Fuel Gauge Sending Unit; Fuel Injector Test; Service Procedures Fuel System Pressure Release Procedure; Fuel Tubes/Lines/Hoses And Clamps - Jeep Wrangler 1999 Electronic Service Manual

14 - 10 FUEL SYSTEM
DIAGNOSIS AND TESTING (Continued)
(18) Disconnect test leads from relay cavities
immediately after testing.

FUEL GAUGE SENDING UNIT

The fuel gauge sending unit contains a variable
resistor (track). As the float moves up or down, elec-
trical resistance will change. Refer to Group 8E,
Instrument Panel and Gauges for Fuel Gauge test-
ing. To test the gauge sending unit only, it must be
removed from vehicle. The unit is part of the fuel
pump module. Refer to Fuel Pump Module Removal/
Installation for procedures. Measure the resistance
across the sending unit terminals. With float in up
position, resistance should be 20 ohms. With float in
down position, resistance should be 270 ohms.

FUEL INJECTOR TEST

To perform a complete test of the fuel injectors and
their circuitry, refer to DRB scan tool and appropri-
ate Powertrain Diagnostics Procedures manual. To
test the injector only, refer to the following:
Disconnect the fuel injector wire harness connector
from the injector. Place an ohmmeter across the
injector electrical terminals.
should be approximately 12 ohms
(68°F).
Fig. 14 Fuel Injector Internal Components—Typical
SERVICE PROCEDURES
FUEL SYSTEM PRESSURE RELEASE
PROCEDURE
Use following procedure if fuel rail is or is
not equipped with fuel pressure test port.
(1) Remove fuel fill cap.
(2) The fuel filler tube contains a spring-loaded
flap (door) located below fuel fill cap. The flap is used
as a secondary way of sealing fuel tank if fuel fill cap
has not been properly tightened. It is part of EVAP
monitor system when vehicle is equipped with a
Resistance reading
1.2 ohms at 20°C
Leak Detection Pump (LDP). The vehicle may be
equipped with flap installed into fuel filler tube
even though vehicle is not equipped with LDP
and EVAP monitor system. Place a nonmetallic
object into fuel fill tube and press on flap to relieve
any tank pressure.
(3) Remove Fuel Pump relay from Power Distribu-
tion Center (PDC). For location of relay, refer to label
on underside of PDC cover.
(4) Start and run engine until it stalls.
(5) Attempt restarting engine until it will no
longer run.
(6) Turn ignition key to OFF position.
CAUTION: Steps 1, 2, 3 and 4 must be performed to
relieve high pressure fuel from within fuel rail. Do
not attempt to use following steps to relieve this
pressure as excessive fuel will be forced into a cyl-
inder chamber.
(7) Unplug connector from any injector.
(8) Attach one end of a jumper wire with alligator
clips (18 gauge or smaller) to either injector terminal.
(9) Connect other end of jumper wire to positive
side of battery.
(10) Connect one end of a second jumper wire to
remaining injector terminal.
CAUTION: Powering an injector for more than a few
seconds will permanently damage the injector.
(11) Momentarily touch other end of jumper wire
to negative terminal of battery for no more than a
few seconds.
(12) Place a rag or towel below fuel line quick-con-
nect fitting at fuel rail.
(13) Disconnect quick-connect fitting at fuel rail.
Refer to Quick-Connect Fittings in this section.
(14) Return fuel pump relay to PDC.
(15) One or more Diagnostic Trouble Codes (DTC's)
may have been stored in PCM memory due to fuel
pump relay removal. The DRB scan tool must be
used to erase a DTC. Refer to Group 25, Emission
Control System. See On-Board Diagnostics.

FUEL TUBES/LINES/HOSES AND CLAMPS

Also refer to the section on Quick-Connect Fittings.
WARNING: THE FUEL SYSTEM IS UNDER A CON-
STANT PRESSURE (EVEN WITH THE ENGINE OFF).
BEFORE SERVICING ANY FUEL SYSTEM HOSES,
FITTINGS OR LINES, THE FUEL SYSTEM PRES-
SURE MUST BE RELEASED. REFER TO THE FUEL
SYSTEM PRESSURE RELEASE PROCEDURE IN
THIS GROUP.
TJ