Fuel gauge not reading correctly

[mudda_hunchie]

Hey guys.  I have a 70 charger.  I recently bought a new tank to install on the car. The fuel guage has never worked In The car.  I have a new sending unit that I bought years ago.  I checked the ohms on the sending unit installed in the car.  Reading was 86.9.  So I bought an aftermarket guage with ohm reading 0(E) and 90(F).  Hooked up the gauge and it immediately reads full with tank empty.  I returned that gauge and bought one with ohms 10(F) and 73(E).  Hooked this gauge up and it goes immediately to empty with an empty tank.  I added 5 gallons of gas and still shows empty. So I check Ohms on sender with the 5 gallons of gas in the tank.  Still reading 86.9.  Sender is grounded to the fuel line.  I don't even care if the guage is accurate.  I just need something to go by.  I was next going to add 5 more gallons of gas, but I don't think that is going to help.  When installed the sender, the arm moved freely inside the tank.  Do I have the wrong ohm gauge?  I'm out of ideas. 

[b5blue]

I use one of these with my 70 Charger new tank/sender and factory gauge,  https://www.google.com/search?client=firefox-b-1-d&q=Car+Fuel+Gauge+Interface+Module You adjust it to read as you like.

[DownZero]

Ground the sending unit and it should peg out the gauge.

[mudda_hunchie]

Fuel gauge module on order.

[b5blue]

  You have 5 known gallons in the tank? (A good start point.)

[mudda_hunchie]

Yessir. 5 known gallons in a brand new tank.  Only thing is I checked ohms at completely empty and they read 86.9.  Checked ohms again after adding the 5 gallons of gas, still 86.9.  This should have been lower after adding the fuel.  Thinking about adding 5 more gallons.  I'm running out of time to work on it.  Have a show approaching fast.  I just thought now would be the opportune time to work on it with the known value (5 gal) as you stated.

[b5blue]

Yup check connections and be certain it is installed correctly. Then adjust to read 1/4 tank, add 5gal and adjust to read 1/2. 

[70 sublime]

My sender and tank were brand new when I put them in my car
My gauge never read much more than half full when the tank was right full
I bought my parts 7 years ago
Some of the senders did not have the correct calabrations on them and that is how they acted
It might be a pain to do but can you get your sender out of the tank and wire it back up to the car and move the float all the way up to see if your dash gauge moves ?

If you are trying to get ready to go to a car event you can always just fill the tank right full and hope the gauge at least moves up to half like mine did so it would give you some idea or if it does not move at all you could keep an eye on the odometer and drive your car 50 miles and fill the tank again to get an idea that way how far you can go ( or carry a couple gallons in the trunk )

[histoy]

I've never had good luck with the new sending units reading accurately.  With the last few I've installed I've put 10 gallons in the tank, then adjusted the float arm so that the gauge reads 1/2 full.  It's not perfect, but it's close enough because I normally don't let my tank get much lower than that anyway.

[b5blue]

It is a hot mess. At least my adapter shows somewhat the tanks capacity.

[mudda_hunchie]

Got some more work to do (plus working for a living).  I'll try an update in a couple of days

[mudda_hunchie]

Got the Metermatch from Technoversion installed.  Started programming it. Just haven't finished yet.  At least the gauge is moving now.

[b5blue]