1988 JEEP CHEROKEE battery

See FUEL INJECTOR TEST PROCEDURE chart in this article.
REMOVAL & INSTALLATION
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Drain cooling system. Remove air cleaner assembly.
Disconnect CTS wire connector. Remove CTS from engine block. Install
replacement CTS and connect CTS wire connector. Install air cleaner
assembly. Fill cooling system.
OXYGEN SENSOR
Removal & Installation
Raise and support vehicle. Disconnect O2 sensor wire
connector. Remove O2 sensor from exhaust manifold. Install O2 sensor
and tighten to 30 ft. lbs. (41 N.m). Connect O2 sensor wire connector
and lower vehicle.
KNOCK SENSOR
Removal & Installation
Raise and support vehicle. Disconnect knock sensor wire
connector. Remove knock sensor from cylinder block. Install knock
sensor and connect knock sensor wire connector. Lower vehicle.
SPEED SENSOR
Removal & Installation
Disconnect speed sensor wire connector. Remove 2 speed
sensor retaining bolts at transmission housing. Install speed sensor
and connect speed sensor wire connector.
STARTER MOTOR RELAY
Removal & Installation
Disconnect negative battery cable. Identify, tag and
disconnect wiring to relay. Remove relay retaining screws and remove
relay from inner fender panel. Install replacement relay and connect
relay wires. Connect negative battery cable. Test relay operation.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
Removal & Installation
Disconnect wire connector from MAT sensor. Remove MAT sensor
from intake manifold. To install, reverse removal procedure.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal & Installation
Disconnect wire connector, vacuum hose, and retaining nuts
from MAP sensor. Remove sensor from firewall. To install, reverse
removal procedure.
FUEL INJECTOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.

Disconnect solenoid vacuum hoses. Disconnect solenoid wiring
connector. Remove solenoid retaining bolts and solenoid. To install
valve, reverse removal procedure.
ECU CONNECTOR PIN IDENTIFICATION 24-PIN CONNECTOR MPFI TABLE
\
\
\
\
\
\
\

Terminal No. Wire Function
A1 .................................................. Injector No. 3
A2 .................................................. Injector No. 6
A3 .................................................. Injector No. 2
A4 .................................................. Injector No. 4
A5 ................................................. Fuel Pump Relay
A6 ........................................................ Not Used
A7 ............................................. Oxygen Sensor Relay
A8 ..................................................... Shift Light
A9 ..................................................... Latch Relay
A10 ............................................. EGR/Evap. Solenoid
A11 ....................................................... Not Used
A12 ...................................................... A/C Relay
B1 .................................................. Injector No. 1
B2 .................................................. Injector No. 5
B3 ........................................................... AIS A
B4 .......................................................... AIS A1
B5 ........................................................... AIS C
B6 .......................................................... AIS C1
B7 .................................................. Battery (Pos.)\
B8 ........................................................ Ignition
B9 ........................................................ Not Used
B10 ............................................... Latched B (Pos.)\
B11 ......................................................... Ground
B12 ......................................................... Ground
\
\
\
\
\
\
\

Fig. 9: Multi-Point Injection ECU Connector
Courtesy of Chrysler Motors.
ECU CONNECTOR PIN IDENTIFICATION 32-PIN CONNECTOR MPFI TABLE
\
\
\
\
\
\
\

Terminal No. Wire Function
C1 ............................................. Speed Sensor (Pos.)\
C2 ..................................................... A/C Request
C3 ........................................................... Start
C4 ...................................................... P/N Switch
C5 .................................................... Sync. (Neg.)\

