fuel type JEEP CHEROKEE 1988 Service Repair Manual
[x] Cancel search | Manufacturer: JEEP, Model Year: 1988, Model line: CHEROKEE, Model: JEEP CHEROKEE 1988Pages: 1378, PDF Size: 19.9 MB
Page 21 of 1378
An electric in-tank fuel pump supplies fuel through the fuel
filter located under the right rear floor pan to the throttle body,
maintaining a constant operating pressure. Fuel enters the fuel bowl
reservoir of the throttle body through the injector and overflow type
fuel pressure regulator. The fuel pump is controlled by the ECU. A
ballast resistor attached to the right side of the plenum chamber,
reduces fuel pump speed after engine is running. The resistor is
by-passed in the "Start" position.
The fuel injector and fuel pressure regulator are integral
components of the throttle body. The injector is electronically-
controlled by the ECU. See Fig. 15.
Fig. 2: Cross Section View of Injector
The fuel pressure regulator is a diaphragm-operated relief
valve which maintains fuel pressure of 17.3 psi (1.2 kg/cm
). See
Fig. 16. Fuel in excess of this pressure is returned to fuel tank by a
Page 26 of 1378
MAT, MAP, EGO, speed and knock sensors. It also is informed of
throttle, gear (automatic transaxle models) and A/C control position.
When the ECU receives deceleration input from the closed
throttle (idle) switch, it grounds the EGR valve/canister purge
solenoid. This interrupts vacuum to EGR valve and canister purge
function. The injector is grounded, and during rapid deceleration,
the ECU may stop injection for a short period of time. The ECU also
controls engine idle speed and throttle stop angle.
WIDE OPEN THROTTLE MODE
During wide open throttle mode, the ECU receives inputs from
the CST, MAT, MAP, EGO, speed and knock sensors. It also monitors
throttle position.
When the ECU receives deceleration input from the closed
throttle (idle) switch, it grounds the EGR valve/canister purge
solenoid. This interrupts vacuum to EGR valve and canister purge
function. The EGO sensor input is not accepted by the ECU. The
injector is grounded and amount of fuel is precisely controlled.
IGNITION SWITCH "OFF" MODE
When ignition switch is turned "OFF", the ECU ceases to
provide ground for the injector and all fuel injection stops. The ECU
causes the idle speed actuator to fully extend for the next start up.
The ECU then deactivates.
COMPONENT TESTING
NOTE: When test calls for volt-ohmmeter, use of a high impedance
digital type is required.
Fig. 5: Diagnostic Connectors D1 and D2 Terminal Identification
1) Disconnect wiring harness connector from the MAT sensor.
Test resistance of the sensor with an ohmmeter. If resistance is not
185-100,700 ohms (3400 ohms at 70
F; 1600 ohms at 100 F), replace
Page 136 of 1378
Threads damaged ......... A .. Require repair or replacement.
Threads stripped (threads
missing) ............... A ............ Require replacement.
Wire lead conductors
exposed ................ B .. Require repair or replacement.
Wire lead corroded ...... A .. Require repair or replacement.
Wire lead open .......... A .. Require repair or replacement.
Wire lead shorted ....... A .. Require repair or replacement.
(1) - Refer to manufacturer's diagnostic trouble code
procedure and require repair or replacement of
affected component(s).
( 2) - Determine cause and correct prior to repair or
replacement of part.
( 3) - Determine source of contamination, such as engine coolant,
fuel, metal particles, or water. Require repair or
replacement. Check for accepted cleaning procedure.
( 4) - Inoperative includes intermittent operation or out of
OEM specification. Some components may be serviceable.
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COOLANT
COOLANT INSPECTION \
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Condition Code Procedure
Acidity (pH) incorrect .. 1 ........... Suggest correction or
replacement.
Contaminated ............ B ...... ( 1) Require replacement or
recycling. Further
inspection required.
Level incorrect ......... B .......... ( 2) Require filling to
proper level.
Maintenance intervals ... 3 ........ ( 3) Suggest replacement.
Mixture incorrect ....... B ........... Require correction or
replacement.
