JEEP CHEROKEE 1988 Service Repair Manual

Fig. 10: Typical Negative Backpressure EGR Valve
Courtesy of General Motors Corp.
Digital EGR Valve
The digital EGR valve operates independently of engine
manifold vacuum. This valve controls EGR flow through 3 orifices.

These 3 orifices are opened and closed by electric solenoids. The
solenoids are, in turn, controlled by the Electronic Control Module
(ECM). When a solenoid is energized, the armature with attached shaft
and swivel pintle is lifted, opening the orifice. See Fig. 11.
The ECM uses inputs from the Coolant Temperature Sensor
(CTS), Throttle Position Sensor (TPS) and Mass Airflow (MAF) senso\
rs
to control the EGR orifices to make 7 different combinations for
precise EGR flow control. At idle, the EGR valve allows a very small
amount of exhaust gas to enter the intake manifold. This EGR valve
normally operates above idle speed during warm engine operation.
Verify EGR valve is present and not modified or purposely
damaged. Ensure thermal vacuum switches, pressure transducers, speed
switches, etc., (if applicable) are not by-passed or modified. Ensure
vacuum hose(s) to EGR valve is not plugged. Ensure electrical
connector to EGR valve is not disconnected.
Fig. 11: Typical Digital EGR Valve
Courtesy of General Motors Corp.
Integrated Electronic EGR Valve
This type functions similar to a ported EGR valve with a

remote vacuum regulator. The internal solenoid is normally open, which
causes the vacuum signal to be vented off to the atmosphere when EGR
is not controlled by the Electronic Control Module (ECM). The solenoid\
valve opens and closes the vacuum signal, controlling the amount of
vacuum applied to the diaphragm. See Fig. 12.
The electronic EGR valve contains a voltage regulator, which
converts ECM signal and regulates current to the solenoid. The ECM
controls EGR flow with a pulse width modulated signal based on
airflow, TPS and RPM. This system also contains a pintle position
sensor, which works similarly to a TPS sensor. As EGR flow is
increased, the sensor output increases.
Verify EGR valve is present and not modified or purposely
damaged. Ensure thermal vacuum switches, pressure transducers, speed
switches, etc., (if applicable) are not by-passed or modified. Ensure
electrical connector to EGR valve is not disconnected.
Fig. 12: Cutaway View Of Typical Integrated Electronic EGR Valve
Courtesy of General Motors Corp.
SPARK CONTROLS (SPK)

Spark control systems are designed to ensure the air/fuel
mixture is ignited at the best possible moment to provide optimum
efficiency and power and cleaner emissions.
Ensure vacuum hoses to the distributor, carburetor, spark
delay valves, thermal vacuum switches, etc., are in place and routed
properly. On Computerized Engine Controls (CEC), check for presence of\
required sensors (O2, MAP, CTS, TPS, etc.). Ensure they have not been
tampered with or modified.
Check for visible modification or replacement of the feedback
carburetor, fuel injection unit or injector(s) with a non-feedback
carburetor or fuel injection system. Check for modified emission-
related components unacceptable for use on pollution-controlled
vehicles.
AIR INJECTION SYSTEM (AIS)
Air Pump Injection System (AP)
The air pump is a belt-driven vane type pump, mounted to
engine in combination with other accessories. The air pump itself
consists of the pump housing, an inner air cavity, a rotor and a vane
assembly. As the vanes turn in the housing, filtered air is drawn in
through the intake port and pushed out through the exhaust port. See
Fig. 13 .
Check for missing or disconnected belt, check valve(s),
diverter valve(s), air distribution manifolds, etc. Check air
injection system for proper hose routing.
Fig. 13: Typical Air Pump Injection System
Courtesy of General Motors Corp.
Pulsed Secondary Air Injection (PAIR) System
PAIR eliminates the need for an air pump and most of the
associated hardware. Most systems consists of air delivery pipe(s),
pulse valve(s) and check valve(s). The check valve prevents exhaust
gases from entering the air injection system. See Fig. 14.
Ensure required check valve(s), diverter valve(s), air
distribution manifolds, etc., are present. Check air injection system
for proper hose routing.

