1988 JEEP CHEROKEE coolant

\003
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









\









\









\









\









\









\






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









\









\









\









\









\









\






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).\

Disconnect throttle valve linkage on A/T models.
3) Remove coolant temperature sensor wire. Disconnect
throttle cable at bellcrank. Remove intake manifold bolts. Remove
intake manifold.
4) If exhaust manifold requires removal, raise and support
vehicle. Disconnect exhaust pipe. Remove oxygen sensor wire and remove
sensor. Remove manifold-to-cylinder head bolts. Remove exhaust
manifold.
Installation
1) Ensure all gasket surfaces are clean. Install manifolds
and gasket on cylinder head. Start all bolts and finger tighten.
Tighten bolts in proper sequence. See Fig. 1. Tighten bolts to
specification. See TORQUE SPECIFICATIONS table.
2) Clean oxygen sensor threads. Apply anti-seize on oxygen
sensor threads prior to installation. Install sensor and tighten to
specification. Reverse removal procedures to complete installation.
Fill and purge cooling system. See COOLING SYSTEM AIR PURGE under
ENGINE COOLING.
Fig. 1: Manifold Bolt Tightening Sequence
CYLINDER HEAD
Removal
1) Disconnect negative battery cable. Drain cooling system.
Remove air cleaner. Remove intake and exhaust manifolds. See INTAKE &
EXHAUST MANIFOLDS.
2) Disconnect and mark all hoses and electrical connections
at cylinder head. Disconnect and mark spark plug wires. Remove spark
plugs. Remove valve cover bolts.

1) Drain cooling system. Remove fan shroud and drive belts.
Remove fan assembly.
2) Disconnect heater hoses and lower radiator hose at water
pump. Remove water pump retaining bolts. Remove water pump.
Installation
Clean all gasket surfaces. Install water pump. Tighten bolts
to specification. Ensure pump turns freely. Reverse removal
procedures. Fill and purge air from cooling system.
NOTE: It may be necessary to remove heater hose to remove trapped
air if system cannot be purged using following procedures.
Cooling System Air Purge (Vehicles With Coolant Recovery)
Fill system to proper level. Place heater control to "HEAT"
position and temperature control to "WARM" or "HIGH" position. Install
coolant caps. Operate engine to normal operating temperature. Shut off
engine and allow system to cool. Add coolant to recovery bottle.
Repeat procedure to obtain correct coolant level.
Cooling System Air Purge (Vehicles Without Coolant Recovery)
Fill system to proper level. Place heater control to "HEAT"
position and temperature control to "WARM" or "HIGH" position. Operate
engine to normal operating temperature with radiator cap removed. Add
necessary coolant and install radiator cap.
NOTE: For further information on cooling system capacities and
other cooling system components, see ENGINE COOLING SYSTEMS
article.
ENGINE OILING
CRANKCASE CAPACITY
Crankcase capacity is 4 qts. (3.8 L) with oil filter change.
NORMAL OIL PRESSURE
Normal oil pressure should be 13 psi (.91 kg/cm) at 600 RPM
or 37-75 psi (2.6-5.3 kg/cm) at 1600 RPM.
OIL PRESSURE REGULATOR VALVE
Oil pressure regulator valve is located in oil pump body and
is nonadjustable.
OILING SYSTEM
Engine lubrication is provided by the distributor driven
gear-type oil pump. Oil is supplied through the full-flow oil filter
and into an internal oil passage. Internal passage runs along right
side of block and intersects lifter bores.
Oil is then routed to camshaft and crankshaft bearings. Oil
is supplied to rocker arms from the hydraulic lifters and through the
push rods. By-pass valves are located in oil filter mounting and oil
pump.
OIL PUMP
Removal
Remove oil pan. See OIL PAN REMOVAL article. Remove oil pump

