Sending unit on Boyd Tank

I just took the go-cart back out for a spin after some significant downtime doing various things. One of those things was a new Boyd Fuel tank. I bought the matching 0-90 ohm gauge from Autometer, reference P/N 1904 per recommendations/guidance I found on this forum. Tank is about a quarter full right now.

When I turn the car on the gauge needle just blips above empty. If I unhook the wires at the sending unit, the gauge goes immediately to full. This tells me the wiring is not grounding out to the sender but most likely somewhere in the sender itself. Additionally, I had the stock factory five fuel tank, sender and gauge before and it all worked fine.

If I keep the ground removed and just touch the green wire, the gauge immediately returns to 0. If I install the ground the same thing happens. If I swap the green and ground wire the same thing happens. If I ground directly to chassis instead of the wiring harness, same thing happens. No matter what I do, when connected, the sender does not appear to be working.

Suggestions? Bad sending unit came with my tank maybe? I have reached out to Boyd but just checking here in case there's a secret sauce I'm missing.

Bad sending unit it sounds like.

I had same thing happen several years ago. The sending unit on the Boyd tank was impossible to get anywhere near accurate even after they replaced it. They were good about replacing it, it just wasn't a very good unit I guess. Now I just grin and bear it because I don't want to pull the damn thing out again and replace it with a better quality unit. good luck.

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Originally Posted by Brave Salmon

I had same thing happen several years ago. The sending unit on the Boyd tank was impossible to get anywhere near accurate even after they replaced it. They were good about replacing it, it just wasn't a very good unit I guess. Now I just grin and bear it because I don't want to pull the damn thing out again and replace it with a better quality unit. good luck.

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Id be okay if it was even in the ball park. Its not working at all!

The "sending" unit is nothing but a "pot meter", the float rises and pushes the leaver which turns the pot-meter and that changes the resistance in the meter which results in a different gauge reading. It is important the the gauge and pot-meter go through the same range of resistance.

So when you have disconnected the wires the gauge reads full resistance (90Ohm) and goes to the full (assuming 90Ohm is for full reading). With the wires connected there is no resistance and the gauge reads empty so the gauge is most likely ok.

If you move the float (lever) up does the gauge change? if not, the pot meter is probably f.. er broken.

If you are still in "go kart " it should be pretty easy to remove the sending unit and bench test it to see if it is registering at all thru the full range of motion. Also very easy to hook up a vom and check for proper operation. I just received my new gauges (Classic Instruments),which comes with an identical appearing unit, and wanting to avoid the same scenario decided it would be a good idea to bench test the sending unit before installing in the tank and adding fuel. When I first checked it with the ohmeter I became alarmed because as I moved the float arm down towards the empty position the the meter wouldn't register past 200 ohms (range was supposed to be 33 - 240), so I used some test leads and actually hooked up to a 12v battery and the gauge as required and it appears to work fine with the gauge following the sender movement nicely thru the full range of travel.
Also,be aware that there is a great deal of adjustability to the sending unit and mine came with very specific instructions on initial set up for the correct dimensions to start with, but it should be possible to adjust it to give accurate readings for whatever the fuel level is, as long as the sending unit is actually working correctly.

I don't agree that your sending unit is not working at all, it is just not accurate. The testing you did shows proper functionality - full for anything over 90 ohms (you tried infinite, open circuit). When you start up, it does come off empty, just doesn't show 1/4 tank. I have the Boyd tank too and others have said, don't find it very accurate but it is what it is. The good news is that if you fill the tank up, it will read full.

Pull the tank and play with the sending unit if you want. Maybe there's an adjustment you can make

Steve

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Originally Posted by FF33rod

I don't agree that your sending unit is not working at all, it is just not accurate. The testing you did shows proper functionality - full for anything over 90 ohms (you tried infinite, open circuit). When you start up, it does come off empty, just doesn't show 1/4 tank. I have the Boyd tank too and others have said, don't find it very accurate but it is what it is. The good news is that if you fill the tank up, it will read full.

Pull the tank and play with the sending unit if you want. Maybe there's an adjustment you can make

Steve

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If i touch the green cable to ground it does the same thing. I have a little under half a tank of gas in the car. The needle is below empty mark but moves ever so little when power is applied to the guage.

Im pulling it tonight and taking resistance measurements in different positions. Either its broken, stuck or woefully misreading. If its the latter i might as well not have a sending unit.

If you're closer to half than 1/4 I'm inclined to agree. I think the gauge shows the tank less full than it is but shouldn't be that much out. I have noticed that it takes awhile to react as well - when I fill it up it is slow to show full.
WIll be interesting to see what you find.

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Originally Posted by FF33rod

If you're closer to half than 1/4 I'm inclined to agree. I think the gauge shows the tank less full than it is but shouldn't be that much out. I have noticed that it takes awhile to react as well - when I fill it up it is slow to show full.
WIll be interesting to see what you find.

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So I pulled out the sending unit and lo and behold the ohm reading changed from 0 to 95 by moving it. So I figured that the 3.5 gallons of gasoline I put in the tank wasn't enough. So I drove to the store, bought another 4 gallons and put that into the tank. No change. I read the ohm reading and it was 15.9 but the fuel meter was still reading just at the empty line. So I pulled the sensor again and connected the sender outside the tank to the connectors and move the level. Fuel gauge changed appropriately. I guess what must have been happening was the float was getting jammed up against the side of the tank. I adjusted it a little more towards the front of the tank. Hopefully that's all it was! It's now reading half a tank with 7.5 (ish) gallons in the tank. I guess that sounds about right? Thanks all.