Fig. 14: Typical Pulsed Secondary Air Injection System
Courtesy of General Motors Corp.
OXYGEN SENSOR (O2)
The O2 sensor is mounted in the exhaust system where it
monitors oxygen content of exhaust gases. Some vehicles may use 2 O2
sensors. The O2 sensor produces a voltage signal which is proportional
to exhaust gas oxygen concentration (0-3%) compared to outside oxygen
(20-21%). This voltage signal is low (about .1 volt) when a lean
mixture is present and high (1.0 volt) when a rich mixture is present.\
As ECM compensates for a lean or rich condition, this voltage
signal constantly fluctuates between high and low, crossing a
reference voltage supplied by the ECM on the O2 signal line. This is
referred to as cross counts. A problem in the O2 sensor circuit should
set a related trouble code.
COMPUTERIZED ENGINE CONTROLS (CEC)
The CEC system monitors and controls a variety of
engine/vehicle functions. The CEC system is primarily an emission
control system designed to maintain a 14.7:1 air/fuel ratio under most
operating conditions. When the ideal air/fuel ratio is maintained, the
catalytic converter can control oxides of nitrogen (NOx), hydrocarbon
(HC) and carbon monoxide (CO) emissions.
The CEC system consists of the following sub-systems:
Electronic Control Module (ECM), input devices (sensors and switches)\
and output signals.

EARLY FUEL EVAPORATION (EFE)
The EFE valve is actuated by either a vacuum actuator or a
bimetal spring (heat-riser type). The EFE valve is closed when engine
is cold. The closed valve restricts exhaust gas flow from the exhaust
manifold. This forces part of the exhaust gas to flow up through a
passage below the carburetor. As the exhaust gas quickly warms the
intake mixture, distribution is improved. This results in better cold
engine driveability, shorter choke periods and lower emissions.
Ensure EFE valve in exhaust manifold is not frozen or rusted
in a fixed position. On vacuum-actuated EFE system, check EFE thermal
vacuum valve and check valve(s). Also check for proper vacuum hose
routing. See Fig. 15.
Fig. 15: Typical Vacuum-Actuated EFE System
Courtesy of General Motors Corp.
EMISSION MAINTENANCE REMINDER LIGHT (EMR) (IF EQUIPPED)

If equipped, the EMR light (some models may use a reminder
flag) reminds vehicle operator that an emission system maintenance is
required. This indicator is activated after a predetermined
time/mileage.
When performing a smog check inspection, ensure EMR indicator
is not activated. On models using an EMR light, light should glow when
ignition switch is turned to ON position and should turn off when
engine is running.
If an EMR flag is present or an EMR light stays on with
engine running, fail vehicle and service or replace applicable
emission-related components. To reset an EMR indicator, refer to
appropriate MAINTENANCE REMINDER LIGHTS in the MAINTENANCE section.
MALFUNCTION INDICATOR LIGHT (MIL)
The Malfunction Indicator Light (MIL) is used to alert
vehicle operator that the computerized engine control system has
detected a malfunction (when it stays on all the time with engine
running). On some models, the MIL may also be used to display trouble
codes.
As a bulb and system check, malfunction indicator light will
glow when ignition switch is turned to ON position and engine is not
running. When engine is started, light should go out.

\003
EM IS SIO NS R EC ALL # 617 - O XYG EN S EN SO R & C AT. C O NV.