emission control devices. This permits optimum engine performance
with minimum emissions.
OPERATION
The engine control system is divided into 6 sub-systems:
electronic control unit (also called the ECU or computer), sensors and\
switches, fuel control, emission control, idle speed control, and
ignition advance control.
ELECTRONIC CONTROL UNIT (ECU)
The ECU is located under the instrument panel, above the
accelerator pedal. It receives information from the 13 engine sensors
or switches to determine engine operating conditions at any particular
moment. The ECU responds to these signals by sending a control signal
to the fuel injector, fuel pump, ignition control module, idle speed
actuator (ISA) motor, EGR solenoid, and canister purge solenoid. It
also controls the Load Swap relay, and on Man. Trans. models, the up-
shift indicator lamp.
SENSORS & SWITCHES
Exhaust Gas Oxygen (EGO) Sensor
The amount of oxygen in exhaust gases varies according to the
air/fuel ratio of the intake charge. The exhaust gas oxygen sensor,
located in the exhaust pipe, detects this content and transmits a low
voltage signal to the ECU.
The outer surface of the sensor is exposed to exhaust gases,
the inner surface to outside air. The difference in the amount of
oxygen contacting the inner and outer surfaces of the sensor creates a
pressure, which results in a small voltage signal. This signal, which
is a measure of the unburned oxygen in the exhaust gas, is transmitted
to the ECU.
If the amount of oxygen in the exhaust system is low (rich
mixture), the sensor voltage signal will be high. If the mixture is
lean, the oxygen sensor will generate a low voltage signal.
The sensor has a heating element that keeps the sensor at
proper operating temperature during all operating modes.
Manifold Air/Fuel Temperature (MAT) Sensor
The manifold air/fuel temperature sensor is installed in the
intake manifold. This sensor provides a voltage signal to the ECU
representing the temperature of the air/fuel mixture in the intake
manifold. The ECU compensates for air density changes during high
temperature operation.
Coolant Temperature Sensor (CTS)
The coolant temperature sensor is located in the intake
manifold coolant jacket. This sensor provides a voltage signal to the
ECU. The ECU uses this signal to determine engine temperature. During
cold engine operation, the ECU responds by enriching the air/fuel
mixture delivered to the injector, compensating for fuel condensation
in the intake manifold, controlling engine warm-up speed, increasing
ignition advance, and inhibiting operation of the EGR system.
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor detects absolute pressure in the intake
manifold as well as ambient atmospheric pressure. This information is
supplied to the ECU, through voltage signals, as an indication of
engine load. The sensor is attached to the plenum chamber near the
hood latch. A vacuum line from the throttle body supplies the sensor

