Inaccurate fuel gauge

[Litchkar]

Surprise, my fuel gauge drops quickly after 3/4 of a tank. I have changed senders, and adjusted the float. Has anyone tried one of these ohm calibration boxes?

 

[Challenger RTA]

Maybe you need to get your foot off the throttle and it won't go down so quick!

 

[Challenger RTA]

Factory style sending unit? Ground strap on.

 

[Litchkar]

Maybe you need to get your foot off the throttle and it won't go down so quick!

Factory style sending unit? Ground strap on. View attachment 125034

Yes and yes, reads full but drops quickly to half tank. Takes 5 gallons to fill up to full when it reads half.

 

[Xcudame]

Maybe I'm just unlucky, but every Mopar I've owned seems to deplete the bottom half of the tank than the top half. I figured it was something to do with the resistance of how the gauge works, and the float sloshing around more in a half tank.

 

[Challenger RTA]

When I was driving 250 miles one way to the base. I would fill up and make it there and have above 1/8 of a tank left. It would take a whopping $8- 12 gallons to fill it back up. $12 if I was on it a bit. At 12 gallons fill up there is about 5 gallons left.
There always seemed to be more miles in the tank if I pushed it. The top always went quick.

 

[NixDad]

do you have a new, reproduction sending unit or an original?

 

[MoparCarGuy]

The factory gauge needs 5VDC to operate correctly. The factory Instrument Voltage Regulator (IVR) is bimetal mechanical (switched 12VDC contacts) and simulates a pulsed 5VDC. Not that accurate of a regulator and, if original, is probably in need of replacement. Consider the Real Time Engineering (RTE) IVR.

You should verify what voltage you are getting to the gauge when you have 10Ω (full tank reading near 5VDC), 31Ω (1/2 tank near 2.5VDC), and 73Ω (empty tank near 0VDC).
Your sending unit should be fairly consistent across its 63Ω range (10 to 73Ω) but many find the factory sending units to not be linear which causes the symptom you are having.