Fuel Sending Units and A-Body Fuel Tank Map

["Dart67"]

There are two Main Reasons that Aftermarket fuel sending units do not give accurate fuel level readings.

The first and most important is that the wire-wound variable resistance board on the stock sending units are shaped and wound for the tank that it was intended to be used in.
Therefore the resistance levels are not linear from end to end. Empty is somewhere around 73 ohm and Full is somewhere around 10 ohm with the in between readings changing in Non Linear steps.

Stock Non-Linear Board

The aftermarket sending units have wire-wound variable resistance boards that are a simple rectangle shape and wound so that they read somewhere around 73 ohm for Empty and somewhere around 10 ohms for Full with the in between steps going up in a linear manner.
The aftermarket sending units will never give a correct fuel level indication.

Aftermarket Linear Board

Non Linear Linear Fuel Sending Unit Difference

The other reason is that the float arm lengths are not correct for the tanks they are used in.

I have made a map of fuel levels in an A-Body fuel tank and a holding fixture which positions a sending unit at the correct height as if it were in a fuel tank.

Here are photos showing a stock sending unit and a aftermarket sending unit for comparison.

Stock Sending Unit

Aftermarket Sending Unit

You can see that the stock float is at the correct Full position while the aftermarket float reaches its Full position at about 5/8 of a tank.

Now you know why it seems to take forever for the fuel level to drop and then go quickly to empty.

I am and have been working on a calibration unit that is similar to the MeterMatch.

The calibration unit I am working on has a total of 11 set points. There are 9 set points from Empty to Full in 1/8 tank increments and 1 set point for a Low Fuel Alert(Steady On LED) and 1 set point for Low Fuel Alarm(Flashing LED)
Once all the set points are programmed, the reading are interpolated for a very smooth and accurate meter movement.

I am not yet ready to market or produce these units. They are in the testing mode and I need to figure out how to set up an LLC before I do much more.



Herb

 

[MoparMike1974]

Just so you are aware, there is already a similar product out there.
TechnoVersions - MeterMatch for Analog Gauge Correction

 

["Dart67"]

Just so you are aware, there is already a similar product out there.
TechnoVersions - MeterMatch for Analog Gauge Correction

Oh, I am well aware of this product. It is what prompted me to develop the unit I have. I posted about it back in April 2014 and bought one.

Solution to Fuel Gauge/Sender Problems

It is still not as accurate as what I wanted.
After talking with the gentleman that makes it about adding more set points to it and him having no interest. I designed and built my own unit which I feel is far more accurate.

Herb

 

[Dana67Dart]

Here are photos showing a stock sending unit and a aftermarket sending unit for comparison.

That is awesome.

I bought an OE "but newer replacement part number" and it functions way better than the aftermarket POS that was in the tank.

I wish I had a 67 OE unit working or not. I understand why the aftermarket makes them the way they do but would it be so hard for them to make the float have the correct travel at least!

Keep up the work and don't let the naysayers stop you from making an awesome product!

 

[MoparMike1974]

On my car it goes from full to empty in about 50 miles. Then I have no idea how much gas is in the tank. I bought the meter match but have not got around to installing it yet. For now im documenting my mileage at every fill up just to keep track of my fuel.

 

[Dana67Dart]

For now im documenting my mileage at every fill up

My dad did that for a decade in his dart.

 

[kursplat]

My dad did that for a decade in his dart.

ha, i used to keep track in my head. "uh, let's see. 3 days to work and back, 6 burnouts, drivin' around with the gf...." sometimes the math didn't work out so well

 

[Dana67Dart]

sometimes the math didn't work out so well

especially with the GF in the car... darn ran out of gas. guess we will have to park for a while.

 

[Jasonmiester]

Been doing some testing, trying out different makers, whom all seem to suck. Way off, tried to calibrate, but it’s only correct in one particular spot in the gauge...
what a pita.... why can’t they just make it right?

 

[KitCarlson]

I played with this years ago, but my gauge still works. I will share design, and help with programming. Gas gauge calibration unit

 

[Wagon of Death]

Interested...my gauge doesnt work at all and neither does the odometer...Permanent jerry in the boot and getting by on guess work...Ive run out 3 times in a year

 

[67Dart273]

Something that might be missing in this thread is that along with the sender, the 50 year old gauge itself might be AFU

 

["Dart67"]

Something that might be missing in this thread is that along with the sender, the 50 year old gauge itself might be AFU

Del,

I agree with you that the dash gauge can also be a problem.

