Fuel Sender calibration using Meter Match

[HWYCRZR]

I decided to start a new thread going through my fuel sender calibration instead of cluttering up the fuel sender rebuild thread. Fuel Sender Rebuild

It started with my repro sender would never get quite to full. 3/4 was about max. When I was browsing I stumbled onto the thread above and decided to rebuild my original sender. During the rebuild I bench tested it and hooked it up to my instrument panel. It was looking good.

 

[HWYCRZR]

Next step was to install it and fuel up.
Once I got it in the tank and hooked up, the low end towards empty was looking good. Once I filled it up I barely got over 1/2 a tank. Checking the resistance of the sender in the tank with full fuel I was sitting at about 26 Ohms from the sender. WTF.
I did order a phone scope that should be here around the first as I really am interested in where the float is positioned with full fuel. Is it stuck half way? Or does the new tank not have the depth as the old not allowing full tank float height. I still am going to investigate, but in the meantime. @Big_John suggested I try a Meter Match, which allows you to calibrate the high and low end of your gauge.
Gas Gauge Fix

Meter Match installed and full tank set. I did not yet set the low end as I figured it would be close. But I was mistaken.

 

[Joseph James]

I have the same problem and considered dropping the tank and using a clothes hanger to manipulate the float and observing what I need to do.

Good luck.

I have considered calling Murray to see if he has any old ones. Probably better than the Chinese junk I have now. Mine is 1/2 when full.

 

[HWYCRZR]

(Copied from the other post so I had my data in one thread)I first calibrated the meter match with an almost full tank. I set it to full. Then I decided to top it off it took less than a 1/2 gallon. When I turned the ignition back on it showed way over full. (Did my sending unit all of a sudden break loose and start working?) I should probably crawl under tomorrow and ge an Ohm reading. I re- calibrated the Meter Match back to full. Real easy to set. After about 200 miles I will have to check where the gauge is sitting. I want to run it out to set the low end. I probably won’t set any mid points.

View attachment 371224 View attachment 371225

 

[Big_John]

One thing I did, and have done in the past, was to run a separate ground wire to the sender housing. Yea... That fuel line clip is supposed to do the job, but I figure that paint, rust and dirt is going to insulate the fuel line from making a good ground. It's all about making the conditions as good as possible so you don't have any added resistance.

I soldered a blade connector to the housing.

 

[HWYCRZR]

Today I took it for a drive and every little slope, braking action and acceleration would cause the gauge to fluctuate between full and half. It seemed my Meter Match was way too sensitive. I thought that maybe it was a little goofy because I hadn’t set the low end.

 

[HWYCRZR]

One thing I did, and have done in the past, was to run a separate ground wire to the sender housing. Yea... That fuel line clip is supposed to do the job, but I figure that paint, rust and dirt is going to insulate the fuel line from making a good ground. It's all about making the conditions as good as possible so you don't have any added resistance.

I soldered a blade connector to the housing.

View attachment 371451

The issue is I get the same resistance reading whether both terminals of the Ohmmeter are hooked directly to the sender or if I hook one end to the sender and one end to the frame. Or if I check it by the instrument panel. I am still getting around 26 Ohms on the sender. Which should be around 10.

 

[Big_John]

So, 26 ohms no matter what.. Correct?

 

[HWYCRZR]

When I got home I decided to hook my test tool up to the sender wire and set the resistance at 64 ohms, which was my measured empty. My gauge went to pegged past full. Wow the low end of the Meter Match was way off. It probably explains some of my wild swings. I opened the Meter Match and set it to Number 4 to adjust the low end. The down button wouldn’t move it. But the up button would bring it down to half. Not meaning to, I turned off my ignition while it was still in the set mode. It seemed like it reset when I powered it back up. The down button was working like it should. I brought it down to empty and hit set and turn the dial back to run. I then went back under and ran my tester down to 26 Ohms ( where my sender read at full tank). And sure enough the gauge read full. I hooked the sender back up and the gauge went to about 7/8 of a tank which is probably about right after my drive this morning. I will go for another drive tonight or tomorrow and check if the fluctuation is better.
Pictures of the instructions.

