I have a 2003 vw polo 1.4 hatchback. problem iks that the fuel gauge reads in reverse i.e when full it reads empty and vice versa. i have tried interchanging the blue and black wires on the fuel sende

When replacing the fuel pump housing in the tank of your 1999 Volkswagen Polo Playa 1.6i, the position of the housing is important. The fuel pump housing should be installed with the electrical plug on the top side of the housing. This is important because the plug is used to connect the fuel pump to the vehicle's electrical system and is necessary for the fuel gauge to function properly.
If the fuel gauge is working in reverse, it is possible that the plug on top of the fuel housing is connected in reverse or there may be a problem with the fuel gauge itself. Double check that the plug is connected correctly and make sure there are no loose connections.
If the problem persists after checking the plug, you may need to have the fuel gauge tested or replaced by a qualified mechanic or technician.

possible damaged during work --wiring disconnected or damaged --inserted wrong or jammed when reinserted

Have you tried reversing the wires? Does the gauge go up when using fuel?

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.
   

I have the same vehicle and my car actually was full of gas, registered empty & left me on the side of the road..It was the sensor in the fuel line that had to be replaced.

expensive- the sending unit- cheap- check for good ground at tank and for good wiring at tank

the fuel level sensor in the fuel tank is faulty the tank will have to removed to access it

Two possible problems.... the temp gauge wire is a single green wire attatched to the driver's side head (no1 bank) near the front in the side (in front of plug #1) ground it and your gauge should go to full hot,,, same with the fuel gauge, if you unplug it at the tank it should go to empty, or visa versa... if the gauges respond, replace the sending units, if they don't, replave the instrument panel

that's...thirty liters or so?...10.4 liters per hundred. I'm getting 30 UK MPG...that sounds rather low for a 1.2 . it should be getting 35-40, I believe. better get yourself a tuneup if you can afford it.

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