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Re: 1985 t-bird, fuel gauge constantly reads full
I really doubt it is the fuel gage. You can test the gage by hooking a C cell battery to the wires from the tank. If it pegs the gage is good. You will need to go to Ford to get the sending unit. I doubt they will have this in stock, but they will order it for you. I would not even consider an aftermarket sending unit. Stick to the original Ford part. You will be happier with the results.
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TROUBLESHOOTINGPROBLEM: The fuel gauge does not work at all...no needle movement.
With the ignition switch on, remove the wire from the fuel tank sending unit and ground it to the unit housing. This removes the resistance supplied by the sending unit, and should cause the gauge to swing over to the 'Full' position. Does this happen?
The gauge and wiring are good. The problem is most likely with the sending unit. The sending unit must be removed for further testing. (1)
Ground the sending unit wiring to a good chassis ground (instead of the sending unit housing) and watch the gauge. Does it now peg out to the 'Full' side?
The problem is with the sending unit ground. Either the unit itself is bad or the float/arm is binding/missing. The sending unit must be removed for further testing.
The power supply to the gauge has been interrupted, (check fuses), the gauge is defective, or the wire from the gauge to the sending unit is open or has a break in it.
Testing the Sending Unit
After the sending unit has been removed from the tank, check to make sure the float is present, intact and still floats and that there is no binding with the float arm. Reconnect the gauge wiring to the unit and ground the unit. Move the float arm up and down. If the gauge reads full in the full up position and empty in the full down position, then the sending unit is good. Verify by hooking up an ohmmeter to it and making sure it reads 8-12 ohms full and 70-73 ohms empty. If not, the sending unit needs repaired or replaced. You can easily disassemble the head of the sending unit to clean and/or repair.
you have a float arm in the tank that rises when you add fuel I think its called the sending unit in the tank with fuel pump. it could be getting defective or it could be you fuel hand gauge going defective.but biggest part of time its the sending unit in the tank, hope this helps
Turn the ignition on and off several times before inspecting the gas tank because a blown fuse is the usual cause for fuel gauge malfunctioning. If the gauge remains motionless, check your fuse box and determine the fuse's location using your service manual. Replace the fuse if the link is broken or damaged. Then, inspect the gauge's wire connections for cleanliness and make sure the wires are connected. Turn the ignition switch to the "off" position. Attach one end of a jumper cable to the fuel-gauge terminal behind the gauge itself. Attach the other end to the ignition terminal. Replace the sender unit in the gas tank if the gauge reads full and your car does not have a full tank. Replace the fuel gauge if the needle remains inoperative.
Dont we wish it be full all the time but gas in it. Okay for the sending unit reading full its getting a full ground reading,Key on engine off. does it move and goe down. It should if it doesnt the problems with the gauge itself. 2 test disconnect the wire harness, did the gauge go down. the problem will be in the sending unit can be a hung float(Rare).
Sorry to say,but the fuel sending unit is the problem,the fuel tank will have to be lowered out of the vehicle to replace the unit.If the fuel sending unit is not available by itself you will have to replace the whole fuel pump assembley.
The problem most likely is not the gauge itself. It could be faulty wiring between the gauge & sending unit, or most likely a bad sending unit in the tank. Visit Ramchargercentral.com, do a thread search on fuel gauge issues, and you'll find a ton of info. If you need anything clarified, post up on the vehicle help board...the members there are happy to help!
My guess is it's the fuel sending unit which is in the fuel tank itself. A lot of vehicles sending unit is part of the fuel pump, if you're a pretty good mechanic, you can run the tank down really low, lower the fuel tank and replace the sending unit.
You don;t say whether the fuel gauge is reading accurately, or whether it's always on empty. If the gauge is always showing empty, it's most likely a problem with the sending unit in the fuel tank. Check the resistance across the two terminals of the sending unit.
On a C900, the fuel sender level unit is separate from the fuel pump
and located on the right side top of the tank, accessible by removing
the trunk floor lift up panel (the pump is located on the left side top
of the tank. Possible problems are: electrical line off or broken, float not working (it's fairly delicate); or gauge not working.
the resistance of the sending unit with the lines disconnected, the resistance should be
2.6 to 3.8 ohms full tank, 63.3 to 67.5 ohms empty tank; and test for
voltage across the top of the sender unit, if no voltage, that's likely
If the gauge is otherwise reading accurately (showing 'full' for a full tank, etc) then the problem is likely a gauge malfunction and can be simply replaced.