Fuel Gauge Issues

Jesse Martin said

Thanks for the info, I thought half tank would be 72-10÷2=32 ohms. I guess I'll pull the sender and check that.

Click to expand...

That is incorrect too. The range is 80-10. Calculator says half is 45 but... that's not how they work. I'll have to get a bit technical,,, The tank is not symmetrical so half of its volume is not half of the senders travel. As the nichrome winding inside a thermal gauge heats up, it's per inch/total resistance changes. This is why approx' 73 ohms will get up to the empty hash mark, then approx' 34 ohms signal is approx' 1/4, approx' 23 ohms signal is approx' half. Approx' 14 ohms is approx' 3/4. approx' 10 ohms is full. see how 1 ohm wouldn't make much difference in the cooler end of the range but that same 1 ohm would make noticeable difference in the hot end of the range? Anyway...
The aftermarket senders are linear ( like the calculator says ) so they do not work correctly. The meter match module suggested above does help correct it
Because the gauge needle goes up then falls back again, is see 2 separate problems. I want to ignore all the above for now and ask,,, New mechanical limiter or new solid state regulator?
A faulty mechanical limiter can produce the needle swings you have.