switch contacts reopen and
engine idle returns to normal.
NOTE: The load swap relay does not reengage the compressor clutch
immediately. The relay has a timer that delays energizing
the clutch for .5 second to ensure smooth engagement.
Fuel Pump Control Relay
Battery voltage is applied to the relay through the ignition
switch. The relay is energized when a ground is provided by the ECU.
When energized, voltage is applied to the fuel pump See Fig. 15.
A/C Clutch Relay

The ECU controls the A/C compressor clutch by means of the
A/C clutch relay. See Fig. 15.
UP-SHIFT INDICATOR LAMP
Manual transaxle vehicles are equipped with an up-shift
indicator lamp. The lamp is normally turned on when the ignition
switch is turned "ON", and is turned off when the engine starts.
The lamp will again light during engine operation, according
to engine speed and load conditions. A switch, located on the
transaxle, prevents lamp from lighting when transmission is shifted
to the next highest gear. If the shift of gears is not performed, the
ECU will turn the lamp off after 3-5 seconds.
MODES OF OPERATION
IGNITION SWITCH "ON" MODE
When the TBI system is activated by the ignition switch, the
system power relay is energized, and the fuel pump is energized by
the ECU through the fuel pump relay. The pump will operate for
approximately 1 second, unless the engine is operating or the starter
motor is engaged.
The ECU receives input from the CTS, MAT, and MAP sensors.
The up-shift indicator lamp is illuminated.
ENGINE START-UP MODE
When the starter motor is engaged, the ECU receives inputs
from the CTS and speed sensors, the starter motor relay, and the wide
open throttle switch. The fuel pump is activated by the ECU and
voltage is applied to the injector, with the ECU controlling
injection time.
The ECU determines proper ignition timing from the speed
sensor input. If the wide open throttle switch is engaged, the ECU
will deactivate the injector to prevent flooding.
ENGINE WARM-UP MODE
The ECU receives inputs from the CTS, MAT, MAP, speed, and
knock sensors. It also is informed of throttle, gear (automatic
transaxle models) and A/C control position.
The ECU provides a ground for the injector, precisely
controlling fuel delivery to the engine. The ECU also controls
ignition timing, engine idle speed and throttle stop angle. On
vehicles with manual transmissions, the up-shift indicator lamp is
controlled according to engine speed and load.
CRUISE MODE
During cruising speed, the ECU receives inputs from the CTS,
MAT, MAP, EGO, speed and knock sensors. It is also informed of
throttle, gear (automatic transaxle models), and A/C control position.\
The ECU provides a ground to the injector, precisely
controlling injector time. It also controls idle speed, throttle stop
angle, ignition timing, air/fuel mixture ratio and up-shift indicator
lamp.
DECELERATION MODE
During deceleration, the ECU receives inputs from the CTS,

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4.0 L 6 -C YL - V IN [ M ] & 4 .2 L 6 -C YL - V IN [ C ]

1 988 J e ep C hero ke e
1988 ENGINES
Chrysler Motors 4.0L & 4.2L 6-Cylinder
Jeep; Cherokee, Comanche, Wagoneer, Wrangler
ENGINE CODING
ENGINE IDENTIFICATION
NOTE: For engine repair procedures not covered in this article,
see ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article
in the GENERAL INFORMATION section.
The Vehicle Identification Number (VIN) is located on upper
left side of dash and is visible through windshield. The fourth
character identifies the engine size. The tenth character identifies
the model year.
ENGINE IDENTIFICATION CODES TABLE









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Application VIN Code
4.0L 6-Cylinder MPFI ........................ M
4.2L 6-Cylinder 2-Bbl. ...................... C









