ECU JEEP CHEROKEE 1988 Service Owner's Manual
[x] Cancel search | Manufacturer: JEEP, Model Year: 1988, Model line: CHEROKEE, Model: JEEP CHEROKEE 1988Pages: 1378, PDF Size: 19.9 MB
Page 77 of 1378
![JEEP CHEROKEE 1988 Service Owners Manual proper increased enrichment for the next engine start. Idle speed is
nonadjustable.
EMISSION CONTROL
The ECU electrically controls Exhaust Gas Recirculation (EGR).\
An ECU-controlled](/img/16/57037/w960_57037-76.png "JEEP CHEROKEE 1988 Service Owners Manual proper increased enrichment for the next engine start. Idle speed is
nonadjustable.
EMISSION CONTROL
The ECU electrically controls Exhaust Gas Recirculation (EGR).\
An ECU-controlled")
proper increased enrichment for the next engine start. Idle speed is
nonadjustable.
EMISSION CONTROL
The ECU electrically controls Exhaust Gas Recirculation (EGR).\
An ECU-controlled solenoid valve is used to control EGR valve
function. This valve is located on the left inner fender panel and is
operated by the ECU in response to coolant temperature, throttle
position, and manifold pressure.
Under conditions of engine warm-up, engine idle, wide open
throttle, or rapid acceleration/deceleration, the solenoid valve is
energized, blocking vacuum to the EGR valve. At normal operating
temperatures with engine speed above idle, the solenoid valve is de-
energized, allowing normal EGR valve function.
NOTE: If the electrical connector is removed from the EGR solenoid,
EGR flow will be allowed at all times.
A/C CLUTCH CONTROL
The ECU controls the A/C compressor clutch to improve idle
quality. The A/C compressor clutch will be engaged or disengaged as
deemed necessary by the ECU through the A/C clutch relay.
SHIFT LIGHT CONTROL
The shift light system is used on all manual transmission
equipped vehicles. The ECU monitors coolant temperature, throttle
position, vehicle speed, and engine speed to control the shift light.
The ECU calculates what gear position the vehicle should be in and
uses this information to turn on the light. The light indicates the
best shift point to the driver for maximum fuel economy.
The light is tested when the ignition switch is turned on.
When the engine is started, the light should go out. A transmission-
mounted switch prevents the light from illuminating when the
transmission is shifted into high gear. The ECU turns the light off if
the shift to the next higher gear is not performed within 3-5 seconds
after light comes on.
DIAGNOSIS & TESTING
PRELIMINARY CHECKS
Before assuming that the ECU is faulty, the following systems
and components must be in good condition and operating properly:
* Air filter.
* All support systems and wiring.
* Battery connections and specific gravity.
* Compression pressure.
* Electrical and vacuum connections to components, sensors and
switches.
* Emission control devices.
* Ignition system.
* All vacuum and fuel line (hose) connections.
FUEL SYSTEM TEST
Fuel Pressure
1) Remove cap from pressure test port on fuel rail and
Page 79 of 1378
COMPONENT TESTING
Throttle Position Sensor
See THROTTLE POSITION SENSOR DIAGNOSTICS chart near the end
of this article. See Fig. 8.
Coolant Temperature Sensor (CTS) &
Manifold Air Temperature (MAT) Sensor
1) Disconnect the electrical connector from the sensor. Using
a high impedance, digital volt/ohmmeter, measure the resistance of the
sensor. If measured resistance is not as specified, replace sensor.
See the CTS & MAT SENSOR TEMPERATURE-TO-RESISTANCE VALUE table.
2) Test electrical harness resistance of both sensors by
testing between ECU harness connector "D-3" and sensor connector. Also
test between sensor connector and ECU harness connector "C-10" ("C-8"
on MAT sensor). Repair wire if open circuit is detected. Repair MAT
sensor wiring harness if resistance is greater than one ohm.
CTS & MAT SENSOR TEMPERATURE-TO-RESISTANCE VALUE
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F(C) Ohms
212 (100) .................................. 185
160 (71) ................................... 450
100 (38) .................................. 1600
70 (21) ................................... 3400
40 (4) .................................... 7500
20 (-7) ................................. 13,500
0 (-18) ................................. 25,000
-40 (-40) .............................. 100,700
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Manifold Absolute Pressure (MAP) Sensor
NOTE: Terminal identification letters are stamped on MAP sensor
body.
1) Disconnect electrical connector from sensor. With ignition
on and engine stopped, measure voltage output of sensor terminal "B".
See Fig. 4 . Ensure wiring harness is okay by also measuring voltage at
ECU terminal "C-t". Output voltage should be 4-6 volts at both points.
Repair or replace wiring harness as required.