Type incorrect .......... B ............ Require replacement.
( 1) - Determine source of contamination and require correction
prior to coolant replacement.
( 2) - Determine source of incorrect level and suggest repair.
( 3) - The system should be drained and/or flushed and
refilled with correct coolant according to OEM
recommended service interval and procedures.
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COOLING FAN BLADES
COOLING FAN BLADE 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
of hardware.
Page 306 of 1378
NOTE: Copied Vehicle Speed Sensors from Engine UIGs & added
Air Gap incorrect, loose, and wire lead misrouted. For
"contaminated" removed coolant & fuel examples from note.
SPEED SENSOR INSPECTION
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Condition Code Procedure
Air gap incorrect ....... B ....... (1) Require adjustment or
replacement.
Attaching hardware
missing ................ C .......... Require replacement of
hardware.
Attaching hardware
threads damaged ........ A ... Require repair or replacement
of hardware.
Attaching hardware
threads stripped
(threads missing) ...... A .. Require repair or replacement
of hardware.
Connector broken ........ A .. Require repair or replacement.
Connector (Weatherpack
type) leaking ........... A .. Require repair or replacement.
Connector melted ........ A ........... ( 2) Require repair or
replacement.
Connector missing ....... C ............ Require replacement.
Contaminated ............ A ........... ( 3) Require repair or
replacement.
Inoperative ............. B ........... ( 4) Require repair or
replacement. Further
inspection required.
Lead routing incorrect .. B ..... Require rerouting according
to vehicle manufacturer's
specifications.
Leaking ................. A .. Require repair or replacement.
Loose ................... A .. Require repair or replacement.
Missing ................. C ............ Require replacement.
Resistance out of
specification .......... B .. Require repair or replacement.
Sensor housing cracked .. 2 ............ Suggest replacement.
Terminal broken ......... A .. Require repair or replacement.
Terminal burned,
affecting performance .. A ........... ( 2) 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.
Threads damaged ......... A .. Require repair or replacement.
Threads stripped
(threads missing) ...... A ............ Require replacement.
Wire lead conductors
exposed ................ B .. Require repair or replacement.
Wire lead corroded ...... A .. Require repair or replacement.
Wire lead misrouted ..... B . Require re-routing according to
vehicle manufacturer's
Page 346 of 1378
CO M PU TE R R ELE A R N P R O CED URES
1988 J e ep C hero ke e
GENERAL INFORMATION
Computer Relearn Procedures
All Models
* PLEASE READ THIS FIRST *
The following general procedures are to be used if
driveability problems are encountered after power loss or battery has
been disconnected. These procedures may provide an aid in eliminating
these problems.
To reduce the possibility of complaints, after any service
which requires battery power to be disconnected, vehicle should be
road tested.
COMPUTER RELEARN PROCEDURES
Vehicles equipped with engine or transmission computers may
require a relearn procedure after vehicle battery is disconnected.
Many vehicle computers memorize and store vehicle operation patterns
for optimum driveability and performance. When vehicle battery is
disconnected, this memory is lost. The computer will use default data
until new data from each key start is stored. As computer memorizes
vehicle operation for each new key start, driveability is restored.
Vehicle computers may memorize vehicles operation patterns for 40 of
more key starts.
Customers often complain of driveability problems during
relearn stage because vehicle acts differently then before being
serviced. Depending on type and make of vehicle and how it is
equipped, the following complaints (driveability problems) may exist:
* Harsh Or Poor Shift Quality
* Rough Or Unstable Idle
* Hesitation Or Stumble
* Rich Or Lean Running
* Poor Fuel Mileage
These symptoms and complaints should disappear after a number
of drive cycles have been memorized. To reduce the possibility of
complaints, after any service which requires battery power to be
disconnected, vehicle should be road tested. If a specific relearn
procedure is not available, the following procedure may be used:
Automatic Transmission
* Set parking brake, start engine in "P" or "N" position.
Warm-up vehicle to normal operating temperature or until
cooling fan cycles.
* Allow vehicle to idle for one minute in "N" position. Select
"D" and allow engine to idle for one minute.