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SPECIAL ENGINE MARKS
Some engines are produced at factory with oversize or
undersize components. These engines are identified by a letter code
stamped on a boss between ignition coil and distributor. Letters are
decoded as follows:
* "B" indicates all cylinder bores are .010" (.25 mm)
oversize.
* "C" indicates all camshaft bearing bores are .010" (.25 mm)
oversize.
* "M" indicates all main bearing journals are .010" (.25 mm)
undersize.
* "P" indicates all connecting rod journals are .010" (.25 mm)
undersize.
REMOVAL & INSTALLATION
ENGINE REMOVAL
See ENGINE REMOVAL in this section.
INTAKE & EXHAUST MANIFOLD (4.0L)
WARNING: Fuel system is under pressure. Use care when removing fuel
lines to prevent personal injury.
Removal
1) Disconnect negative battery cable. Remove air inlet from
throttle plate assembly. Disconnect throttle, cruise control and
throttle valve (A/T models) cables (if equipped).
2) Disconnect and mark all vacuum and electrical connectors

These small voltage spikes give the ECU information for calculating
engine speed.
When a large tooth and notch pass the magnetic core of the
sensor, the concentration and collapse of the magnetic field created
induces a higher voltage spike into the sensor pick-up coil windings.
This higher voltage spike indicates to the ECU that a piston will soon
be at TDC (12 teeth later).
The ECU uses speed sensor information for advancing or
retarding ignition timing, dependent upon input from other sensors and
switches.
A/C "ON" Switch
This switch signals the ECU that the A/C system is energized.
This signal is used by the ECU to increase idle speed.
Starter Motor Relay
Although no switch or sensor is used, the ECU requires this
information for fuel enrichment during starting. This information is
passed on the the ECU through the starter motor relay.
Distributor Reference Signal
Although no switch or sensor is used, the ECU requires this
information for ignition timing and fuel supply. This information is
relayed to the ECU through a "synch pulse" provided by the distributor
stator. This allows the ECU to synchronize injector opening with
intake valve opening.
ELECTRONIC CONTROL MODULE (ECM)
The Electronic Control Unit (ECU) is the "brain" of the
engine control system. The ECU is located in the passenger
compartment, under left side of dash to right of steering column.
The ECU senses engine operating conditions, processes input
signals, and controls the various systems that affect vehicle
performance.
DIAGNOSTICS
The engine control system has diagnostic capabilities. Using
System Tester (M.S. 1700), diagnostics can be performed on the system
to more accurately determine faulty components. The diagnostic
connectors are located in the engine compartment at the right shock
tower (or under left side of instrument panel).
NOTE: Information for diagnosing the engine control system using
the System Tester (M.S. 1700) was not available from
manufacturer. Only component testing is provided.
ELECTRONIC SPARK ADVANCE
Based upon engine operating conditions received from the
sensors and switches, the ECU controls spark timing. The ECU triggers
the ignition coil through the ignition control module.
IDLE SPEED CONTROL
Idle speed is controlled by the ECU through the idle speed
stepper motor. A latch relay is used to program the stepper motor for
engine start-up. The relay is located on the right inner fender panel.
See Fig. 1 . The ECU energizes the latch relay when engine is in
cranking mode, and keeps the relay energized for 3-5 seconds after the
engine is stopped. In this way, the stepper motor can provide the

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A/C -H EA TE R S YSTE M - M AN UAL

1988 J e ep C hero ke e
1988 Manual A/C-Heater Systems
JEEP
* PLEASE READ THIS FIRST *
CAUTION: When discharging air conditioning system, use only approved
refrigerant recovery/recycling equipment. Make every attempt
to avoid discharging refrigerant into the atmosphere.
DESCRIPTION
On Cherokee, Comanche and Wagoneer, the Climate Control
System is an integral assembly combining air conditioning, heating and
ventilating capabilities for models with air conditioning. The A/C
registers are built into instrument panel.
On Wrangler models, a dual flow unit with the capability of
recirculating air or drawing air from outside is used. It incorporates
under-dash registers and uses a blend-air type system.
The A/C components include a compressor, condenser, receiver-
drier, a sight glass (in the receiver-to-evaporator line) and
evaporator housing. Evaporator housing contains evaporator core,
expansion valve, thermostat, wiring and drain tube. Blower motor and
fan are located in blower housing, which is attached to evaporator
housing.
Vents provided in evaporator housing are adjustable to direct
air to different positions in vehicle's interior. System controls
include fan and temperature control knobs built into lower evaporator
housing assembly or temperature and mode levers on control panel
integrated with instrument panel.
OPERATION
A/C SYSTEM CONTROLS
Temperature & Fan Control Knobs
(Wrangler)
The right rotary control knob allows selection of desired
temperature. Knob has "OFF" "1", "2" and "3" positions for different
levels of cooling. The left rotary fan switch (knob) controls blower
motor speed. Knob has "OFF", "LOW", "MED" and "HI" positions. Fan will
operate unless mode control lever is in "OFF" position.
The A/C fan switch is a 3-speed unit used in conjunction with
a blower motor resistor. Fan switch controls low, medium and high
speed operation. Switch may be serviced by removing access plate
located on lower evaporator core housing, below control panel.
The A/C temperature control switch has a thermostat unit
built-in. Cooling adjustment is done by turning knob in a clockwise
rotation. For fast, efficient system operation in hot weather, vehicle
should be purged of hot air by driving about 2-3 city blocks with at
least one window open. During this time, temperature control knob
should be rotated clockwise to "MAX" position and fan control knob
placed in "HI" position. This allows evaporator to pre-cool and avoid
typical first blast of warm air.
Temperature Control Panel
(Cherokee, Comanche & Wagoneer)
The upper temperature control (mode) lever includes "MAX",
"NORM", "BI-LEVEL", "VENT", "HEAT" and "OFF" positions. At the far end