1 988 J e ep C hero ke e
EMISSION RECALL BULLETIN
EMISSIONS RECALL #617 - OXYGEN SENSOR AND CATALYTIC CONVERTER
Model(s): 1989 and 1990 Jeep Cherokee (XJ), Comanche (MJ) and\
Wrangler (YJ) Vehicles Equipped With a 2.5L Engine and
a Federal Emission Control System and Built After
November 27, 1988
Bulletin No.: 617
Date: May, 1995
NOTE: This is an Emission Recall bulletin.
VEHICLES AFFECTED
1989 and 1990 Jeep Cherokee (XJ), Comanche (MJ) and Wrangler (YJ)\
Vehicles Equipped With a 2.5L Engine and a Federal Emission Control
System and Built After November 27, 1988.
SERVICE INFORMATION
Failure of the oxygen sensor and catalytic converter on the listed
models, may cause a vehicle to be in violation of U.S Environmental
Protection Agency (EPA) Emissions Standards. To correct this
condition, the oxygen sensor and catalytic converter must be replaced
with improved design parts.
Details of this service action are explained in the following
sections.
SERVICE PROCEDURE VIDEOTAPE
No videotape of the service procedure for this recall will be
provided.
DEALER NOTIFICATION & VEHICLE LIST
INVOLVED DEALERS
Each dealer to whom involved vehicles were invoiced (or the current
dealer at the same street address) will receive a copy of this dealer
recall notification letter and a list of the involved vehicles by
first class mail.
The Vehicle List is arranged in Vehicle Identification Number (VIN)
sequence. Owners known to Chrysler are also listed. The lists are for
dealer reference in arranging for service of involved vehicles as
necessary.
ALL OTHER DEALERS
Each Jeep & Eagle dealer who does not receive a Vehicle List will
receive a copy of this dealer recall notification letter by first
class mail.
DIAL SYSTEM FUNCTION 70

All involved vehicles will be entered to DIAL System Function 70 at
the time of recall implementation for dealer inquiry by VIN as needed.
PARTS
IMPORTANT: A quantity of parts will be distributed initially and
billed to all involved dealers. This quantity will cover
a portion of the total vehicles involved. Additional parts
may be ordered as needed to support customer demand.
Each involved dealer, to whom vehicles in the recall were invoiced
(or the current dealer at the same street address), will receive
enough Emission Service Packages, Recall PN C3906170, to service 25%
of those vehicles.
Each parts package contains the following components:
EMISSION SERVICE PACKAGE







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Qty  Description  Qty  Description 






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1  Oxygen Sensor  1  Clamp 

1  Catalytic Converter  4  Bolts 

1  Gasket  4  Nuts 

1  Recall Completion Label  1  Instruction Sheet 










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OWNER NOTIFICATION & SERVICE SCHEDULING
All involved vehicle owners known to Chrysler are being notified of
the service requirement by first class mail. They are requested to
schedule appointments for the service with their dealers at the
earliest possible date. A copy of the
CUSTOMER NOTIFICATION LETTER is
in this bulletin.
Enclosed with each owner notification is an Owner Notification Form.
The involved vehicle and recall are identified on the form for owner
or dealer reference as needed.
SERVICE PROCEDURE
A. Replace Oxygen Sensor
1. Locate the oxygen sensor in the exhaust manifold as shown in
Fig. 1 .
2. Disconnect the oxygen sensor electrical connector.
3. Remove the oxygen sensor.
4. Clean the exhaust manifold threads using a thread chaser.
NOTE: Do not use solvents or lubricants on threads.
5. Install provided oxygen sensor. Tighten to 22 ft-lbs (30 N-m)
6. Connect oxygen sensor electrical connector.

Fig. 1: Oxygen Sensor Location
B. Replace Catalytic Converter
WARNING: IF TORCHES ARE USED WHEN WORKING ON THE EXHAUST SYSTEM,
DO NOT ALLOW THE FLAME NEAR THE FUEL LINES.
1. Remove and discard the nuts, bolts and gasket at the front of the
converter and the exhaust pipe clamp at the rear (see Fig. 2).
NOTE: Use penetrating oil if necessary.