I am having trouble getting my fuel sensor and my fuel gauge to work together. With both the sender and the gauge hooked up and the ignition on, the gauge slowly rises to about 1/4 tank when the tank is almost full.



When I test the gage by putting a full 6 volts to it, the gage registers a full tank. When there is no voltage to it, it registers empty. The sender has a resistance of 155 ohms when the arm is in the down (empty) position and 75 ohms when it is at the full position. I assume the trick is to get the resistance of the sender to match the requirements of the gauge. Do I need to add some resistance to the circuit? If so, how would I do that? Or, perhaps, is the sender simply not the correct one for an original gauge?

 

Well Art, your kinda on the solution. I would insure you have a good ground. I assume your dealing with an original gauge. But you did not mention the vehicle. Assume again it’s a Ford. In 6 volt? Positive ground. There are some senders out their for that application. But most are designed in specific ohm value. That 75 full reading sounds high to me. Most I’ve delt with are much lower. My system 55 was converted to 12 volt neg ground. All SW steam gauges and a matched fuel system. It’s pretty accurate for now. I had issues with the ground. AJ

 

Stock sending units and gauges for your truck do not work on an ohms/resistance model that most cars and aftermarket components use. Instead, the stock units uses the The King-Seeley principle distometers where the sending units supply a full 6V through the heater wire in the gauge in the form of a square wave with the duration of the "on" being the variable determining the gauge reading. The longer the duration, the more fuel in the tank. It is this full 6v of current which heats the bi-metallic strip in the stock gauge that causes the gauge to read via a small gear train (that has some adjustability). As stated before, most after market sending units are simply a variable resistor which sends a constant voltage to the gauge, lessening that voltage as the fuel level goes down. Therefore, the sending units signal doesn't heat the bimetallic strip in the stock gauge in a meaningful way. Unfortunately, the calibration of the resistance/ohm after-market sending units and the stock gauges don't match up very well due to the differences in the principle of the signal.

Your choices essentially boil down to properly matching the style/parameters of your sender and gauge.

 

My vehicle is a 1953 F100 with a 239 8BA flathead V8 with positive ground. I was grounding it with a jumper directly to the battery. Yeah, I do think the sender resistance is too high. Thanks for your input.

 

Just a question, did you read the post from bmoran4?

 

Yes, and your point is?

 

Art the only thing I would see just to insure is to clean all the connections. And insure the instrument panel has a good solid ground. Your fuel has issues at least my tank did. Replaced it with a Taiwan top off. I installed anti chafe on the metal fuel tank straps. That killed the ground on the tank. And that’s where I found my grounding issue. It made no sense to me, because I had ran grounds from every rubber insulated mount on my 55. Including my rear pickup bed. Things started to work.lights were brighter and my turn signals were faster. My brake lites started working better to, I had changed that switch twice. And rebuilt my master cylinder. What finally fixed my fuel gauge. That had a matched unit meaning sender and gauge Stewart Warner, was a simple ground from my truck frame to another post on my tank. Kinda learned something and it still makes no sense. But the wire in ground went directly to my gauge. The other wire went from my frame to the tank. My old and new tank had a hole on each end. That’s where I installed that frame ground wire. AJ

 

Hey Art,

What sender are you using? If your not using a stock sender with the stock gauge then your probably not going to get an accurate gauge reading. Also if you don't already have one add a ground between the sender flange and a good frame or cab ground, after verifying your cab and frame is grounded, preferably to your main battery ground connection point on your engine.

 

Thanks, I will try that. I redid my tank about 2 years ago and have rubber (anti-chafe?) strips between the metal straps and the tank. I will run a temporary ground directly from the tank to the battery and see if that helps.

 

I bought a "43-4014 Gas Tank Sending Unit" for 53-55 F100s from LMC. My gage is stock original. Any idea where to find a matching sender? Thanks.

 

Looking at the LMC catalog, it looks like the sender unit you have is probably a re-production unit that probably is not compatible with your stock fuel gauge so it would probably just be easier to order the compatible re-pro fuel gauge with the sender you have which is LMC's stock number 47-1939.
And of course add a ground to the flange of the sender with a nice star washer.

 

The issue isn't resistance it is design. The repo sender units do not play with the original King Seely gauges - no matter what the seller claims.

Your best bet is to find a sender from someone moving their tank from the cab. I've picked up a couple this way (I've sold my extras, unfortunately). The same basic unit was also used on cars of the same era. You may need to adjust the arm a bit if that is the case.

It is my experience that you are well served by asking about the sender - even if the owner isn't trying to sell it. Often, they simply don't assign value to this part.

 

Thanks, that sounds like a workable alternative.

 

Great idea! I wish I had thought of that earlier. Thanks.