15 Gal. Fuel Tank Sending Unit

AJM81CJ8

Door Breaker
City
Kalamazoo
State
MI
#1
Looking for recommendations for the sending unit for a 15 gal. tank. Going to replace mine soon and I'd like to fix the fuel gauge while I have the tank out.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#2
They're all basically the same, coming from the same factory. The one from MTS is the same as all the others. What it comes down to is spending a good chunk of time making sure it's calibrated correctly and adjusting the arm so that it meets your expectations. This isn't just a pull and swap sorta process. I've replaced my sender four times in the past 6 months. The last time was this week, and I spent a whole day making sure it was exactly how I wanted by adjusting the arm and reading ohms over and over and over again. Even used a scale I made to be sure it was reading right where I wanted at F, 3/4, 1/2, 1/4 and E.
F: ~12ohms
3/4: 16ohms
1/2: 23ohms
1/4: 40ohms
E: 72ohms
IMG_20200610_191906.jpg
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#4
Did you replace the plastic float with a brass one while you were at it?
I did not. I had a brass one, but it had a leak :/

I've gotten pretty dang good at dropping the tank and setting it back up. A couple hours start to finish now.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#7

AJM81CJ8

Door Breaker
City
Kalamazoo
State
MI
#8
They're all basically the same, coming from the same factory. The one from MTS is the same as all the others. What it comes down to is spending a good chunk of time making sure it's calibrated correctly and adjusting the arm so that it meets your expectations. This isn't just a pull and swap sorta process. I've replaced my sender four times in the past 6 months. The last time was this week, and I spent a whole day making sure it was exactly how I wanted by adjusting the arm and reading ohms over and over and over again. Even used a scale I made to be sure it was reading right where I wanted at F, 3/4, 1/2, 1/4 and E.
F: ~12ohms
3/4: 16ohms
1/2: 23ohms
1/4: 40ohms
E: 72ohms
View attachment 84354
Obviously, I need to make sure that my gauge is functioning, but from what I've read, if the coolant gauge is working, then the fuel gauge should be good. If you say that they are all the same then I will just get one coming. I'll have to make myself a set up board like what you have there. Any tips for making it? I assume that full is the bottom.of the filler neck inlet.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#10
Also, why do you have to keep replacing the sender?
Good question. In my limited experience, a quarter of them are bad out of the box. They're grounding out and when you put an ohmeter to them they just read 0 at all levels. On top of that, I've had a float get stuck so that it was reading a constant F. The other two times I've just been replacing the sender with an in-tank fuel pump (for an EFI LS swap), and then going back in there again to get the gauge to read better.

When you put your order in, order the float that @FLCJ8 listed - it should be worth the investment.

Full is maybe a little higher than the circular mounting face, at least it is on the 20g tank, but in any case the float doesn't go above that very easily and probably shouldn't.

What I would recommend is first getting a depth for your tank. I just put a measuring tape in there and measured from the bottom to the mounting surface for the sender. For the 20g tank that's about 11.25". For the 15g it's going to be more like 9"? Luckily, the 15g tank is more like a square box than the 20g, which has a slope at the bottom. Once you have a depth, you can divide it into quarters on a piece of posterboard or whatever. The sender has a couple of bendable tabs that you can use to change the range of the float swing arm. Start by getting F and E ohm readings, and adjusting the F (full) tab so that your ohm reading is about 12 when the float is all the way up. If your float is below the level of the mounting face, you can bend the arm so that it hits a line just at that level. Next, drop it down to E and bend your E tab so that you have a reading of about 72 ohms. Your float should be just above the bottom depth of the tank, too. Then go through 1/4 and 3/4 and see what they're reading. Most important I think is what it's reading at 3/4, because like I mentioned the most common problem seems to be a F reading until it's about half empty, then dropping very quickly to E.

I think that's a good start - if you have any questions don't be afraid to ask!
 

AJM81CJ8

Door Breaker
City
Kalamazoo
State
MI
#11
They're all basically the same, coming from the same factory. The one from MTS is the same as all the others. What it comes down to is spending a good chunk of time making sure it's calibrated correctly and adjusting the arm so that it meets your expectations. This isn't just a pull and swap sorta process. I've replaced my sender four times in the past 6 months. The last time was this week, and I spent a whole day making sure it was exactly how I wanted by adjusting the arm and reading ohms over and over and over again. Even used a scale I made to be sure it was reading right where I wanted at F, 3/4, 1/2, 1/4 and E.
F: ~12ohms
3/4: 16ohms
1/2: 23ohms
1/4: 40ohms
E: 72ohms
View attachment 84354
Do you happen to have the dimensions for the float? I was thinking about using a cork instead and was thinking about exploring that idea.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#13
Do you happen to have the dimensions for the float? I was thinking about using a cork instead and was thinking about exploring that idea.
I think that's a good idea, provided it's stable in gasoline. I can get an exact measurement when I get home.
 

AJM81CJ8

Door Breaker
City
Kalamazoo
State
MI
#16
I think I found my problem. Third picture is inside the tank. Upper right corner is what is left of the oem brass float. 20200620_104447.jpg 20200620_104531.jpg 20200620_104621.jpg
 
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