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Gas Gage Reading at lower point of sending unit opening

Eoth

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Mar 10, 2004
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Just replaced my sending unit in my stock tank and I am unsure what the reading should be. Currently there is gas in the tank but it is just below the sending unit opening. I am currently reading almost 3/4 of a tank. I would think that it would be more like 1/4 of a tank.
 

DirtDonk

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I don't think I've ever seen it tested or compared quite that way Eoth. But it's not a bad way actually, as it's pretty consistent.

But did you test the unit out of the tank, before you installed it? That's the usual recommendation here. That way you can see if it's going to be compatible with your wiring, or if it needs some friendly tweaks.

Connect it to the wiring, turn the key on and have someone watch the gauge while you run the sender through it's range of motion.
That's how I did mine, and how I found out that even the brand new factory units (I bought two from the dealer back in about '78 or so) read low on my gauge.

Took a little bending of the arm, tweaking of the stops, and I had it reading perfectly the way I wanted. Which was just above the line when full, and just below the line when sucking fumes.
When right on the empty line, I knew I had just a couple of gallons left to play with.
Because that's how my original units were reading, I ended up tweaking the originals and reusing them instead of the new ones.

It was a little tedious, because the dampened gauge does not move quickly when you run the float arm through it's paces.
And awkward as all get-out if doing it by yourself. But it can be done!

Was the original sender reading incorrectly? Or was it dead completely?

Paul
 
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Eoth

Eoth

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I tested it before install only to confirm that at the lowest point of its "sweep" it read empty and the highest point it read full. The previous unit was reading properly I only replaced it as a precaution to ensure that there was no restrictions for my FI fuel pump.
 
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Eoth

Eoth

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Ok... Still futzing with this dam sending unit... Gas gage reading 1/2 tank with a couple of gallons (like 2-3) in it. Doing some research and it appears that 1970-77 should be 10 ohms full and 80 ohms empty. However the 1966-69 are 0 ohms full and 65 ohms empty.
So... Does that mean that I am using a 70-77 sending unit on a 66-69 gage?
And if so, is my solution just to adjust the gage as described in this post?

http://classicbroncos.com/forums/showthread.php?t=110202
 

Rustytruck

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Do you have 2 gas tanks? If you do they need to have the same float resistance if you go adjusting the the gauge. My math tells me that the early float resistance at 1/4 tank would be 52.5 ohms and the later float resistance would put that just under 1/2 tank if you were to use the late model float setup. Can you adjust the float stops enough to adjust the newer float set up to have the proper early sweep resistance? Then you would have to adjust the float arm so it floats on the fuel at the right level for the amount of fuel in the tank. Tank capacities were all over the place in Bronco fuel tanks which will complicate these settings.

http://www.broncohio.com/tech/broncochart.html
 

Rustytruck

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The question I have is? Does the IVR read the same out put with the key on ACC or the engine running as the input voltage changes with the engine running.
 
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Eoth

Eoth

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One gas tank.... I replaced a perfectly functioning sending unit because the screen/filter was torn and it looked ugly....
The sweep of the new float is exactly the same as the old.
There is no difference between the gage needle between running and just powered on.
 

DirtDonk

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Well, if it all goes to hell in a hand basket, you could always put a new filter on the old sending unit.%)

That said, there's got to be a way to adjust the new unit to read properly with the gauge I would hope.
At least I've never seen one yet that wasn't tweakable to match.

Good luck.

Paul
 

Viperwolf1

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The sender resistance wire is wound in a logrythmic manner. 10 ohms full and 73 ohms empty. Half scale is about 23 ohms. You need to bend the float arm up to make the gauge reading go down to match the actual fuel level.
 
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Eoth

Eoth

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I understand that bending the arm "sweep range" should trick the gage to read in the right range, but isn't adjusting the gage itself easier than all the trial and error of bending the arm?
The following post seems to be the ticket but everyone seems to be content bending the float arm rather than adjusting the gage. The gage adjustment is described in this post:

http://classicbroncos.com/forums/sho...d.php?t=110202

And yes I should have just ordered a new filter (didn't know you could). And I have corrected that mistake.
 

DirtDonk

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As long as the newly adjusted gauge still follows along with the whole sweep of the sending unit, I can't think of any reason it would not work either way.
The sending unit is usually the first thing to adjust simply because it's the thing that's out and being replaced. Most don't take the instrument cluster out and separate the components, so the gauge adjustment does not usually come into play.
And since most of the time, messing with the sender gets you close enough, tweaking the gauge won't come up as often anyway.

So it's more of a circumstance thing, rather than a right or wrong thing for most of us.
But as far as that "right or wrong" thing is concerned, adjusting the instrument is probably done for a specific setting expected as a starting point with the gauge. Maybe adjusting it changes something in the way it sweeps and reads the sender's information? I don't know. Guess I'll have to read the thread you linked to.
Kind of like adjusting the steering gearbox preload during initial setup, then re-adjusting it later to compensate for wear. The first one is correct, but the second reason can cause more trouble. Maybe the gauge is nothing like that though?

I've had to adjust the IVR output as well, but since that effects all three gauges equally, it's only suitable if all are reading the same amount off of scale.

Very interesting discussion. Be interested in hearing your results.

Paul
 

DirtDonk

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Link doesn't work for me by the way.
I get a "file not found" message.

Paul
 
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Eoth

Eoth

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http://classicbroncos.com/forums/showthread.php?t=110202

I hear what you are saying... Just knowing how far off everything is, I know that I am going to have to do a lot of trial and error to get the bend correct. Seems to me that according to the post above its just a matter of filling it up once and setting the "full", then drain the tank and set "empty".
I'm sure it wont work out that easy but its a nice thought... Thanks again for all your input!!!
 
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