2) With ignition on and engine stopped, measure supply
voltage of sensor terminal "C". See Fig. 4. Ensure wiring harness is
okay by also measuring voltage at ECU terminal "C-14". Supply voltage
should be 4.4-5.5 volts at both points. Repair or replace wiring
harness as required.
3) Using an ohmmeter, measure ground circuit resistance at
sensor terminal "A" and ECU connector terminal "D-3". Ensure wiring
harness is okay by also measuring resistance between ECU terminal "D-
3" and "B-11". If ohmmeter indicates an open circuit, check for
defective sensor ground connection at right side of cylinder block.
4) If ground connection is okay, replace ECU. If ECU terminal
"D-3" has short to 12-volts, repair wire before replacing ECU. Repair
or replace wiring harness as required.
Page 81 of 1378
Fig. 5: Testing Oxygen Sensor Heating
Element Resistance
Knock Sensor
Knock sensor must be tested with System Tester (M.S. 1700).
Speed Sensor
Disconnect speed sensor electrical connector from the sensor.
Using an ohmmeter, measure resistance between connector terminals "A"
and "B" (marked on connector). If reading is not 125-275 ohms with
engine at normal operating temperature, replace speed sensor.
"Synch Pulse" (Stator)
1) Using an analog voltmeter, insert positive probe into Blue
wire at distributor connector. Insert negative probe into Gray wire
with tracer at distributor connector.
NOTE: Do not remove connector from distributor. Insert voltmeter
leads from rear of connector. Do not puncture wire.
2) With voltmeter set on "15-Volt A/C" scale, turn ignition
on. Voltmeter should indicate 5 volts. If voltage is indicated, go to
step 4). If no voltage is indicated, check voltmeter leads for good
connection and go to next step.
3) If there is still no voltage reading, turn ignition off
and remove ECU. Reconnect harness and turn ignition off and remove
ECU. Reconnect harness and turn ignition on. Check for voltage between
ECU pin "C-16" and good ground. If voltage still does not register,
test system with System Tester (M.S. 1700).
4) If 5 volts was detected, check for continuity at the
following points:
* Between Blue wire at distributor connector and terminal "C-16"
at ECU.
* Between Gray wire with tracer at distributor connector and
terminal "C-5" at ECU.
* Between Black wire at distributor connector and good ground.
Page 82 of 1378
If no continuity is shown, repair wiring harness. If
continuity is shown, reconnect voltmeter as in step 2).
5) While observing voltmeter, crank engine. Voltmeter needle
should fluctuate back and forth during engine cranking. This verifies
proper operation of distributor stator. If voltmeter needle does not
fluctuate, replace stator.
EGR Solenoid Valve
1) Make sure vacuum is present at port "C" of the solenoid.
See Fig. 6 . Remove vacuum connector from ports "A" and "B" of
solenoid. Connect vacuum gauge to port "B". Start engine and run at
idle. Vacuum should not be present at port "B".
2) Disconnect electrical connector from solenoid. Vacuum
should now be present at port "B". Stop engine. Reconnect electrical
connector at solenoid. Remove vacuum gauge and reconnect vacuum hoses.
Relays - General Testing
1) The relays used on the 4.0L engine are all of the same
basic construction and design. Terminal No. 30 is usually connected to
battery voltage ("switched" or battery positive at all times).
Terminal No. 87A is connected to terminal No. 30 in de-energized
position.
2) Terminal No. 87 is connected to terminal No. 30 in the
energized position. This connection supplies battery voltage to the
operated device.
3) Terminal No. 86 is connected to the electromagnet of the
operated device; usually through a "switched" power source. Terminal
No. 85 is connected to the electromagnet of the operated device;
usually grounded through a switch or the ECU.
NOTE: Not all relays have battery voltage applied at terminal No.
30. Some may have battery voltage applied at terminal Nos. 87
or 87A. Check design of relay before testing.
4) When testing relays, there should be continuity between
terminal Nos. 87A and 30 when relay is in de-energized position.
Resistance between terminal Nos. 85 and 86 should be 70-80 ohms for
resistor-type relays and 81-91 ohms for diode-type relays.
Fig. 6: Testing EGR Solenoid Valve
Starter Motor Relay
1) Disconnect electrical connectors from terminals "I" and
"G". Using an ohmmeter, measure resistance between the terminals.
Page 84 of 1378
ELECTRONIC CONTROL UNIT (ECU)
Removal & Installation
Information not available from manufacturer.
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Drain cooling system. Remove air cleaner assembly. Disconnect
electrical connector and remove sensor from block. To install, reverse
removal procedure. Refill cooling system.
OXYGEN (O2) SENSOR
Removal & Installation
Raise and support vehicle. Disconnect electrical connector
from sensor. Remove sensor from exhaust manifold. Install and tighten
sensor to 35 ft. lbs. (47 N.m). Reconnect electrical connector. Lower
vehicle.
