After buying $20 on 1/8th of a tank my gauge now reads full and then some.... Sending unit failure?

Make sure your gauge cluster and gas tank are properly grounded.

Ground for the gauge is a black wire coming off the fuel sender cap at the top of the tank to a screw into a rib on the bottom of the trunk foward of the tank. It's really close to where the tank strap connects.

Sender failures are usually when the tank reads empty all the time as the float has failed (and sinks to the tank bottom).

Where are those located dare I ask....

The wires are at the top middle of the tank next to where the fuel line goes into the tank.

The tank straps are at the left and right sides of the tank near the top (and the trunk floor).

If you have the OEM transverse muffler - fogetaboutit

Found the tank ground and it feels solid....

Next check the ground for the instrument cluster. Not sure where that is for a '69 - for '67/'68 it's the upper center dash carrier screw.

If those work out it could be the sender or the gauge. There are some troubleshooting suggestions around here someplace based on the electrical readings on a multi-tester.

Just read your original message again.

How many gallons did you put in? When my tank is full the gauge reads "super" full. All my GM products seem to do that.

full reads always past full on my 69....if everything is grounded and tight .its most likely the printed circuit....I had all kinds of problems until I replaced it...about $80 from Ames , way back 10-12 yrs ago...

Only put 5 gallons in and I know I was under 1/4. I dunno I'll drive it today and tomorrow to see if it moves. If no movement then I guess I get to go hunting....

Maybe the station overfilled my car and only billed me for $20..... Gosh that would be awesome. Never checked the total gallons since I was almost late to work.....

Then I would drive it some before checking to see if anything else is wrong. My gas gauge did the same thing 1st time I filled it completely.

My fuel gauge has done the exact same thing. I had filled the tank, the need went all the way to the right (more than ever before) and has never moved since. When the car is turned off it will move to the left a little but when the key is turned it will return all the way to the right. I have been told the same thing that the ground should be checked at the tank and when I did find it, it is buried behind the muffler lol. I think I might be able to get an extension in there to try and slightly unscrew and then srew the bolt back in to see if it will create a ground enough to see if that is the problem.

Otherwise it makes driving the car more exciting lol

PS - I do keep a very small 1/2 gallon fuel cell to get me out of trouble.

Thankfully after toggling the ignition on and off a few times I now have half a tank of gas. Score!

I have a similar problem. When I turn my headlights on, my fuel gage moves to the left like it is empty. When I turn headlight switch off, my fuel goes back to the right to the correct reading. This, I discovered just last night.

Definitely a ground problem for the instrument cluster. Been there, done that.

I had a similar problem last year just before parking the car for the winter. The last fill up the gauge pegged at full for a while, then suddenly worked right for a while. When I fired the car up in spring it was pegged angain and stayed there no matter what I did. Turned out to be the sending unit. If the coil on the sending unit goes bad the needle will read full. There is an easy way to test the gauge and curcuit board, open the wire between the sending unit and the dash board and short it to ground. If the gauge slowly goes to empty the wiring is good and the problem is either the sending unit or the ground. There is a connection inside the trunk, near the trunk latch, that you can seperate and ground to check it out.

Well my father in law is an electrical wizard so after we finish the 340 dart I'll play with my fuel system if need be.

WARNING: Electricity + fuel = BOOM!

^^^ are you sure?