\003
FU EL IN JE C TIO N S YSTE M - T B I

1 988 J e ep C hero ke e
1988 Electronic Fuel Injection
JEEP/RENIX THROTTLE BODY INJECTION
2.5L Cherokee, Comanche, Wagoneer, Wrangler
DESCRIPTION
The Throttle Body Injection (TBI) system is a single
injector system that introduces fuel into throttle body from above
throttle plate. Fuel injector, located within throttle body, is
controlled by the Electronic Control Unit (ECU).
The ECU is a sealed microprocessor that receives input
signals from several sensors and other related engine components.
Based on these inputs, ECU generates output signals that control and
adjust air/fuel mixture and ignition timing as necessary for proper
engine performance.
ECU also controls engine idle speed, emission control
systems, upshift indicator light (manual transmission only), and A/C
compressor clutch.
OPERATION
ELECTRONIC CONTROL UNIT (ECU)
On Cherokee, Comanche and Wagoneer, ECU is located under
instrument panel, above accelerator pedal. On Wrangler, ECU is
located behind glove box. Input information from various engine
sensors to ECU is used to determine engine operating conditions and
needs. Battery voltage input is used to ensure that correct output
voltage is supplied by ECU during fluctuations in battery voltage.
FUEL INJECTOR
Fuel injector is mounted in throttle body so that fuel is
injected into incoming airflow. When injector solenoid is energized,
armature and plunger move upward against spring. Check ball above
injector nozzle moves off seat and opens small orifice at end of
injector.
Fuel supplied to injector is forced around ball and through
orifice, resulting in fine spray of fuel. Volume of fuel injected is
dependent only on length of time that injector is energized by ECU,
as fuel pressure is constant at injector. During cold engine starts,
extra fuel is supplied so richer mixture will aid in starting.
FUEL PRESSURE REGULATOR
Fuel pressure regulator is integral part of throttle body.
Pressure regulator has a spring chamber that is vented to same
pressure as tip of injector. Because differential pressure between
injector nozzle and spring chamber is same, only the length of time
that injector is energized controls volume of fuel injected.
Fuel pump delivers more fuel than is required by engine.
Excess fuel goes to fuel tank from pressure regulator via fuel return
hose. Fuel pressure regulator function is mechanical and ECU does not
control it.
FUEL PUMP

Electric roller type fuel pump is located in fuel tank.
Integral check valve is used to maintain pressure in fuel delivery
system after pump stops running. Fuel pump operation is controlled by
ECU through a fuel pump relay.
IDLE SPEED ACTUATOR (ISA) MOTOR
ISA motor acts as movable idle stop to change throttle stop
angle. Both engine idle speed and deceleration throttle stop angle
are set by ISA. ECU controls ISA motor by providing appropriate
voltage outputs to produce idle speed or throttle stop angle required
for engine operating condition.
OXYGEN (O2) SENSOR
Oxygen sensor is equipped with a heating element that keeps
sensor at proper operating temperature at all times. Oxygen sensor is
located in exhaust pipe.
Maintaining proper sensor temperature at all times, system
enters "Closed Loop" operation sooner and remains in "Closed Loop"
during periods of extended idle. Electrical feed to oxygen sensor is
through ignition switch.
The ECU receives sensor voltage signal which varies with
oxygen content in exhaust gas. Signal is used by ECU as reference for
setting air/fuel mixture ratio. ECU varies voltage to injector both
to compensate for battery voltage fluctuations and to change duration
of injector opening for control of air/fuel mixture.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
MAT sensor provides a signal to ECU that changes depending
upon temperature of air/fuel mixture in intake manifold. During high
temperature conditions, ECU will compensate for changes in density of
air.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
MAP sensor measures absolute pressure in intake manifold.
Both mixture density and ambient barometric pressure are supplied to
ECU by MAP sensor. Sensor is mounted in middle of firewall in engine
compartment. Sensor receives manifold pressure information through
vacuum line from throttle body. See Fig. 1.
Fig. 1: Manifold Absolute Pressure (MAP) Sensor
Courtesy of Chrysler Motors.
COOLANT TEMPERATURE SENSOR (CTS)

