Have problem with sender unit,it sticks at quater full,gives false reading miles left,

The values differ in all types of cars. Older cars peg out at 90 ohms. Newer cars range between 0 and about 400 ohms. Dis-connect the connector at the sender. Ground the sender wire and the gage should read empty. un ground and it should read full. They use a ceramic resistor in the tank that usually go bad.

Fuel gauges are never precision instruments, but you can fix this to show at least empty when it's empty.
If you can't access the top of the fuel tank you need to drain and then remove the fuel tank and take out the fuel sender unit. Otherwise just remove the sender unit from the tank.
Hold the wire with the float on it firmly and bend the wire to raise the float slightly.
Replace the float and check the fuel gauge reading. Repeat the procedure until the gauge gives an acceptable reading.
That should stop you from running out of go juice before the gauge hits zero, but you might not have a completely full reading when you fill up. Live with it..

The fuel sending unit rod was bent during the instalation giving you the false readings. This is the thin metal rod that attaches the float to the sender.

hi it can really only be two things, first is the fuel sender on the pump inside the tank it could be stuffed or sticking causing a false reading, second it can also be a faulty fuel gauge on the dash.

The Fuel level FLOAT, in the tank is defective. Possible that it "holed", and has sunk to the bottom of the tank.
To check, separate the harness plug to the Tank sender unit, and ground the supply to a suitable place on the frame. The dash gauge should record "Full", therefore the sender unit is suspect.
regards. DT

take the sender unit out and check the float ,sounds like its full of petrol and not floating giving a reading of empty

Hello. Before getting involved in real repairs, dump a bottle of fuel injector cleaner in your fuel tank. It may clean your sending units enough to get them working again. The chances of success are only about 50%, but the cost is very low. Redline, Chevron, and others make good fuel injection cleaner.

Sounds like the sending unit is going out. The sending unit has a float that measures the fuel level. They can start sticking in different levels. It is more than likely located inside the fuel tank.

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

this is an old post so not sure if problem has been resolved ?? but if not ? from your symptoms it sounds like the fuel tank sender unit is faulty and unfortunately not servicable but not too expensive to diy a new unit for a quick confirmation it is sender ? remove the wire from sender unit then scratch /hold to good earth whilst ignition is turned on and fuel guage is read by assistant ? if guage goes to full ? sender is faulty hope this helps?