of the scale, a symbol for defroster indicates defrost position. In
"BI-LEVEL" position, a mixture of floor heat and defroster air is
obtained.
The lower temperature control lever operates blend-air door
in heater core housing. At full right position, all air is directed
through heater core, providing maximum heat flow. At full left
position, all air is directed around heater core providing fresh air.
Control can be set in any intermediate position to provide a blend of
heated and unheated air. Heater must be in heat or defrost mode before
any air can enter vehicle.
TROUBLE SHOOTING
See JEEP TROUBLE SHOOTING at the end of this article.
REMOVAL & INSTALLATION
CONDENSER
Removal (Cherokee, Comanche & Wagoneer) NOTE: On these
models, condenser and receiver-drier are replaced
as a unit.
1) Drain radiator. Disconnect fan shroud and radiator hoses.
Disconnect automatic transmission cooler lines (if equipped).
Discharge A/C system using approved refrigerant recovery/recycling
equipment.
2) Disconnect A/C hoses from condenser. Unplug low pressure
switch. Remove radiator and condenser as an assembly. Detach condenser
retaining bolts. Separate condenser from radiator. Remove receiver-
drier from condenser.
NOTE: Plug receiver-drier openings whenever unit is removed from
condenser. Add 1 oz. of refrigerant oil (AMC No. 8132400) to
system when replacing condenser.
Installation
To install, reverse removal procedure. Fill radiator.
Evacuate, leak test, recharge and check A/C system operation.
Removal (Wrangler)
1) Discharge system (slowly to prevent loss of compressor
oil) using approved refrigerant recovery/recycling equipment. Drain
coolant. Remove fan shroud and radiator. Disconnect pressure line at
condenser. Remove condenser mounting screws. Tilt bottom of condenser
toward engine.
2) From underside of vehicle, disconnect hose attaching
receiver-drier to evaporator. Plug all openings to prevent entry of
dirt or moisture. Remove receiver-drier and condenser assembly. Remove
receiver-drier from condenser.
Installation
To install, reverse removal procedure. Fill radiator.
Evacuate, leak test, recharge and check A/C system operation.
RECEIVER-DRIER
NOTE: On Cherokee, Comanche and Wagoneer, receiver-drier is
removed with condenser and radiator as an assembly.
Removal (Wrangler)