THROTTLE POSITION SENSOR (TPS)
Removal
Disconnect electrical connector from TPS. Bend lock tabs away
from retaining screws and remove screws. Remove TPS.
Installation
With throttle valve in normal closed position, install TPS.
Install TPS retaining screws. Perform OUTPUT CHECK.
NOTE: Throttle position sensor is nonadjustable. Only output
voltage can be monitored.
Output Check (Manual Transmission Only)
1) Connect negative lead of digital voltmeter to terminal "B"
and positive lead to terminal "A" of TPS connector. Do not disconnect
electrical connector. Insert leads through back of connector. It may
be necessary to remove throttle body from vehicle to gain access to
connector.
2) Turn ignition on, engine off. With throttle closed and
resting against idle stop, input voltage should be about 5 volts. Move
positive lead from terminal "B" to terminal "C" and read voltage
output. Output voltage should be about 0.8 volt with throttle closed
and resting against idle stop.
3) If voltage is not as specified, loosen lower retaining
screw and pivot sensor for large adjustments. Loosen upper retaining
screw and pivot sensor for small adjustments. Adjust sensor so output
voltage reading equals 16 percent of input voltage. If voltage
specifications cannot be obtained, replace sensor. Remove voltmeter.
Tighten screws and bend retaining tabs into position.
ALL OTHER SENSORS, SOLENOIDS & SWITCHES
Removal & Installation
Removal of sensors, switches, and solenoids is accomplished
by disconnecting the electrical and/or vacuum connectors and removing
or detaching the component. To install, reverse removal procedure.
TESTING
NOTE: Refer to Figs. 8-10 for Testing information.
Page 87 of 1378
Fig. 10: ECU Connector Pin & Diagnostic Connector Pin Identification
WIRING DIAGRAM
Page 93 of 1378
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EAC Electric Assist Choke")
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EAC Electric Assist Choke
EACV Electric Air Control Valve
EBCM Electronic Brake Control Module
ECA Electronic Control Assembly
ECAT Electronically Controlled Automatic Transaxle
ECM Electronic Control Module
ECT Engine Coolant Temperature Sensor
ECU Electronic Control Unit or Engine Control Unit
EDF Electric Drive Fan relay assembly
EDIS Electronic Distributorless Ignition System
EEC Electronic Engine Control
EECS Evaporative Emission Control System
EEPROM Electronically Erasable PROM
EFE Early Fuel Evaporation
EFI Electronic Fuel Injection
EGO Exhaust Gas Oxygen sensor (see HEGO)
EGR Exhaust Gas Recirculation system
EGRC EGR Control solenoid or system
EGRV EGR Vent solenoid or system
EMR Emission Maintenance Reminder Module
ESA Electronic Spark Advance
ESC Electronic Spark Control
EST Electronic Spark Timing
ETR Emergency Tensioning Retractor
EVAP Fuel Evaporative System
EVIC Electronic Vehicle Information Center
EVO Electronic Variable Orifice
EVP EGR Valve Position Sensor
EVR EGR Valve Regulator
EVRV Electronic Vacuum Regulator Valve
Elect. Electronic
Eng. Engine
Evap. Evaporative
Exc. Except
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"F" ABBREVIATION TABLE
"F" ABBREVIATION TABLE \
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ABBREVIATION DEFINITION
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F Fahrenheit (Degrees)
F/B Fuse Block
FBC Feedback Carburetor
FI Fuel Injector or Fuel Injection
FICD Fast Idle Control Device
FIPL Fuel Injector Pump Lever
FP Fuel Pump
FPM Fuel Pump Monitor
FPR-VSV Fuel Pressure Regulator Vacuum Switching Valve
FWD Front Wheel Drive
Fed. Federal
Ft. Lbs. Foot Pounds
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"G" ABBREVIATION TABLE
"G" ABBREVIATION TABLE \
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ABBREVIATION DEFINITION
Page 108 of 1378
panel to gain access to blower motor mounting screws.
2) Remove screws attaching evaporator housing to instrument
panel and mounting bracket. Lower evaporator housing and pull hoses
and grommet through opening.
Installation
To install, reverse removal procedure. Evacuate, leak test,
recharge and check A/C system for proper operation.
EXPANSION VALVE
Removal (Cherokee, Comanche & Wagoneer)
Discharge A/C system using approved refrigerant
recovery/recycling equipment. Disconnect A/C hoses from expansion
valve. Disconnect expansion valve from evaporator core inlet and
outlet tubes. Remove expansion valve.
Installation
To install, reverse removal procedure. Evacuate, leak test,
recharge and check A/C system operation.
NOTE: The expansion valve is pre-set and should not be adjusted. A
faulty valve requires replacement.
