Stumped on Fuel Gauge

[Corts60]

Hi folks,

I used to think I was pretty decent at solving electrical gremlins, but this fuel gauge in my '86 is kicking my butt. It all started this summer when the gauge would only read 1/4 tank when it was full. This happened out of nowhere as it always worked before. It would move to E as you used fuel, i.e.: 1/8 tank would actually be 1/2 tank or so. I thought that was weird so I pulled the sender wire and put it directly to ground to test the gauge. That pegged the gauge out so I thought OK, bad sender.

I pulled the tank and replaced the sender. before I put the new sender in the tank, I hooked it up to the sender wire and ground and manually moved it and watched the gauge respond. OK, all good? Then I put the sender in the tank, installed the tank and added 6 gal of gas or so. The gauge will not come off of E. If I ground out the sender wire, It will peg full as before. I rechecked all grounds from sender to frame, frame to battery, battery to body, etc. All are 1ohm or less.

Any one have any ideas of what I am not doing correctly here?

Thanks in advance,

Cort