1988 JEEP CHEROKEE Service Repair Manual

Fig. 20: TEST 4A: SYSTEM OPERATIONAL (Cont.)

Fig. 21: TEST 4A: SYSTEM OPERATIONAL (Cont.)

Fig. 22: TEST 4A: SYSTEM OPERATIONAL (Cont.)

Fig. 23: TEST 5: BASIC ENGINE

Fig. 24: TEST 6: MANUAL TRANSMISSION UPSHIFT
WIRING DIAGRAMS

Fig. 25: Cherokee, Comanche & Wagoneer Throttle Body Fuel
Injection System Wiring Diagram

Fig. 26: Wrangler Throttle Body Fuel Injection System Wiring Diagram

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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.