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Fuel guage calibration

Ralph

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So had my instrument guages rebuilt and calibrated by a professional while I was restoring my 73 cuda (non Rallye cluster). Several years ago.

All new fuel system lines, tank, sending unit, etc.

When full it reads about 1/2 tank and then on empty after 5 gallons usage. I know this cause that's what it takes to fill it up again.

My question: is there a calibration screw on the rearside of the fuel guage or do I need to remove the sending unit and bend the section that moves up and down to calibrate it.

Any help would be appreciated. just like to have it working correctly.

Thanks to all
 

fastmark

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Well it’s little more complicated than just that and it plagues lots of us. Take the sending unit out and ground it first then move the float while someone watches the gauge. If it does the same thing, then They just aren’t talking the same ohm reading. Some of these new sending units just don’t work with the old gauge. You can ohm the sender too. I’m sure someone can give you the proper ohms numbers. I decided it was my sending unit so I bought a product from tanks inc called a meter match. Check it out on the web. Itworks great.
 

NoCar340

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The resistance across the sender is 73 ohms when empty and 10 ohms full. Ground the wire at the tank directly to clean chassis metal somewhere not on the fuel tank or straps, and the gauge should go full scale, reading beyond the "F" mark, with the key in the "run" position. If it doesn't, your gauge is the problem. This test will not damage the gauge.

Before you start ripping things apart: Do you have the metal clip-on ground strap installed between the sender's outlet pipe and the body fuel line? The sender itself must be grounded directly to the chassis. It will not ground correctly through the fuel tank lock ring. On my car the factory clip-on strap wouldn't fit the new sender's huge ½" outlet pipe. I hose-clamped an ATC fuse tap--really just a glorifed male slide terminal--to the outlet pipe and ran a wire from it to an existing chassis fastener. The gauge works perfectly, even though the sender's just a cheap eBay replacement.
 

Ralph

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Got it. Will try it.

And yes it does have the ground strap installed
 

Cratos

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I had tried 2 new sender And nether would read right I new wiring added extra grounds dash was restored ( still have other issues there)
swapped out fuel tank for stealth fuel system gauge still not rightth getting ready to buy a new gauge :( .
 

70chall440

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I had tried 2 new sender And nether would read right I new wiring added extra grounds dash was restored ( still have other issues there)
swapped out fuel tank for stealth fuel system gauge still not rightth getting ready to buy a new gauge :( .
It might be that you need a new gauge, you know you can bench test all of this right? You don't have to install everything to find out.
 

Cudamerf

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Problem could also be the 12 volt to 5 volt regulator on the backside of your dash. If it's wiggy and fuel gauge is not getting proper voltage , your gauge will be off.
I replaced my old mechanical one in my 71 Cuda's rally dash with a new solid state unit.
 

NoCar340

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...dash was restored ( still have other issues there)
This statement leads me to believe that in your case, @Cudamerf is on the right track with the voltage limiter. Real-Time Engineering's solid-state constant 5V unit is an upgrade I highly recommend.

With the battery and gauge wiring disconnected, put jumper wires on the two terminals for the gauge. With the jumper wires connected to a good (preferably new) AA (or AAA, or C, or D) battery, you should get roughly a quarter-scale reading from the gauge's needle after several seconds. Be patient; the gauge circuitry is dampened so it takes a minute or so to read. Do not use anything other than a 1.5V battery for this.

The same test, with similar results, can be applied to the temperature and oil-pressure gauges as well. Do NOT attempt this test on your ammeter. It works differently. Its internal circuitry essentially presents a dead short to a battery. Things will get exciting quickly, and you may well need to replace the ammeter after your burns heal.

This is a test I just did on my known-good Rallye fuel gauge for illustration purposes:

100_3806.JPG
 

Huskidrive

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I had the same problem with 3 after market sending units. I had kept my 50 year old sending unit and, after I reinstalled it, my gauge is accurate to within 2 gallons. When the needle hits E and I top off the tank it takes 16 gallons....I'm happy
 

Cratos

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I have replaced the fuel system with an Aeromotive stealth system . so i guess ill replace the gauge and see when happens.
 

NoCar340

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I have replaced the fuel system with an Aeromotive stealth system . so i guess ill replace the gauge and see when happens.
Whatever you do, do not attempt to diagnose the actual problem. Ignore all of the diagnostic information posted in this thread. Just keep throwing more and more parts and money at it. That might fix it... eventually. 😂
 
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