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Author Topic: fuel sender unit and gauge not matching up.  (Read 93 times)

remingtongoose77

  • Single Axle Driver
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  • Posts: 21
fuel sender unit and gauge not matching up.
« on: July 20, 2018, 04:34:45 PM »
Hello,

This is a new thread with more data than my last one. I have a 1996 HD gas truck. I built my own custom gas tank and I am trying to use the stock sender unit to work with my stock dash board fuel guage.

Here is the issue:

Before I install all of this I want to proof it out, so I purchased a new sender unit and plugged it into the factory connector and when leaving the float arm all the way down it works and reads empty, but all the way up reads 3/8's of a tank. Weird I thought. In the middle reads right between empty and 3/8's.

So my empty is empty and my full is 3/8's full. The gauge and the arm track well together but the gauge won't go above 3/8's full. Another strange detail is if you leave it holding a fuel level for more than a few seconds it will drop the needle on the gauge to empty no matter what it happening with the float arm.

I'm not sure if this is an HD thing or what. I am not planning on using the rear tank. I tried swapping out a different gauge cluster and same thing, I also tried this with the stock sending unit that was in there and again, same thing.

Anyone that has an idea or experience please chime in.

ED-NY

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  • Location: Champlain, NY
Re: fuel sender unit and gauge not matching up.
« Reply #1 on: July 20, 2018, 05:41:24 PM »
We run into this when installing those adjustable sending units in hot rods. What I do is mock-up the tank dimensions (high/low) on a piece of cardboard then hold the sending unit approx where it would mount on the cardboard template.   With the ohm meter attached move the float thru it's high/low positions.

You will then get a visual to determine whether the float arm needs to be lengthened, shortened or bent.

0-ohm empty
45-ohms half tank
90 ohms full tank

ED-NY

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  • Location: Champlain, NY
Re: fuel sender unit and gauge not matching up.
« Reply #2 on: July 20, 2018, 05:56:43 PM »
Hook up an ohm meter to make sure the sending unit is accurate (power not needed).

What I did to test the dash gauge is install a 100 ohm adjustable Potentiometer in a case with clips, then I just by-pass the sending unit and with "key on" (power needed) adjust the fuel gauge manually to determine if gauge is accurate.
« Last Edit: July 25, 2018, 01:31:50 PM by ED-NY »

remingtongoose77

  • Single Axle Driver
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  • Posts: 21
Re: fuel sender unit and gauge not matching up.
« Reply #3 on: July 20, 2018, 07:22:10 PM »
I will give this a shot.

What I am thinking is my truck had dual tanks and I am only using the sending unit and pump power connector from the front (main) tank. I think the little black box on the drivers side frame rail is the brain for the gauge in the dash. When both floats are up the gauge is full, right now I only have one sending unit up and the other not hooked up. - a mystery but one worth figuring out.

Tomorrow I am going to dig deeper and try the set up I have going with both floats up, and see if the truck is trying to calculate my total gauge reading of fuel from both tanks or just the one.

Thank you for the help and I will let you know what I find out.

 


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