Fuel sending unit results..what to do?

[Trump_XLV]

Hello everyone,
I made a post a while ago inquiring about the sending units and the correct readings for one so when I inspect mine I’ll know what I’m reading.

Today was the day I could test mine
I know that the proper readings are as follows
“For measuring the resistance values of the sending unit at "empty", "half", and "full", use the following numbers:

Chrysler Specification:
Empty = 72 Ω
Half = 22 Ω
Full = 9 Ω

Miller Special Tool Specification (used by Chrysler for testing):
Empty = 75 Ω +/-5% -> 71.2 - 75.8 Ω
Half = 22 Ω +/-5% -> 20.9 - 23.1 Ω
Full = 10 Ω +/-5% -> 9.5 - 10.5 Ω”

My readings were
Empty= 66-68
Half = I couldn’t get the the best reading here and will try again but from empty to full it did gradually go up so I suspect it to be fine.
Full = 11-12. I did get it to read 9 one time but couldn’t get it back again.


Could someone give me an idea of what this would look like on the fuel gauge if I leave it this way? Is there a chance I run out of gas because it’s reading 1/4 and it’s really on empty? Or are my readings close enough to not see that big of a difference?

My unit seems to be original and would hate to replace with another + buy a meter tech. I could just buy a meter tech I suppose but if this 90% accurate I feel like it’s close enough. Not sure how much 66 ohms off of 75ohm will make a difference.


Thanks for your time

 

[67Dart273]

I've posted this before. Some folks are selling rheostats on egag for not much that would be handy. You can set them for the resistance you want and then evaluate the gauges reading

I actually have an aftermarket gauge tester that uses a pot instead of switched resistors. It has info in there for testing Fords, Mopars, and others. Don't remember who made it. I've had a house fire, and things are in a shambles, plus some things, I just dont have anymore.

There are, or were, several sellers (or maybe, one seller with multiple screen names) so if you can't find this one, use the title wording to search for others

Pardon Our Interruption...

If you are not into electronics, the basic difference between a "pot" (potentiometer) and rheostat, is that a pot has 3 terminals to be used as a voltage divider, and a rheostat is normally considered to have only 2 terminals. You only need 2, so you could use either, or "being called" by either

 

[RedFish]

73 is empty, 23 is half, half of that span is 25. 73 minus 25 equals 48. Guess what 48 is not 1/4 tank. 1/4 tank is closer to 34. Running out while the gauge shows 1/4 ? Stranger things have happened but I would bet against it. To see empty while you still have a 1/4 or more is much more likely. Your test results show close enough.

 

[Kern Dog]

73 is empty, 23 is half, half of that span is 25. 73 minus 25 equals 48. Guess what 48 is not 1/4 tank. 1/4 tank is closer to 34. Running out while the gauge shows 1/4 ? Stranger things have happened but I would bet against it. To see empty while you still have a 1/4 or more is much more likely. Your test results show close enough.

 

[Kendog 170]

I purposely ran my Ragtop out of gas with my aftermarket sender so I would know exactly where on the gauge it runs out. Turns out exactly on the empty line. No higher, no lower. That was my only concern.

 

[RedFish]

I purposely ran my Ragtop out of gas with my aftermarket sender so I would know exactly where on the gauge it runs out. Turns out exactly on the empty line. No higher, no lower. That was my only concern.

Year model makes a difference. Your fuel gauge may be a different animal. At this point I'm not sure which is which. Exactly on the empty hash mark varries with viewing angle too.

 

[340six]

I purposely ran my Ragtop out of gas with my aftermarket sender so I would know exactly where on the gauge it runs out. Turns out exactly on the empty line. No higher, no lower. That was my only concern.

What brand was it.

 

[Kendog 170]

I don't recall. I think E-bay.

Exactly on the empty hash mark varries with viewing angle too.

