70cutty

My fuel gauge has been stuck on 3 o'clock for a while. Finally I decided to buy a new Spectra sending unit and install it.
Dropped the tank, connected the wires to the new unit and tested the it out of the tank, it works fine. Float moves freely and gauge reads the position of the float.
I install the unit in the tank, put the thank back in the car, filled it up with gas, fuel gauge is stuck on E.

Drop the tank again, ran new wires to ground and trunk, tested the unit again out of the tank with new wires, works fine, fuel gauge reads position of the float.
Install the unit, put the tank back in the car, filled it with gas, back to being stuck on E.

What could be the problem?

Any help would be much appreciated.

oldcutlass

What happens if you remove the sender wire, it should go past F. If you ground that wire it should go to E? Sounds like you have a short to ground in the sender wire.

70cutty

If I remove the sender wire, gauge goes past F to 3 o'clock position.
What's weird is that I tested it multiple times and it works fine out of the tank, once it's back in the tank it doesn't work. I don't know what could be causing the short.
I wonder if it's a bad sending unit, but why would it work fine out of the tank.

Guess I'm gonna have to pull the tank again.

oldcutlass

Is there a wire running from the sending unit stud to ground in addition to the sender wire to the gauge?

70cutty

Yes there are 2 connections on top. I connected the wires and tested the unit, before dropping it in the tank, it worked fine. Wires stated in the same position, I made sure nothing was touching. Drop it in the tank, it acts like it's shorting out.

Amazon is sending another sending unit out, I'l try my luck with the new one and see what happens.

oldcutlass

Let me know how it works out. The sender wire is definitely shorting to ground somehow.

Olds64

My guess is that the sending unit is shorting out against the underside of the body when you install the tank. I had this problem with the replacement sending unit it my 71 98. There was a threaded stud on top of the sending unit where the signal wire connected. Every time I installed the tank the stud would short against the body of the car. I had to modify the sending unit. Once I removed the threaded stud I didn't have any more problems.

Here's the thread in which I fought this defective sending unit. I give a synopsis in the last post:

https://classicoldsmobile.com/forums...1971-98-a.html

70cutty

Thank you. Iv'e read the thread and sounds like I have the same problem you've had.

I'm gonna try to pull the tank tomorrow, I'll let you guys know how it works out.