Fuel gauge stuck on full

Yeah, quit trying to play auto mechanic an take it to a qualified repair shop. You have no clue how it works.

Fuel Gage Inaccurate or Inoperative (Buick)

Turn the ignition switch to the RUN position.
Using a scan tool, inspect for Powertrain Control Module (PCM) diagnostic trouble codes (DTCs). Refer to Engine Controls in order to diagnose PCM DTCs.
Turn the ignition switch to the OFF position.
Disconnect the fuel tank unit connector.
Connect the 2 red leads from the J 33431-C to the harness connector terminal B and terminal D.
Turn the ignition switch to the RUN position.
Set the tester resistance dials to 40 ohms (EMPTY).
Set the tester resistance dials to 248 ohms (FULL).
Does the fuel gauge display E at 40 ohms and F at 248 ohms?


Fuel Gauge (Buick, Pontiac)
The magnetic fields of the 2 coils move the fuel gauge pointer. The coils are at right angles to each other. The 2 coils are connected to each other. The fuel level Pulse-Width Modulated (PWM) circuit from the PCM connects at a middle point. Battery voltage is applied to the end of the coil at the E end. Ground is applied at the other coil's F end.
The fuel level sender resistance is proportional to the fuel level. The voltage across the sender is the fuel level input signal that is applied to the PCM on CKT 30 and CKT 452. The PCM provides a Pulse-Width Modulated (PWM) fuel level output signal on CKT 455 (PPL/WHT) to the instrument cluster fuel gauge.
When the tank is low, the fuel level sender resistance is low. A larger current passes through the E coil in order to move the pointer toward E on the scale. When the tank is full, the sender resistance is high. More current flows through the F coil. This moves the pointer toward F on the scale.
With 2 coils operating the pointer, the gauge is not affected by changes in the vehicle's electrical system.

Check fuse 4.

Chevrolet S-10 (1994-2004) fuses and relays

https://fuse-box.info > chevrolet > chevrolet-s-10-1994-...
1997 - Here you will find fuse box diagrams of Chevrolet S-10 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 and 2004, get information about the ...


Wiring diagram for the fuel pump

https://www.google.com/search?q=1997+chevy+s10+fuel+pump+wiring+diagram&rlz=1C1QJDB_enCA643CA644&sxsrf=AOaemvIE_tX-Fl6Z8Z0iSxCsRVwqrIdvZA:1635212709552&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjP8byF-ubzAhV2nWoFHeZQCyEQ_AUoAXoECAEQAw&biw=1920&bih=937&dpr=1

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If your fuel gauge is showing you in accurate readings this is normal to all vehicles that are not used to fill-up gas full regularly but sometimes the cause of the inacuracy is due to faulty float valve in the gas tank you need to replace it

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.
   

it is stuck io would put fuel cleaner in the tank and then i would if not i would replace it the floater is fowled up

{: ) A faulty fuel level sensor is most likely. But you must rule out first if theres' any problem with the gauge itself, like a stuck needle. A scan tool can command the cluster gauge to move at full sweep, effectively ruling out problem with the gauge. Without scan tool you can only approximate your judgement, like when you turn on your igniton, did the pointer move from fully down up to the Empty scale? Or did the needle never ever moved even a little?

There is something going on with the sending unit in the tank , sounds like the level sensor arm is stuck in the down position or has come off.
Hard to diagnose without physically seeing it.

Most of the time it is the Sending unit in the tank

pos lead is used to measure ground...that means that the power goes through the fuel level sending unit and the ground lowers the power out from the unit....I would replace the fuel level sending unit.

This is a normal concern.
The instrument cluster uses 4 different operating modes to calculate the fuel level:
Anti-slosh (default mode)
Key OFF fueling
Key ON fueling
Recovery
After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.
The default fuel gauge mode is called the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from empty (E) to full (F).
The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:
The key must be in the OFF position throughout the entire refueling of the vehicle.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 15 ohms ± 2 ohms and 160 ohms ± 4 ohms.
If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.
The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:
The transmission is in PARK (P).
The key is in the RUN position.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
In key ON fueling mode, a 30-second timer activates after the transmission is put into the PARK (P) position (automatic transmissions). When the 30-second time has elapsed and at least 15% of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transmission is shifted out of PARK (P), the fuel gauge strategy reverts to the anti-slosh mode. The key on refueling mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.
Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level input during a refueling event. Missing fuel level inputs result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:
The instrument cluster is in the anti-slosh (default) mode.
The actual fuel level in the tank is greater than what is being displayed by the fuel gauge