CAN TAP INSTALLATION
FLAT TYPE SEAL CANS
On cam-lock or one-piece can taps, first turn the handle out
to the fully open position. Securely engage the locking lugs over the
flange of the can, and lock them in place by turning the cam lock or
locking nut. Screw the tap assembly into the adapter so the sealing
gasket is fully seated against the can top. Turn the tap inward to
pierce the can and close the tap. DO NOT open the tap until ready to
purge the service hose or dispense refrigerant into the system.
On 2-piece can taps, be certain the tap handle is turned
fully in, so it is closed. Check that the locking base is turned to
its outer limit. Securely engage the locking lugs over the can
flange. Turn the entire tap assembly (without disturbing the closed
setting) down into the locking base to pierce the can. Do not open
the tap until ready to dispense into system.
SCREW TYPE SEAL CANS
Ensure can tap is fully closed. Screw refrigerant can into
can tap fitting until tight. This will pierce the can. Connect tap to
center hose on manifold gauge set. DO NOT open tap until ready to
dispense R-12 into system.
WARNING: DO NOT open high side hand valve while air conditioning
system is in operation. This high pressure could rupture
can or possibly burst fitting at safety can valve,
resulting in damage and physical injury.
COMPRESSOR OIL CHECK
GENERAL PROCEDURES
Some models have compressor-mounted service valves that allow
oil checking by isolating the compressor. On all others, system must
be discharged, using approved refrigerant recovery/recycling
equipment, and compressor may need to be removed to check oil. After
oil level is checked and adjusted, A/C system must be evacuated and
recharged.
ISOLATING COMPRESSOR
1) Connect manifold gauge set to service valves on the
compressor. Close both gauge valves. Open both service valves to
themid-position.
2) Start engine and operate air conditioning. Turn suction
service valve slowly clockwise toward front-seated position. When
suction pressure is reduced to zero or less, stop engine and quickly
close suction service valve (front-seated).
3) Front-seat the discharge valve. Loosen oil check plug
slowly to release any internal pressure. Service valves can now be
removed from compressor and compressor removed from vehicle (if
necessary). Purge compressor after servicing.
PURGING COMPRESSOR
1) Remove gauge set and place caps on service valve ports.
Back-seat the suction service valve to allow refrigerant to enter
compressor.

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

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AN TI- L O CK B RAK E S A FE TY P R EC AU TIO NS

1988 J e ep C hero ke e
GENERAL INFORMATION
Anti-Lock Brake Safety Precautions
* PLEASE READ THIS FIRST *
This article is intended for general information purposes
only. This information may not apply to all makes and models. If
vehicle is equipped with Anti-Lock Brake System (ABS), refer to
appropriate ANTI-LOCK BRAKE SYSTEM article in the BRAKES section for
description, operation, depressurizing, testing, system bleeding,
trouble shooting and servicing of specific system.
WARNING: Failure to depressurize ABS could lead to physical injury.
ANTI-LOCK BRAKE SAFETY PRECAUTIONS
WARNING: Failure to depressurize ABS could lead to physical injury.
* NEVER open a bleeder valve or loosen a hydraulic line
while ABS is pressurized.
* NEVER disconnect or reconnect any electrical connectors
while ignition is on. Damage to ABS control unit may result.
* DO NOT attempt to bleed hyudarulic system without first
referring to the appropriate ANTI-LOCK BRAKE SYSTEM article
in the BRAKES section.
* Only use specially designed brake hoses/lines on ABS equipped
vehicles.
* DO NOT tap on speed sensor components (sensor, sensor rings).
Sensor rings must be pressed into hubs, NOT hammered into
hubs. Striking these components can cause demagnetization or
a loss of polarization, affecting the accuracy of the speed
signal returning to the ABS control unit.
* DO NOT mix tire sizes. Increasing the width, as long as tires
remain close to the original diameter, is acceptable. Rolling
diameter must be identical for all 4 tires. Some
manufacturers recommend tires of the same brand, style and
type. Failure to follow this precaution may cause inaccurate
wheel speed readings.
* DO NOT contaminate speed sensor components with grease. Only
use recommended coating, when system calls for an
anti-corrosion coating.
* When speed sensor components have been removed, ALWAYS check
sensor-to-ring air gaps when applicable. These specifications
can be found in each appropriate article.
* ONLY use rocommended brake fluids. DO NOT use silicone brake
fluids in an ABS equipped vehicle.
* When instlling transmittion devices (CB's, telephones, etc.)
on ABS equipped vehicles, DO NOT locate the antenna near the
ABS control unit (or any control unit).
* Disconnect all on-board computers, when using electric
welding equipment.
* DO NOT expose the ABS control unit to prolonged periods of
high heat (185
F/85C for 2 hours is generally considered a
maximum limit).