sensor. With engine warm, resistance should be less than 1000 ohms.
2) Connect one ohmmeter lead to sensor connector terminal.
Connect other lead, in turn, to ECU harness connector terminals 32
and 14. Repair wiring harness if resistance is greater than 1 ohm.
COOLANT TEMPERATURE SENSOR
1) Disconnect wiring harness from CTS sensor. Test
resistance of sensor. If resistance is not 185-100,700 ohms (3400
ohms at 70
F; 1600 ohms at 100F), replace sensor. With engine warm,
resistance should be less than 1000 ohms.
2) Connect one ohmmeter lead to sensor connector terminal.
Connect other lead, in turn to ECU harness connector terminals 15 and
32. Repair wiring harness if an open circuit is indicated.
WIDE OPEN THROTTLE (WOT) SWITCH
1) Disconnect wiring harness from WOT switch. Connect
ohmmeter leads to switch terminals, and manually open and close the
switch. When switch is closed, resistance should be infinite. A low
resistance should be indicated at wide open position. Test switch
operation several times. Replace WOT switch if defective. Reconnect
wiring harness.
2) With ignition switch "ON", connect voltmeter between pin
6 and pin 7 (ground) of diagnostic connector D2. Voltage should be
zero with switch in wide open position and greater than 2 volts in
any other position.
3) If voltage is always zero, test for short circuit to
ground in wiring harness or switch. Check for open circuit between
pin 8 of ECU connector and the switch connector. Repair or replace
wiring harness as necessary.
4) If voltage is always greater than 2 volts, test for an
open wire or connector between the switch and ground. Repair as
required.
CLOSED THROTTLE SWITCH
NOTE: It is important that all testing be done with the idle speed
actuator (ISA) motor plunger in the fully extended position
(as it would be after a normal engine shut down). If it is
necessary to extend the motor plunger to test the switch, an
ISA motor failure can be suspected. Refer to ISA motor test.
1) With ignition on, connect voltmeter positive lead to pin
13 of diagnostic connector D2. Attach negative lead to pin 7. Voltage
should be close to zero at closed throttle and greater than 2 volts
at any position other than closed throttle.
2) If the voltage is always zero, test for a short circuit
to ground in the wiring harness or switch. Test for an open circuit
between pin 25 of ECU connector and throttle switch.
3) If voltage is always more than 2 volts, test for an open
circuit in the wiring harness between the ECU and switch connector.
Also check for open circuit between the switch connector and ground.
Repair or replace wiring harness as needed.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
1) Inspect MAP sensor vacuum hose connections at sensor and
throttle body. Repair as required. Test MAP sensor output voltage at
MAP sensor connector pin B (as marked on sensor body) with the
ignition switch "ON" and engine off. See Fig. 15. Output voltage
should be 4.0-5.0 volts.

1) If all components have been checked and/or repaired, but
a system failure or problem still exists, the ECU may be at fault.
However, the ECU is a very reliable unit and must always be the final
component replaced if a doubt exists concerning the cause of a system
failure.
2) The only way to confirm an ECU malfunction is to take the
unit to an AMC dealer to have it tested. This is the only sure way to
avoid replacing a good ECU.
SYSTEM DIAGNOSIS
PRELIMINARY CHECKS
Be sure fuel is actually reaching the injector. Make sure no
air is entering the intake or exhaust system above the catalytic
converter. Before assuming an engine control system malfunction,
inspect the following systems to ensure components are in good
condition and are operating properly.
* All support systems and wiring.
* Battery connections and specific gravity.
* Electrical and vacuum connections on components and sensors.
* Emission control devices.
* Ignition system.
* Vacuum hoses.
CAUTION: Never connect or disconnect a component without turning the
ignition switch off. Never apply more than 12 volts or AC
voltage to system terminals. Disconnect battery cables
before charging it. Remove ECU if temperatures are expected
to exceed 176
F (80C), such as in a paint shop bake oven.
DIAGNOSTIC TEST CHARTS
Following are 6 different diagnostic test flow charts,
providing the shortest means of testing the system. These include:
* Ignition Switch "OFF" Chart - Tests system power for ECU
memory keep-alive voltage.
* Ignition Switch "ON" Power Chart - Tests system power
function and fuel pump power function.
* Ignition Switch "ON" Input Chart - Tests closed throttle
(idle) switch, wide open throttle (WOT) switch, manifold
absolute pressure (MAP) sensor, park/neutral switch, coolant
temperature sensor (CTS), manifold air/fuel temperature (MAT\
)
sensor and the respective switch or sensor circuits.
* System Operational Chart - Tests engine start-up and fuel
injector circuits, plus function of closed loop air/fuel
mixture, coolant temperature sensor, manifold air/fuel
temperature sensor, knock sensor and closed loop ignition
retard/advance, EGR valve and canister purge solenoid, idle
speed actuator, and A/C control.
* Basic Engine Chart - Indicates possible failures within other
engine related components.
* Man. Trans. Up-shift Chart - Tests up-shift indicator lamp
function on manual transmission vehicles.

