1990 jeep cherokee fuel gauge

[BlueOval]

Hi can anyone tell me why my fuel gauge reads over full? on my 1990 jeep cherokee. I checked the wires at the sending unit and the only power there is the one for the fuel pump, there are three wires Black for ground beige for sending unit and pink w/black stripe for fuel pump. I tried the light tester behind the cluster and there is no power at the fuel gauge, so I jumped a wire from one power source to the beige wire. and that made the needle move a little more past full. So can anyone help me with some ideas please ! Brian p.s Im tired of guessing when Im going to run out!

 

[Saurian]

Hhhmmm... Now, I'm not all that savvy when it comes to the newer Jeeps, as I've not yet had the pleasure of dissecting one, but on an '86 Grand Wagoneer, the fuel gauge pegs out if the circuit is broken, I assume it would be the same on yours... I know that the oil pressure gauge will do the same thing if you unplug it. Conversely, if you short circuit it, the gauge will go to empty, so your best bet is to trace the wiring, because there's a very good chance you've got a loose connection, or broken wire somewhere between the sender and the gauge... Of course, the sender could have gone lousy too...

This is what the FSM has to say for a '00 XJ...
FUEL GAUGE SENDING UNIT
DESCRIPTION
The fuel gauge sending unit (fuel level sensor) is
attached to the side of the fuel pump module. The
sending unit consists of a float, an arm, and a variable
resistor track (card).
OPERATION
The fuel pump module has 4 different circuits
(wires). Two of these circuits are used for the fuel
gauge sending unit for fuel gauge operation, and for
certain OBD II emission requirements. The other 2
wires are used for electric fuel pump operation.
For Fuel Gauge Operation: A constant input
voltage source of about 12 volts (battery voltage) is
supplied to the resistor track on the fuel gauge sending
unit. This is fed directly from the Powertrain
Control Module (PCM). NOTE: For diagnostic purposes,
this 12V power source can only be verified
with the circuit opened (fuel pump module
electrical connector unplugged). With the connectors
plugged, output voltages will vary from
about.6 volts at FULL, to about 8.6 volts at
EMPTY (about 8.6 volts at EMPTY for Jeep
models, and about 7.0 volts at EMPTY for
Dodge Truck models). The resistor track is used to
vary the voltage (resistance) depending on fuel tank
float level. As fuel level increases, the float and arm
move up, which decreases voltage. As fuel level
decreases, the float and arm move down, which
increases voltage. The varied voltage signal is
returned back to the PCM through the sensor return
circuit.
Both of the electrical circuits between the fuel
gauge sending unit and the PCM are hard-wired (not
multi-plexed). After the voltage signal is sent from
the resistor track, and back to the PCM, the PCM
will interpret the resistance (voltage) data and send
a message across the multi-plex bus circuits to the
instrument panel cluster. Here it is translated into
the appropriate fuel gauge level reading. Refer to
Instrument Panel for additional information.

Hope some of this helps, with my brother's, it was a bad sending unit, and a faulty wiring job underneath the Jeep... Best of luck.

 

[dingus]

ick that sounds like a major headache... if i were you i'd just ignore the guage and judge the fuel level by the trip meter.