The Fuel Gauge Lies!!! How to fix?

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Varment

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I am finally sick of dealing with a fuel guage that is telling me one thing when I know my tank has a completely different amount of fuel in it and I am stuck as to what is causing it...

My gauge works, but only for the first 6-8 gallons. For the first 4 gallons of use it stays pinged out above full and then it just steadily drops mile by mile and after about 6-8 gallons of use it is on empty. My problem is that I have a 13 gallon tank. I have a brand new sending unit, new wiring, and have made sure everything is getting the power it needs but I am just completely lost as to how I fix this issue.

Could it be the actual gauge busted even though it works from E to F? If so, what causes this and is it something that can be fixed or do I have to go ahead and start looking for a new fuel gauge.

Thanks,
Spencer

Car Spec: 1968 Plymouth Valiant 100; 13 gallon tank.
 
You can check the gauge, round up some "power resistors" at Radio Shack or an electronics supplier

The test resistances are

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

Before you suspect the gauge, I'd replace the voltage limiter (EDIT) with a quality electronic replacement

Also inspect and go over your cluster. Mine had multiple problems Connector pins at the pc board were broken, loose corroded.

The temp/ fuel gauge stud nuts were corroded. twist them loose/ tight several times to "scrub them clean, better yet, replace with star washers and 'real' nuts

While you are at it, make sure the ground from the pc board to the cluster housing, and from there put a separate new wire from the cluster to the column support behind

To test the sender, you now have the resistance values above, empty the tank, and check the sender resistance at empty (around 73 ohms)
 
Where is a good place to read up more on a test like that? Never heard of doing something like that and have no idea where to start...
 
Look around and get the electronic replacement for the instrument cluster voltage regulator. Goes in stock spot, no bi-metal strip to fail (and cook your gauges), and is much more accurate.

A few of the mopar vendors who advertise in the magazines have 'em, about $40 I believe
 
i would also check the sending unit as well to make sure you didnt get a bad one ive seen several lately at the local parts stores
 
Excellent! Thank you for all the helpful tips guys and definately for the website. I'll try to find some reviews on that and the price seems good so I'll probably try that out now!

Thanks again,
Spencer
 
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