Removal (Wrangler)
1) Discharge system using approved refrigerant
recovery/recycling equipment. Remove evaporator housing. Remove
insulation wrapped around suction line and expansion valve.
2) Mark capillary tube location on suction line. Disconnect
inlet and outlet connections, capillary tube clamp and equalizer tube.
Remove expansion valve.
Installation
1) Clean suction line to provide positive contact with
replacement expansion valve capillary tube. Connect inlet and outlet
hoses. Clamp capillary tube securely at marked position and connect
equalizer tube.
2) Wrap expansion valve and line with insulation. Install
evaporator housing assembly. Evacuate, leak test, recharge and check
A/C system operation.
TEMPERATURE CONTROL THERMOSTAT
Removal (Cherokee, Comanche & Wagoneer)
1) Disconnect battery ground. Remove console (if equipped).
Remove lower instrument panel. Disconnect electrical connection at
thermostat. See Fig. 3.
2) Remove capillary tube retaining screw. Remove thermostat
retaining screws. Remove capillary tube from tube guide hole.
Installation
1) To install, feed capillary tube through tube guide hole
until Red tape on capillary tube just enters hole in housing. Install
capillary tube retaining screw and clip.
2) Install thermostat retaining screws and attach electrical
connection. To complete installation, reverse removal procedure.
CAUTION: Handle capillary tube with care to avoid bends or kinks
which could cause thermostat to malfunction.
Removal (Wrangler)
Remove evaporator housing assembly. Remove lower cover.
Page 141 of 1378
conductors exposed ..... A .. Require repair or replacement.
Insulation damaged,
conductors not exposed . 1 .. Suggest repair or replacement.
Missing ................. C ............ Require replacement.
Routed incorrectly ...... B ................. Require repair.
Secured incorrectly ..... B ................. Require repair.
Terminal broken ......... A .. Require repair or replacement.
Terminal burned, affecting
performance ............ A ........... (1) Require repair or
replacement.
Terminal burned, not
affecting performance .. 2 .. Suggest repair or replacement.
Terminal corroded,
affecting performance .. A .. Require repair or replacement.
Terminal corroded, not
affecting performance .. 2 .. Suggest repair or replacement.
Terminal loose, affecting
performance ............ B .. Require repair or replacement.
Terminal loose, not
affecting performance .. 1 .. Suggest repair or replacement.
( 1) - Determine cause and correct prior to replacement
of part.
( 2) - Inoperative includes intermittent operation.
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FUSIBLE LINKS
See FUSES, FUSIBLE LINKS AND CIRCUIT BREAKERS .
GASKETS
GASKET INSPECTION \
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Condition Code Procedure
Leaking ................. A ........... ( 1) Require repair or
replacement.
( 1) - Require inspection of mating and sealing surface and
repair or replace as necessary.
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HEATER CASES
See PLENUMS.
HEATER CONTROL VALVES
HEATER CONTROL VALVE INSPECTION \
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Condition Code Procedure
Application incorrect ... B ............ Require replacement.
Attaching hardware
broken ................. A ... Require repair or replacement
of hardware.
Attaching hardware
missing ................ C .......... Require replacement of
hardware.
Attaching hardware not
functioning ............ A ... Require repair or replacement
Page 156 of 1378
specification .......... A .. Require repair or replacement.
Circuit shorted ......... A .. Require repair or replacement.
Connector melted,
affecting performance .. A ........... (1) Require repair or
replacement.
Connector melted, not
affecting performance .. 2 ........... ( 1) Suggest repair or
replacement.
Connector missing ....... C ............ Require replacement.
Diode open .............. A .. Require repair or replacement.
Diode shorted ........... A .. Require repair or replacement.
Insulation damaged,
conductors exposed ..... A .. Require repair or replacement.
Insulation damaged,
conductors not exposed . 1 ............ Suggest replacement.
Protective shield
(conduit) melted ....... B ........ ( 1) Require replacement.
Protective shield
(conduit) missing ...... C ............ Require replacement.
Routed incorrectly ...... B ................. Require repair.
Secured incorrectly ..... B ................. Require repair.
Terminal broken ......... A .. Require repair or replacement.
Terminal burned, affecting
performance ............ A ........... ( 1) Require repair or
replacement.
Terminal burned, not
affecting performance .. 2 .. Suggest repair or replacement.
Terminal corroded,
affecting performance .. A .. Require repair or replacement.
Terminal corroded, not
affecting performance .. 2 .. Suggest repair or replacement.
Terminal loose, affecting
performance ............ B .. Require repair or replacement.
Terminal loose, not
affecting performance .. 1 .. Suggest repair or replacement.
Voltage drop out of
specification .......... A .. Require repair or replacement.
( 1) - Determine cause and correct prior to repair or
replacement of part.
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