Fuel gauge goes up when ignition is turned on, and then drops

I would initially suspect a bad ignition switch (not the lock....the actual switch). It could also be a short poor ground, failing component on the instrument cluster board etc. Try go ogling your problem with your specific year make and model to see if this may be a common issue.

Check cable which plugs into back of instrument cluster. Also fusible links.

• The temperature gauge is not on a fuse of its own, it would work with all the instruments, ie fuel gauge, warning lights etc. If the temp gauge does not work and the fuel gauge does,, look for the problem elsewhere such as the sender unit on the engine. A quick check is to remove the wire from the sensor unit on the engine and short it out to ground. If the gauge picks up, replace the sensor unit.
• Otherwise, check the wire itself for breaks, or bad connections.

The fuel level indicating system is a magnetic type system, which consists of the sending unit located in the fuel tank, an anti-slosh module located on the back of the instrument cluster, and a fuel gauge located in the instrument cluster. The sending unit changes resistance according to the level of fuel in the fuel tank, which varies the current flow through the gauge.The pointer position varies proportionately to the current flow. In this system, the sending unit resistance is low (22 ohms) when the fuel level is low and high( 145 ohms) when the fuel level is high. The pointer of the magnetic gauge remains in position when the ignition is turned to the Off position. On some models, an anti-slosh module is used to dampen out fluctuating fuel signals from the sender. Some vehicles are equipped with a low fuel warning indicator. The anti-slosh module will also actuate the low fuel indicator when the fuel level in the tank reaches 1/16 to 1/8 full.


Do your other gauges/warning indicators work properly with the ignition on? If not, check for power at the fuse panel/fuses.

If they do then partially remove your cluster with connector still installed and check for voltage at cluster connector and gauge. Check continuity of cluster and gauge for ground.

Sometimes the anti-slosh module (if installed) goes bad in the Grand Marquis but not likely.

Sender troubleshooting:

1. Perform test with resistors as follows:

1. Disconnect wiring connector at sender unit, then connect resistor between gauge lead and a suitable ground.
2. Turn ignition switch to On position.
3. With 145 ohm resistor, the gauge pointer should contact the Full mark.
4. With 22 ohm resistor, the gauge pointer should contact the Empty mark.

1. Perform test with fuel sender of known quality as follows:

1. Turn ignition to Off position.
2. Disconnect wiring connector from sender and connect it to test sender.
3. Move float rod away from fuel filter against Full stop position. Wait approximately 30 seconds, then turn ignition switch to On position. The gauge should read on or above the Full mark.
4. Move float rod toward fuel filter against Empty stop position. Turn ignition switch to Off position. Wait approximately 30 seconds, then turn ignition switch to On position. The gauge should read on or below the Empty mark. If gauge works properly replace sender, which involves dropping fuel tank.
   

2005 Instrument cluster layout

1. Speedometer
2. Brake warning light
3. Turn signal indicator light
4. High beam indicator light
5. Malfunction Indicator Light (MIL)
6. Airbag warning light
7. Anti-Lock brake warning light
8. Tachometer
9. Security alarm indicator light
10. Oil pressure warning light
11. Electronic Stability Program (ESP)/
Traction Control System (TCS) indicator light
12. Tire Pressure Monitor warning light (base)

13. Temperature gauge
14. Electronic Vehicle Information Display
15. Tow/Haul indicator light
16. 4WD Low mode indicator light
17. Seat belt reminder light
18. Cruise control indicator light
19. Odometer/Trip Odometer
20. Transmission gear indicator
21. Fuel gauge
22. Electronic Throttle warning light (5.7 Hemi)
23. Front fog light indicator light
24. Voltage warning light

Hi,

This solution will be of great help to you,even in the case of future or other dashboard problems;
Instrument cluster consists of electronic analog gauges, various warning lights, and optional tachometer. Vehicles equipped with tachometer have an electronic vacuum fluorescent transmission range indicator (PRND3L),odometer and trip odometer display. Vehicles without tachometer are equipped with a cable-operated transmission range indicator.
Instrument cluster is equipped with the following warning lights:
Battery voltage.
Cruise (speed control).
Door ajar.
Fasten seat belt.
Lift gate ajar.
Low fuel level.
Low windshield and washer level.
Traction Control.
The Body Control Module (BCM), which receives input from various sensors, sends display information to instrument cluster and operates gauges. Instrument cluster incorporates a self-test diagnostic feature to identify electronic problems. BCM, Powertrain Control Module (PCM), and Transmission Control Module (TCM) are continuously monitored by the diagnostic system.

SELF-DIAGNOSTICS
With ignition off, press and hold TRIP and RESET buttons while turning ignition switch to ON position. Continue to hold TRIP and RESET buttons until odometer window displays CODE (approximately 5 seconds). If problem exists, system will display diagnostic trouble codes. See DIAGNOSTIC CODE CHART table. If no problem exists, Code 999 (end test) will be displayed.
DIAGNOSTIC CODE CHART
CodeDescription
110.......Cluster Memory Fault
111.......Cluster Calibration Fault
905.......No CCD Bus Message From TCM
921.......Odometer Fault From BCM
940.......No CCD Bus Message From PCM

After diagnostic code display ends, instrument cluster will go into each of the following tests in order:
Dim test.
Calibration test.
Odometer segment test.
Electronic Transmission Range indicator segment test.
Dim Test
CHEC-0 will be displayed in odometer window. Instrument cluster will dim Vacuum Florescent (VF) display. If VF displays do not dim, a problem in instrument cluster exists. See BODY CONTROL COMPUTER TESTS in BODY CONTROL COMPUTER article.
Calibration Test
CHEC-1 will be displayed in odometer window. Each of instrument cluster gauges will move sequentially through each calibration point. See GAUGE CALIBRATIONS table. If gauge needle is not calibrated properly, a problem in instrument cluster exists.

Odometer Segment Test
CHEC-2 will be displayed in odometer window. Each segment of odometer will light sequentially. If any segment does not light, replace instrument cluster.
Electronic Transmission Range Indicator Segment Test
CHEC-3 will be displayed in odometer window. Each segment of electronic transmission range indicator will light sequentially. If any segment does not light, replace instrument cluster.

Sounds like possibly the ignition switch is going out. Try jiggling the key in the ignition in the on position and see if your lights come back on.

The fuse number is

#16 - 5 Amp (Tan)

Gauges & Indicator Lights: Low Oil Light, Low Washer Light, Service Reminder Light, Transmission Oil Light, Brake Warning Light, Anti-Lock Brake Warning Light, Fuel Pacer Light, 4WD Indicator Light, Malfunction Indicator Light, Warning Buzzer, Overdrive Switch (1992-93); Transmission Oil Temperature Lamp, 4WD Lamp, Overdrive Module Seat Belt Warning Buzzer
(1994-95).

there are 2 large terminal plugs with the wiring for all the instruments that are plugged into the back of that panel. make sure they are snug and in place. You reach in and under but it may easier to "simply" remove the cluster. 4 screws hold it in place accessible form underneath and with a long phillips screwdriver and lighting.

It could be the voltage regulator for your instrument cluster is the problem.