FUEL GAUGE ISSUE

[ILIKECARS53]

Having a problem with the fuel gauge in my 1952 Chevy.  When the key is off the gauge reads Empty.  When I turn the key to on the gauge reads Full.  Here is what I have done so far. Have disconnected sending unit wire from the gauge no change from above.  Have done a continuity test on the sending unit wire from one end to the other  and   no breaks in the wire.  I could only check to about 2-3 inches before the sending unit without removing the tank. I am thinking that it is the sending unit itself.  Any thoughts on this.

There are some other wiring issues that have to get sorted out  but going after this one first.

Thanks in advance for your help    Jim

[Bloo]

Short the sending unit wire to ground. Gauge should go to empty. If it doesn't, look further at the gauge.

 

If it does, either the sending unit is bad, or the tank isn't grounded. Try grounding the tank. If that doesn't help, the sending unit is bad.

[misterc9]

Does the instrument cluster have a good ground ? The gas gauge itself needs a ground to operate. The oil and temp gauge in that car are mechanical and wouldn't be affected by a bad ground. You could test the ohm reading between the sender wire and ground with it disconnected from the gauge You need the shop manual to get the specs for it.  If you short the sending wire to ground be careful and only do it for a second  as it could burn the gauge out. The tank sender never gives a full ground to the gauge wire. There is always some resistance.

Edited September 15, 2017 by misterc9 (see edit history)

[Friartuck]

2 hours ago, ILIKECARS53 said:

Have disconnected sending unit wire from the gauge no change from above.

I think this phrase is the clue. Check to make sure the gauge is well grounded. Since the needle movement is based on magnetic coils, they need a good reference.

[Bloo]

4 hours ago, misterc9 said:

Does the instrument cluster have a good ground ? The gas gauge itself needs a ground to operate. The oil and temp gauge in that car are mechanical and wouldn't be affected by a bad ground. You could test the ohm reading between the sender wire and ground with it disconnected from the gauge You need the shop manual to get the specs for it.  If you short the sending wire to ground be careful and only do it for a second  as it could burn the gauge out. The tank sender never gives a full ground to the gauge wire. There is always some resistance.

 

Not on a Chevy of that vintage. 0 ohms is empty and 30 ohms is full. You are right there is always some resistance. That makes it tough to get the needle all the way to "e".

[ILIKECARS53]

Thanks guys.  Will work on within the next day or so  and  let you know what happens.