nuts. Install motor and WOT switch bracket assembly on throttle body.
2) Connect wiring harness connector to ISA motor and WOT
switch. Connect the throttle return spring, throttle cable and cruise
control cable. Adjust ISA motor and WOT switch. Install air cleaner
assembly.
NOTE: After replacing or reinstalling the original ISA motor, be
sure motor plunger is fully extended before starting the
engine. If plunger is not fully extended, the closed
throttle switch may open prematurely, causing idle speed to
drop to approximately 400 RPM.
3) Start engine with throttle at 1/4 open position. This
prevents ISA plunger from retracting. Stop engine. When ignition is
turned off, the motor plunger will fully extend. After installation
is complete, adjust ISA as required.
ELECTRONIC CONTROL UNIT
Removal & Installation
Locate ECU in passenger compartment, below glove box. Remove
retaining screws and mounting bracket. Remove the ECU, and disconnect
wiring harness connector from ECU. Reverse removal procedure to
install.
OXYGEN SENSOR
Removal
Disconnect the wire connector from sensor, and unscrew
sensor from exhaust pipe adapter. Clean adapter threads.
Installation
1) Apply anti-seize compound to sensor threads. Do not allow
compound to adhere to any other part of sensor. Hand start the sensor
into place and tighten. Check that wire terminal ends are properly
seated in connector. Connect wire.
2) Do not push the rubber boot over sensor body lower than
1/2" (13 mm) above base of sensor. If the sensor wire should break,
sensor must be replaced. These wires cannot be spliced or otherwise
repaired.
MANIFOLD AIR TEMPERATURE & MANIFOLD ABSOLUTE PRESSURE SENSORS
Removal & Installation
Disconnect wiring harness connector from sensor. Disconnect
vacuum hose from MAP sensor. Remove sensor. Clean MAT sensor manifold
threads, and wrap with Teflon tape. To install, reverse removal
procedure.
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Allow engine to cool and release pressure from cooling
system. Remove wiring harness from sensor. Remove sensor at rear of
intake manifold, and plug hole to prevent excessive coolant loss. To
install, reverse removal procedure and replace lost coolant.
EGR VALVE & CANISTER PURGE SOLENOID
Removal & Installation
Disconnect wiring harness and vacuum hose from solenoid.
Remove solenoid and bracket as an assembly. Replace solenoid as an

from intake manifold. Disconnect fuel lines at fuel rail. Fuel lines
are removed by squeezing the 2 retaining tabs against the fuel line
and pulling the fuel line from the connector. Use caution as these
fuel lines are under pressure.
3) Loosen drive belt tensioner and remove drive belt. Remove
power steering pump and bracket from intake manifold. Remove fuel rail
retaining bolts. Remove fuel rail and injector assembly.
4) Remove intake manifold heat shield. Disconnect EGR tube
fittings. Disconnect exhaust pipe from manifold. Disconnect oxygen
sensor. Remove retaining bolts and remove manifolds.
Installation
1) Install new gasket. Install exhaust and intake manifolds
and loosely install bolts. Install EGR tube between manifolds. Tighten
manifold bolts in proper sequence see Fig. 1. Tighten to
specifications, see TORQUE SPECIFICATIONS TABLE in this article.
2) Tighten EGR tube bolts. Apply anti-seize to oxygen sensor
threads prior to installation. Reverse removal procedures for
remaining components. Tighten bolts to specification.
3) Install new "O" rings on fuel line connectors prior to
installation. Ensure "CLICK" sound is heard when installing fuel
lines. This indicates that fuel lines are properly seated.
Fig. 1: Manifold Tightening Sequence (4.0L)
Courtesy of Chrysler Motors.
INTAKE & EXHAUST MANIFOLD (4.2L)
Removal
1) Remove air cleaner. Disconnect fuel line at carburetor.
Mark and disconnect all vacuum hoses, ventilation hoses and electrical
connectors at intake manifold.
2) Disconnect throttle cable at bellcrank. On A/T models,
disconnect throttle valve rod. On all models, remove PCV hose from
manifold. Drain cooling system. Remove coolant hoses from intake