1956 Fuel Sending Unit

[gatech1956]

How do I access the fuel sending unit and where is the location? So my temp gauge needle shoots into position at the turn of the key. My fuel gauge needle lazily moves to about 1/4 and stops and while I drive and start moving it will creep to 1/2 or a little under that. I think I am getting incorrect readings, I went to the gas station and was filling up when the gauge read practically 1/8 but gas filled all the way up to the tube after 8 gallons, then I turned the key and the needle read a tad over 1/4. I think I am not grounding correctly at the sender. Any other tips is much appreciated.

[J. Gomez]

How do I access the fuel sending unit and where is the location? So my temp gauge needle shoots into position at the turn of the key. My fuel gauge needle lazily moves to about 1/4 and stops and while I drive and start moving it will creep to 1/2 or a little under that. I think I am getting incorrect readings, I went to the gas station and was filling up when the gauge read practically 1/8 but gas filled all the way up to the tube after 8 gallons, then I turned the key and the needle read a tad over 1/4. I think I am not grounding correctly at the sender. Any other tips is much appreciated.

The fuel sending unit is inside the gas tank, you can find the mounting plate at the rear of the tank about mid-way top half just behind the diff.

If you are getting those erratically readings I would first connect a temp wire from a good ground source directly to the plate and see if that corrects the reading at the gauge. The sending unit would need a good ground to get a correct reading and the only ground source for it is the metal fuel line.

If you still getting the same reading most likely the sending unit is bad. You will need to remove it from the tank and bench tested the resistance is from 0 (full) to 30 (empty) ohms through the full sweep.

One other issue is the gauge itself the mid-coil is connected to the metal case to ground at the instrument panel; this connection could be foul with corrosion it may need to be clean to get it back alive.

Good luck..! 

[gatech1956]

The fuel sending unit is inside the gas tank, you can find the mounting plate at the rear of the tank about mid-way top half just behind the diff.

If you are getting those erratically readings I would first connect a temp wire from a good ground source directly to the plate and see if that corrects the reading at the gauge. The sending unit would need a god ground to get a correct reading and the only ground source for it is the metal fuel line.

If you still getting the same reading most likely the sending unit is bad. You will need to remove it from the tank and bench tested the resistance is from 0 (full) to 30 (empty) ohms through the full sweep.

One other issue is the gauge itself the mid-coil is connected to the metal case to ground at the instrument panel; this connection could be foul with corrosion it may need to be clean to get it back alive.

Good luck..!

Sender has been replaced, probably only 1 year old now. So I will try to run a better ground for the sending unit. As for the gauge, I am guessing this requires removing the instrument cluster, correct?

[J. Gomez]

Sender has been replaced, probably only 1 year old now. So I will try to run a better ground for the sending unit. As for the gauge, I am guessing this requires removing the instrument cluster, correct?

Unfortunately yes it does, but do yourself a favor before tackling the instrument panel removal by checking the fuel gauge is working properly by removing the wire from the sender first. If the fuel gauge pegs pass the “F” mark the gauge is fine.

Good luck..!

[Jeff Rosansky CLC #28373]

I just ran a ground wire to the sending unit mounting screw. May work for you.
Jeff

[gatech1956]

I just ran a ground wire to the sending unit mounting screw. May work for you.
Jeff

Thanks for the tip, Jeff. I will try that.

[gatech1956]

Unfortunately yes it does, but do yourself a favor before tackling the instrument panel removal by checking the fuel gauge is working properly by removing the wire from the sender first. If the fuel gauge pegs pass the “F” mark the gauge is fine.

Good luck..!

I did as you said the needle went to "F" just like you said. Gauge is fine then  ...So bad ground. But just so I understand when these cars were new the wire was grounded to the fuel tank, correct? Would replacing the straps in the that support the tank help?

[walt chomosh #23510]

D,
  Like Jeff rose and many other Cadillac owners I ran a ground wire from one of the sender screws to a good ground. Changing the tank straps wouldn't help due to the insulators that are glued to the straps, thus isolating the tank from ground. Ground the sender....walt...tulsa,ok

[J. Gomez]

I did as you said the needle went to "F" just like you said. Gauge is fine then  ...So bad ground. But just so I understand when these cars were new the wire was grounded to the fuel tank, correct? Would replacing the straps in the that support the tank help?

Bingo, as Walt mention above..! 

The only path to ground for the tank/sender was the metal gas line but with age it loses the connection downstream.

The sending unit would need a good ground to get a correct reading and the only ground source for it is the metal fuel line.