Fuel tank sending unit calibration thread

[hemi68charger]

Hey gang..
OK, I tried.... I searched... There was a great thread here once in which someone did a topic on how to properly adjust position one's fuel sending unit swing arm for accurate readings. I'm about to put a new tank/sending unit in the Daytona. Also, isn't there a thread on how to bench test a sending unit by placing it into the circuit of the gauge and power supply? Where would I position the sending unit? I would place it between the gauge and the negative post of the power supply? Also, the flat portion of the gauge needs to be grounded as well to the negative post of the power supply?

Thanks..

[Dans 68]

Try this and the linked threads. http://www.dodgecharger.com/forum/index.php/topic,68459.msg768767.html#msg768767  If you cannot find a thread that shows the sending unit in a testing circuit I will draw it up for you (has to be later, though  ).

Dan

[hemi68charger]

Dan, does this make sense?

I understand the resistance theory behind the sending unit, but I also want to tie it into my 5v circuit here and watch the reactions of the fuel gauge. I know I need to isolate both the sending unit and gauge and test independently. My test here also is to additionally calibrate the actual gauge. I can test the qauge by isolating it in my setup I have and change the various resistance valves and observe the reactions of the aguge. Again, I wish to test the complete gauge/sending unit system as one. To do that, I need to combine the sending unit into the gauge's circuit. I'm guessing since the sending unit body needs to be grounded, I need to run a lead from the body to the negative post of the power supply. The sending unit post would attach to the sending unit side of the gauge. The other side of the gauge will be the 5v power supply....  Make sense?

I will also test the gauge by itself with the specific resistance values (full and empty ohms) with my resistor box.

[Back N Black]

What i did was lay the sending unit on the floor and ran a jumper wire to the fuel sender blue wire and grounded the sending unit. use your multimeter and check the resistance as you move the float arm to empty,half and full. The gage in the dash will move also, that way you can adjust accordingly.

[Dans 68]

Dan, does this make sense?

I understand the resistance theory behind the sending unit, but I also want to tie it into my 5v circuit here and watch the reactions of the fuel gauge. I know I need to isolate both the sending unit and gauge and test independently. My test here also is to additionally calibrate the actual gauge. I can test the qauge by isolating it in my setup I have and change the various resistance valves and observe the reactions of the aguge. Again, I wish to test the complete gauge/sending unit system as one. To do that, I need to combine the sending unit into the gauge's circuit. I'm guessing since the sending unit body needs to be grounded, I need to run a lead from the body to the negative post of the power supply. The sending unit post would attach to the sending unit side of the gauge. The other side of the gauge will be the 5v power supply....  Make sense?

I will also test the gauge by itself with the specific resistance values (full and empty ohms) with my resistor box.

Yep, it makes sense. I've attached a sketch I did a while ago, and you only need to replace the resistor with the fuel sending unit to complete the circuit; the orientation does not matter (it is just a resistance in the circuit). The only detail that you cannot control, unless you use the gas tank, is to know exactly how much float arm movement, and thus resistance end points, you are getting in the tank. The only way to really know is to install the sending unit in the car, fill the tank full and measure the resistance from the sending unit. Then empty the tank and repeat. This will give you your endpoints. Then do bench testing to put the full and empty settings where you want them on the fuel gauge. Simple, but a bit time consuming to do. And this is really only necessary if you are a bit retentive (like I am). Good wrenching!

Dan

[hemi68charger]

Bingo... I knew I'd find it soon.. I'll bookmark this one when I get home... Thanks oldcarnut for the detailed thread........

Thread with tank/sending unit cross-section cutout

[Dans 68]

Bingo likewise.    I missed this thread completely.       Good photos. It is now bookmarked.

Dan

[hemi68charger]

You'll see the gauge reacted to the 10 ohms from the resistor box appropriately, full. The fuel sending unit after some tweeking registers 9.5 ohms for full. So, things seem to line up.

Here's my setup and a little video I took today. I swapped out the tank today.

http://www.youtube.com/watch?v=JHzrdg8AcAw

[oldcarnut]

Nice vid.  Sure seems easier to be able to look through the side of the tank then the other end.

[hemi68charger]

Nice vid.  Sure seems easier to be able to look through the side of the tank then the other end.

One advance of a Charger...... 

[hemi68charger]

Man, the design on these sending units stink...... Half a tank of fuel and I'm only reading about 44 ohms, at a level position,  which equates to between an 1/8 and 1/4 tank of fuel when it should be 1/2. I have about 10 gals. in a 19 gal tank. The took the ohms reading at the tank, it measured 44 ohms. I put 44 ohms to the gauge on my work bench and they both read the same, low for reality. I did notice that the position of the float halfway through the travel arc placed the arm nowhere near 22 ohms, which equates to 1/2 a tank... Grrrrrrrrrrrrrrrrr

[maxwellwedge]

  AB - THEY ARE ALL JUNK!

[hemi68charger]

 AB - THEY ARE ALL JUNK!

At least then I don't have to beat my head against the wall...............  Thanks for the encouragement and validation.......... Guess it's time to find an NOS one.. Yeah, right.................

OK Jimbo............... Where do you send yours off to get fixed, get "good" ones or send originals off to get fixed?  Or, the biggest "or", you just live with it?