* Accelerate at normal throttle position (20-50%) until vehicle
shifts into top gear.
* Cruise at light to medium throttle.
* Decelerate to a stop, allowing vehicle to downshift, and use
brakes normally.
* Process may be repeated as necessary.
Manual Transmission
Page 575 of 1378
Fig. 3: Typical Thermostatic Air Cleaner System
FUEL EVAPORATIVE SYSTEM (EVAP)
The EVAP system allows for proper fuel system ventilation
while preventing fuel vapors from reaching the atmosphere. This means
that vapors must be caught and stored while the engine is off, which
is when most fuel evaporation occurs. When the engine is started,
these fuel vapors can be removed from storage and burned. In most
systems, storage is provided by an activated charcoal (or carbon)
canister. See Fig. 4. On a few early systems, charcoal canisters are
not used. Instead, fuel vapors are vented into the PCV system and
stored inside the crankcase.
The main components of a fuel evaporation system are a sealed
fuel tank, a liquid-vapor separator and vent lines to a vapor-storing
canister filled with activated charcoal. The filler cap is normally
not vented to the atmosphere, but is fitted with a valve to allow both
pressure and vacuum relief.
Although a few variations do exist between manufacturers,
basic operation is the same for all systems. Check for presence of
vapor storage canister or crankcase storage connections when required.
Ensure required hoses, solenoids, etc., are present and connected
properly. Check for proper type fuel tank cap. Check for any non-OEM
or auxiliary fuel tanks for compliance and the required number of
evaporation canisters.
Page 576 of 1378
Fig. 4: Typical Fuel Evaporative System
CATALYTIC CONVERTERS
Oxidation Catalyst (OC)
This type of converter is the most common. It may use pellets
or monolith medium, depending upon application. See Fig. 5. Platinum
and palladium (or platinum alone) are used as catalyst in this type of\
converter.
Visually check for presence of catalytic converter(s). Check
for external damage such as severe dents, removed or damaged heat
shields, etc. Also check for pellets or pieces of converter in the
tailpipe.
Fig. 5: Typical Oxidation Catalytic Converter (Pellet Type) Shown;
Typical Three-Way Catalytic Converter Is Similar
Courtesy of General Motors Corp.
Three-Way Catalyst (TWC)
This type of converter is nearly identical to a conventional
Page 584 of 1378
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.
Page 586 of 1378
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)
Page 663 of 1378
Attaching hardware
threads stripped
(threads missing) ...... A ... Require repair or replacement
of hardware.
Connector broken ........ A .. Require repair or replacement.
Connector (Weatherpack
type) leaking .......... A .. Require repair or replacement.
Connector melted ........ A ........... (1) Require repair or
replacement.
Connector missing ....... C ............ Require replacement.
Contaminated ............ A ........... ( 2) Require repair or
replacement.
Inoperative ............. B ........... ( 3) Require repair or
replacement. Further
inspection required.
Leaking ................. A .. Require repair or replacement.
Missing ................. C ............ Require replacement.
Resistance out of
specification ........... B .. Require repair or replacement.
Restricted, affecting
performance ............ A .. Require repair or replacement.
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.
Threads damaged ......... A .. Require repair or replacement.
Threads stripped (threads
missing) ............... A ............ Require replacement.
Wire lead conductors
exposed ................ B .. Require repair or replacement.
Wire lead corroded ...... A .. Require repair or replacement.
Wire lead open .......... A .. Require repair or replacement.
Wire lead shorted ....... A .. Require repair or replacement.
( 1) - Determine cause and correct prior to repair or
replacement of part.
( 2) - Determine source of contamination, such as engine
coolant, fuel, metal particles, or water. Require
repair or replacement.
( 3) - Inoperative includes intermittent operation or out of OEM
specification. Some components may be serviceable; check
for accepted cleaning procedure.
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AIR CONDITIONING PRESSURE SENSORS
AIR CONDITIONING PRESSURE SENSOR INSPECTION \
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Condition Code Procedure
Attaching hardware
missing ................ C .......... Require replacement of
hardware.