1965 Valiant 225 CID. When I fill up the gas tank it will register “full” but after about 50 miles it quickly goes down towards half and then to empty by 75 miles.
Previous owner put in a new tank and sending unit. I don’t know where to start looking.
Someone told me there should be a “ground strap” of some sort that goes between the two metal lines that come out of the sender. There wasn’t one there so I improvised one using two hose clamps, one each around each tube, with a wire connected between them but the gauge still doesn’t work correctly.
I hope someone can help me. I hate going by miles driven to determine when I need gas.

The new aftermarket sending units are JUNK.
Look around. Similar complaints all over about them. Many sell them but all are sourced from the same place. There's a place that sells something called a "meter match" that helps calibrate the junk sender.
My son has had 4 of them, all claim empty when they should be reading 1/2.

Well that's not good to hear. Does anyone have a link on how to test my sending unit and fix/adjust it so it reads properly?
Thank you.

Those senders are not junk, But they do not match the factory resistance scale.

With the Technoversions Meter Match installed between the Fuel sending unit wire and the feed to the fuel gauge you can calibrate it to work just fine.

Once you add the meter match and get the sender to send the proper resistance or perceived resistance to the gauge through the meter match it should work well. It is a hassle..
I am honestly glad anyone makes parts to fit our cars.

Here is an older write up on mine

Greg

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http://www.youtube.com/hyperpack

The ground strap needs to bridge across the short piece of fuel hose between the metal elbow coming out of the sender and the metal fuel line running forward along the floor of the car.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan, using my improvised “ground”, where I put a hose clamp on each metal tube with a wire attached to each of them, would that be a good enough ground? I don’t have an OEM one as it is missing.
If my improvised ground is sufficient, for now, then should I be looking at the sending unit as the reason my gauge is not working correctly?
Thanks.

Your improvised ground strap should work fine.

Greg

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http://www.youtube.com/hyperpack

Dan, then it looks like I either have a sending unit issue or a fuel gauge issue
Which do you recommend I start with?
Thanks

I recommend you start by systematically troubleshooting the parts and seeing if they work before you change anything. Get some precision resistors from Digi-Key or a 100 ohm variable resistor and a multimeter. Unplug the fuel sending unit and connect the resistor between the fuel sending unit and ground. The resistances to trigger the gauge should be:

10 ohms - full
23 ohms - middle
73-74 ohms - empty

You can also pull the sending unit out and check its range against these values with a multimeter.

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Matt Cramer
1966 Dodge Dart turbo / EFI project