ECU receives inputs from A/C when either A/C switch is in
"ON" position or compressor clutch engages to lower temperature. ECU
changes engine idle speed depending upon A/C compressor operation.
POWER STEERING PRESSURE SWITCH
ECU receives input from pressure switch during periods of
high pump load and low engine RPM. Input signals from pressure switch
to ECU are routed through A/C request and A/C select input circuits.
When pump pressure exceeds 250-300 psi (17.5-21.0 kg/cm
), switch
contacts close transmitting an input signal to ECU. ECU raises engine
idle speed immediately after receiving input from pressure switch.
RELAYS
Starter Motor Relay
Starter motor relay provides an input signal to ECU when
starter motor is engaged.
System Power Relay
System power relay, located on right fender inner panel, is
energized when engine is started. It remains energized for 3 to 5
seconds after ignition is off. This allows ECU to extend ISA for next
start before ECU shuts down.
Fuel Pump Control Relay
Fuel pump control relay is located on right fender inner
panel. Battery voltage is supplied to relay from ignition switch.
When ground is provided by ECU, relay becomes energized and provides
voltage to fuel pump.
A/C Compressor Clutch Relay
ECU controls A/C compressor clutch through this relay. The
A/C compressor clutch relay is located beside fuel pump control relay
on right fender inner panel.
EGR Valve/Canister Purge Solenoid
Vacuum to both EGR valve and vapor canister is controlled by
this solenoid. When solenoid is energized, neither EGR valve nor
vapor canister receive vacuum.
Solenoid is energized during closed (idle) and wide open
throttle operations, engine warm-up and rapid acceleration or
deceleration. If solenoid wire connector is disconnected, both EGR
valve and vapor canister will receive vacuum at all times.
Load Swap Relay
The load swap relay works in conjunction with power steering
switch to disengage A/C compressor clutch. If compressor clutch is
engaged when power steering pressure switch contacts close, input
signal from switch to ECU also activates load swap relay. Relay then
cuts off current to A/C compressor clutch.
The A/C compressor clutch remains disengaged until pressure
switch contacts reopen and engine idle returns to normal. The load
swap relay contains a timer that delays engaging the compressor
clutch for 0.5 second to ensure smooth engagement.
ADJUSTMENTS
CAUTION: When working on or near engine that is running, be very
careful to avoid pulleys, belts and fan. DO NOT stand in
direct line with blades of fan. DO NOT wear clothing that is
loose enough to get caught in moving parts.

3) Return throttle plate to closed throttle position (M/T),
or maintain throttle plate in closed position (A/T). Check sensor
output voltage. To do so, disconnect voltmeter positive lead from
terminal "C" and connect it to terminal "A" (top) of sensor (M/T), o\
r
from terminal "A" and connect it to terminal "B" (A/T).
4) Move and hold throttle plate in wide open throttle
position (M/T), or maintain throttle plate in closed position (A/T).\
Ensure throttle linkage contacts stop. Note voltmeter reading. Output
voltage should be 4.6-4.7 volts (M/T), or .2 volt (A/T).
5) If output voltage is incorrect, loosen bottom sensor
retaining screw and pivot sensor in adjustment slot for a coarse
adjustment. Loosen top sensor retaining screw for fine adjustments.
Tighten screws after adjustment.
TESTING & TROUBLE SHOOTING
PRELIMINARY CHECKS & PRECAUTIONS
Subsystem Checks
Before testing fuel injection system for cause of
malfunction, check that following subsystems and components are in
good operating condition:
* Battery and charging system.
* Engine state of tune.
* Emission control devices.
* Fuel system pressure and delivery volume.
* Wiring connectors at components.
General Precautions
In order to prevent injury to operator or damage to system
or component parts, use following techniques:
* Turn ignition off before connecting or disconnecting any
component parts.
* DO NOT apply DC voltage greater than 12 volts or any AC voltage
to system.
* Disconnect battery cables before charging.
* Remove ECU from vehicle if ambient temperature could exceed
176

F (80
C).
* DO NOT modify or circumvent any system functions.
RESISTANCE & VOLTAGE TESTS
MAT Sensor
1) Disconnect wiring from MAT sensor. Using high input
impedance digital volt-ohmmeter (DVOM), check resistance of sensor.
Resistance should be less than 1000 ohms when engine is warm. Replace
sensor if it does not fall within range shown in
TEMPERATURE-TO-RESISTANCE VALUES table.
2) Test resistance in wiring harness between ECU connector
terminal No. 32 and sensor connector terminal. Also test resistance
in wiring harness between ECU harness terminal No. 14 and sensor
connector terminal. See Fig. 5. Repair wiring harness if open circuit
or resistance greater than one ohm is indicated.
Coolant Temperature Sensor (CTS)
1) Disconnect wiring harness from CTS. Using high input
impedance digital volt-ohmmeter (DVOM), check resistance of sensor.
Resistance should be less than 1000 ohms when engine is warm. Replace
sensor if it does not fall within range shown in
TEMPERATURE-to-RESISTANCE VALUES table.

