1988 JEEP CHEROKEE ignition

Fig. 10: TEST 2: IGNITION ON: POWER (Cont.)

Fig. 11: TEST 3: IGNITION ON: INPUT

Fig. 12: TEST 3: IGNITION ON: INPUT (Cont.)

Fig. 13: TEST 3: IGNITION ON: INPUT (Cont.)

Fig. 14: TEST 3A: IGNITION ON: THROTTLE POSITION SENSOR (M/T)

\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.

1 - 25 Amp
Rear Washer/Wiper.
2 - 15 Amp
Radio, Cigarette Lighter.
3 - 25 Amp
Blower Motor.
4 - 20 Amp
Turn Signal, Back-Up Lights, Rear Window Defogger Relay.
5 - 10 Amp
Dome Light, Courtesy Lights, Glove Box Light, Cargo Light,
Radio Memory, Power Mirrors, Teltak Connector.
6 - 15 Amp
Hazard Warning System, Stoplights.
7 - 10 Amp
Parking Lights, Headlight Warning Chime/Buzzer, Instrument
Panel Light Dimmer.
8 - 7.5 Amp
Gauges, Instrument Cluster, Seat Belt Warning, Headlight
Delay, Chime Module, Overhead Console.
9 - 5 Amp
Instrument Panel Illumination.
10 - 25 Amp
Rear Window Defogger.
11 - 30 Amp (Circuit Breaker)
Power Door Locks, Power Seats, Trailer Towing Wiring Harness.
12 - 10 Amp
ETR Radio, Power Antenna.
13 - Not Used (1984-87); 7.5 Amp (1988)
Transmission Control Unit.
14 - 25 Amp
Headlight Delay, Horns, Security Alarm.
15 - 5.5 Amp (Circuit Breaker)
Front Wiper.
16 - 30 Amp (Circuit Breaker)
Power Windows.
17 - 10 Amp
Clock, Security Alarm (Ign).
CAUTIONS & WARNINGS
REPLACING BLOWN FUSES
Before replacing a blown fuse, remove ignition key, turn off
all lights and accessories to avoid damaging the electrical system. Be
sure to use fuse with the correct indicated amperage rating. The use
of an incorrect amperage rating fuse may result in a dangerous