Help With Fuel Sender

[Carmambo]

I am replacing the gas tank and sender in my 1959 cadillac. The old tank and sender were a rusted mess (sitting in Calf for 22 years) my problem is that the sending both the old and the new sending units when brought to the emty position, the gage stops at a little above a quarter tank. When the arm is brought to the full position the gage will go to full or slightley above full.  When the key is shut off the gage comes to rest below emty.  even the old sending unit which is a rusted hulk acts the same way.  the new unit mesures 3.7-36.7 ohms  does anyone know if this is correct I cannot check it to the old one it has been pitched.  Could this be a gage problem, can I calibrate the system in some way?   HELP!

[Jeff Maltby 4194]

I can't help you with this question but when I owned my 59, I ran out of gas once with the gauge showing a 1/4 tank.  You can call the companys that make new tanks/sending units for their advice.

[J. Gomez]

The resistance of the sender is correct, these are 30 ohm systems. If your gauge is stuck on the mid range with the sender on-line it could be a defective gauge.

The gauge uses opposing resistance coils to direct the needle to either direction working in conjunction with the sender resistance. One of these coils maybe bad/open causing the needle to stay at the mid-range.

You will need to remove and test the gauge; the resistance across the two terminals would be approximately 83 ohms, from terminal “IGN” to ground 125-126 ohms, and from “SENDER” to ground 42 ohms.

Also make sure there is a good ground at the fuel tank and at the instrument cluster that could skew the readings.

Good luck..!

[mario]

hey jose:
before he removes the guage, could he not touch the sender lead to ground and see if the needle swings empty to full, or full to empty, don't remember which. if there is no needle movement then the guage is at fault.
ciao,
mario

[J. Gomez]

Mario,

The problem with that is by removing the sender (resistance to ground) the gauge will paged to above “Full”, and once power if off the gauge will return slowly back to “Empty”.

A 3 ohm from “Empty” should place the needle just at the “E” mark; once power is removed the needle should go down slightly from this mark.

Under normal conditions the addition of the 32 ohms resistance from the sender sets different resistance between the coils as a series and parallel circuits. If the resistance of the coils changed (burned or shorted winding) the gauge will be skew.

Since he is getting movement on the needle by sweeping the float from “E” to “F”, but the needle stays at the ¼ “F” mark when the sender is at the “E” that could indicate a change in resistance somewhere. Since the same behavior is present with either new or old sender, the only variable left is the gauge.  

HTH

[mario]

hey jose:
thank you for claryfing that!
ciao,
mario