Well from my angle I know I'm screwed if I don't fill up. lol

 

[Trump_XLV]

73 is empty, 23 is half, half of that span is 25. 73 minus 25 equals 48. Guess what 48 is not 1/4 tank. 1/4 tank is closer to 34. Running out while the gauge shows 1/4 ? Stranger things have happened but I would bet against it. To see empty while you still have a 1/4 or more is much more likely. Your test results show close enough.

Thanks. It’s what I thought as well.

 

[67Dart273]

If you can't get it accurate, there is always the "meter match" device, and now there are copycats, imported of course, on egag

 

[Vaanth]

Hello everyone,
I made a post a while ago inquiring about the sending units and the correct readings for one so when I inspect mine I’ll know what I’m reading.

Today was the day I could test mine
I know that the proper readings are as follows
“For measuring the resistance values of the sending unit at "empty", "half", and "full", use the following numbers:

Chrysler Specification:
Empty = 72 Ω
Half = 22 Ω
Full = 9 Ω

Miller Special Tool Specification (used by Chrysler for testing):
Empty = 75 Ω +/-5% -> 71.2 - 75.8 Ω
Half = 22 Ω +/-5% -> 20.9 - 23.1 Ω
Full = 10 Ω +/-5% -> 9.5 - 10.5 Ω”

My readings were
Empty= 66-68
Half = I couldn’t get the the best reading here and will try again but from empty to full it did gradually go up so I suspect it to be fine.
Full = 11-12. I did get it to read 9 one time but couldn’t get it back again.


Could someone give me an idea of what this would look like on the fuel gauge if I leave it this way? Is there a chance I run out of gas because it’s reading 1/4 and it’s really on empty? Or are my readings close enough to not see that big of a difference?

My unit seems to be original and would hate to replace with another + buy a meter tech. I could just buy a meter tech I suppose but if this 90% accurate I feel like it’s close enough. Not sure how much 66 ohms off of 75ohm will make a difference.


Thanks for your time

For your measurement readings, as compared to specifications, the needle would read as follows:

- Empty= 66-68 ohms --> Gauge will likely read a little higher a the "E" mark, perhaps about the needle's thickness or so, depending on the gauge's own calibration.

- Half = from empty to full it did gradually go up --> in general, the hallway point is not of great concern with the gauge end points reading reasonably good. This point is typically of more concern in gauge calibration than sender reading.

- Full = 11-12 ohms ... 9 one time --> Gauge might read a little low at the "F" mark. However, neglecting lead and test point contact resistance, the reading is likely closer to specification. Likely a not noticeable difference in needle deflection.

For the empty position, bending the stop tab slightly to allow further movement of the float arm will allow for a resistance reading closer to specification, but minimize any bending to prevent arm mechanical over travel.

Note that gauges can be calibrated separately or to the sender and circuit, which can offset or add to sender differences. Gauge calibration is not dictated in this case for the sender values seen.

For the readings that you have, considering the difficulty in attaining exact numbers without using fixtures, and considering this is an original Chrysler sending unit in good shape, install it and go.

---

Additional Note About Measuring Low Resistance Values

When measuring low resistances, such as ballast resistors or the lower end of the fuel sending unit winding, account for the resistance of the test leads connected to the measuring device. This can be done by shorting the leads together, noting the resistance, and subtracting it from the measurement readings, or use the meter's relative setting (if equipped) similarly with the lead shorting, or use a meter that measures conductance and convert accordingly, or use a four wire ohms measurement setup with the appropriate device.

Note if the test leads' resistance is higher than about 1/2 ohm, better leads should be used, to reduce error and provide simpler accounting for test leads added resistance.

 

[67Dart273]

^^Most meters are not very accurate below an ohm, so trying to argue about 1/2 ohm is a waste of tme^^

The fact is the OEM senders and the gauges ARE NOT LINEAR. This simply makes it difficult to attempt to scale readings and predict the outcome

 

[Michael Siple]

My gauge always leaves me with a cushion - maybe 3-4 gallon & I like that.

 

[gary h]

Does anyone rebuild the Senders anymore ?