 

[HWYCRZR]

So, 26 ohms no matter what.. Correct?

Yes. That is why I want to see the float position so bad. Why isn’t going all the way to the upper position which is 10 Ohms (measured on this sender with it all the way to the top). Is my reproduction tank from Vans thinner than my original not allowing full range? I don’t know if I have ever gotten up to 18 gallons in this tank at the pump . Specs say 24 gallons. I would like a thickness measurement of an original ‘68 tank. The fuel tank straps have another 2-2-1/2” of room for a thicker tank.

 

[HWYCRZR]

There are a couple of other settings I can check if I still get fluctuations. There is a “reading averaging” mode. That can smooth things out. This thing is pretty cool there are a lot of things it can do.

 

[Ross Wooldridge]

Watching with interest.

 

[HWYCRZR]

I just went for a spin. I am getting fluctuation still, but quite a bit less. I think I figured out why that when I hit the brakes or slow down to a stop the gauge goes up and when I speed up it am driving steadily the gauge is down from when I am standing still. Also when the ignition is on it reads higher than when it is running. It is my voltage that is causing the movement. When the voltage goes down my gauge goes up. When my voltage goes up my gauge goes down. This is due to the power in the Meter Match fluctuating causing the resistance to change. Again another setting on the Meter Match.
“Voltage Correction”. It says that the reading may change significantly between 12.5 volts (battery) and 13.8 (voltage regulator).
I am getting closer.

 

[HWYCRZR]

I turned the voltage correction on. Now I at least get the same reading running as I do with just the key on. After 40 miles I am just over 3/4 tank reading. At around 12 mpg I have probably burned a little over 3 gallons. With 20? Usable gallons, that is probably about right. Will drive again tomorrow and see if I get the stopping fluctuations. I want to drain the gas down and go until I run out and check out the empty end. I want the needle to be below empty when it runs out.

 

[cbarge]

 

[cbarge]

I am going to order one for the Boab
Even with the RTE electronic volt limiter it never did read accurately. Full was 3/4. 1/4 is half but empty is empty,lol

 

[HWYCRZR]

I took it today to get burgers. Way less fluctuation since I turned on the voltage fluctuation. It moves pretty fast between 3/4 and 1/2. I suppose there is more vertical travel on the float arm when it gets closer to horizontal, then would slow Down again as the arm is down further on the radius. My biggest mistake is I should have started with my repro I ran last year. Wouldn’t go past 3/4, but did not fluctuate. I rebuilt my old one threw it in and started tweaking it. So now I don’t know if I am fighting the meter match or the rebuilt gauge.

 

[HWYCRZR]

Interesting phenomenon. Key on or running same level. As I start driving it goes down about 1/4 and doesn’t come back until I stop. Even at steady highway speeds. Next step before I put my repro sender back in, I will bypass the Meter Match and see how much movement my gauge has with out it. I should also hook up my ohmmeter to it while I am driving to see what is happening. Need to set up my GoPro on then Ohmmeter.
Here is some video of my gauge when driving
First video is from a stop up to highway speed 55 mph. Second is Hwy speed to slowing down and turning. Last picture is sitting still running after the video on level ground.

 

[HWYCRZR]

I re did a bunch of ohmmeter readings. I have come to the conclusion that my original sending unit is a little too active. A slight jounce of the car sends my ohms up or down about 10. The good news is I get the same reading up by my dash as I do down on the sender. So at least my wiring isn’t causing issues. I got my scope camera, but need to remove my fuel neck to see anything. It drops down too much so forces it to the bottom. Also it doesn’t seem to focus very far away from the lens in gas.
Time to put this one back in. I know it doesn’t fluctuate. It just won’t get past 3/4. I should be able to fix it now.

 

[HWYCRZR]

Not impressed with this Ryobi scope. Not very bright and the focus and definition isn’t that good. Maybe it will be better in a smaller area or somewhere with a little more light.