\003
FU EL P U M P - E LE C TR IC

1988 J e ep C hero ke e
1988 Electric Fuel Pump
JEEP
2.5L TBI, 4.0L MPFI
DESCRIPTION & OPERATION
Fuel system on 2.5L TBI models operate under constant fuel
pressure of 14.5 psi (1.02 kg/cm). Fuel pressure regulator is
mounted on throttle body assembly. Excess fuel pressure is returned
to fuel tank. ECU has no control over fuel pressure relief valve.
Fuel pump is immersible type with permanent magnet electric motor.
A frame mounted in-line fuel filter is used. Fuel pump is
attached to fuel gauge sending unit in fuel tank. Voltage to operate
pump is controlled by Electronic Control Unit (ECU). A ballast
resistor is used in the fuel pump control circuit.
Ballast resistor is by-passed during start mode. During
running mode, ballast resistor reduces speed of pump by lowering pump
voltage. This ensures normal speed in running mode. The 1-ohm ballast
resistor is mounted on right side of plenum chamber.
Fuel pump control relay is located on front of right strut
tower. Battery voltage is supplied to relay from ignition switch.
Relay is energized when ECU provides a circuit to ground.
A multi-cell, roller type pump is used on all 4.0L MPFI
models. Pump and fuel filter are located on a plate, forward of rear
axle. Fuel pump control relay location for 4.0L models is on right
inner front fenderwell. Battery voltage is supplied to relay from
ignition switch. Relay is energized when ECU provides a circuit to
ground.
Pump contains 2 check valves. One valve relieves internal
pump pressure and regulates maximum pump output. Second valve,
located near pump outlet, restricts fuel movement in either direction
when pump is not in operation. System operates under a constant fuel
pressure of 31 psi (2.17 kg/cm
).
Fig. 1: 2.5L Fuel Pump & Fuel Gauge Sending Unit
Courtesy of Chrysler Motors.

2.5L TBI
1) Adjustment of fuel pressure is required after replacement
of pressure regulator. Remove air inlet from throttle body. Connect
tachometer to diagnostic connector terminals D1-1 and D1-3. Connect
fuel pressure gauge to fuel body pressure test fitting.
NOTE: Some TBI models do not have a pressure test fitting on
throttle body. Use Fitting (PN 8983 501 572) for this
purpose.
2) Start engine and accelerate to 2000 RPM. Turn adjustment
screw to obtain 14.5 psi (1.02 kg/cm
) fuel pressure. Location of
adjustment screw is on bottom of regulator. Install lead seal ball to
cover regulator adjustment screw after adjusting fuel pressure to
specification. Turn ignition off. Disconnect fuel pressure gauge.
Install cap on test fitting. Install air inlet.
NOTE: To increase fuel pressure, turn adjustment screw inward. To
decrease fuel pressure, turn adjustment screw outward.
4.0L MPFI
1) Remove cap from pressure test port in fuel rail. Connect
Fuel Pressure Gauge (J-37730-1) to pressure fitting. Start vehicle.
Pressure should be approximately 31 psi (2.7 kg/cm
) with vacuum
hose connected to pressure regulator.
2) Pressure should be 39 psi (2.74 kg/cm
) with vacuum
hose removed from regulator. If fuel pressure is not to
specifications, check for kinks or restricting bends in fuel supply
and return lines. Check fuel pump flow rate. Pump should deliver
minimum of 1.06 quarts (one liter) of fuel per minute with fuel
return line pinched off.
3) If flow is inadequate, check system for plugged fuel
filter or filter sock. Fuel pump flow rate can be checked by
connecting a hose to fuel test port on fuel rail and inserting other
end in clean container.
4) To operate fuel pump, install a jumper wire into
diagnostic connector terminals D1-5 and D1-6. Pinch off fuel return
line to ensure that no fuel returns to fuel tank. If fuel pressure is
still not to specifications and fuel flow is normal, replace
regulator.
REMOVAL & INSTALLATION
FUEL PUMP
Removal (2.5L TBI)
1) Disconnect battery cables. Ensure fuel level is less than
1/2 for this procedure. Remove fuel outlet and return hoses. Remove
sending unit wires. Remove sending unit retaining lock ring.
2) Remove sending unit/pump assembly with "O" ring seal.
Disconnect fuel hose from fuel pump. Disconnect wires from fuel pump.
Remove fuel pump from sending unit.
Installation
Clean seal contact are of fuel tank. Install new "O" ring
seal. Install a new filter on end of suction tube. Position sending
unit/pump assembly in tank. To complete installation, reverse removal
procedure. Start engine and check for leaks.
CAUTION: Fuel leaks can develop from over tightening sending
unit/pump during installation.