As most all of the "My gas gauge does not work" post have to do with the tank sender unit, I thought I would try to show and explain the 2 main reasons for the problem.

As you and many others know, there are far more reasons for the fuel gauge to not work.

Herb

 

[SpaceDemon]

Del,

I agree with you that the dash gauge can also be a problem.

As most all of the "My gas gauge does not work" post have to do with the tank sender unit, I thought I would try to show and explain the 2 main reasons for the problem.

As you and many others know, there are far more reasons for the fuel gauge to not work.

Herb

Honestly with all the problems on calibration I've been looking through, and the only gauge I have working right now is the amp meter, part of me just wants to make a Mad max S.O.L. light

 

[famous bob]

Honestly with all the problems on calibration I've been looking through, and the only gauge I have working right now is the amp meter, part of me just wants to make a Mad max S.O.L. light

View attachment 1715252223

IN MY CASE, MY CAR IS TOTALLY REWIRED, NO STOCK GAUGE, NEW SENDING UNIT THAT IS THE SAME LENGTH AS THE STOCK ONE BUT W/ 3/8 PICKUP TUBE , USED AS A RETUN W/ THE SOCK CUT OFF, NEW WIRING, GROUNDED, W/ A DIGITAL AFTERMARKET AMP REDUCTION THINGY, AND IT STILL DON`T WORK RIGHT. -------------------Not screaming ,poor finger pecker ! LOL
Not pulling the tank till maybe a mini tub, but that`s another story.

 

[4spdragtop]

Nice work Herb! The visual you provided helps me understand how it works.
Thanks for posting.

 

["Dart67"]

Mad max S.O.L. light

I have not followed the Mad Max movies. What is a Mad max S.O.L. light ?

 

["Dart67"]

Nice work Herb! The visual you provided helps me understand how it works.
Thanks for posting.

You are Welcome...

 

[MileHighDart]

I get what your doing with the calibration unit, etc. But aren't you / we still going to have to extend the arm that the float is on to the correct length too?

 

["Dart67"]

I get what your doing with the calibration unit, etc. But aren't you / we still going to have to extend the arm that the float is on to the correct length too?

Yes, the arm would have to be lengthened if you wanted the correct levels past its stop point.

 

[SpaceDemon]

I have not followed the Mad Max movies. What is a Mad max S.O.L. light ?

In the movie as he's being chased a red light comes on to let him know that he's almost out of gas (I take it the original gauges didnt work anymore). It looks to be a tow trailer brake light Jerry rigged up to the steering column.

 

[DLJ]

Trying to figure out what to do to make my fuel gauge work, at least showing Full when full and Empty when it's got a gallon or 2 in it.

Would appreciate if any experts could help me with a few questions and perhaps suggestions.

My Dart has the original OEM Fuel Gauge at dash and I still have the OEM sending unit that had a fatal corrosion problem at the middle of the steel tube due to our ridiculously bad gas around here. Now I am reviving the Dart and had to replace it with a new aftermarket sending unit that never gave a correct reading, most of the time it reads empty as if there is a bad connection or unplugged something.

I had to replace the gas tank due to corrosion too, using a plastic tank available here, which requires sending unit tube bending adjustments to reach bottom (it was 2" far from bottom) and also float adjustments.

Can I make readings playing with the send unit outside the tank? Did that for a while and melted the plastic plate that holds the resistance wire in the sending unit...

What I am curious about is if there is anything between the sender unit and the reader at the dash, it seems to be something (from factory) added to the instrument cluster and connected to the temp and gas gauges at the dash, as shown on pics, any idea what that is and what it does?
Thanks for any input.

View attachment 1715320010

View attachment 1715320011

View attachment 1715320016

 

[Mike69cuda]

I have an aftermarket sender and I have got it working pretty good with a Meter Match. I think it might be +/- about a gallon accurate. I have been refilling the gas a various readings on the gauge to check accuracy.

Being the lazy guy that I am, I just used the charts I found here on the forum and programmed the meter match with resistors. It was very easy, no crawling under the car and getting a face full of gas like I usually do when I mess with a fuel tank. I had my dash out, so I did it all on the bench.

I also replaced the ivr, which I understand you have to do to use a Meter Match. I made my own ivr, being a cheapskate. Mine is a rally dash, so the ivr was in the fuel gauge, so I had to have the dash out to do it.

I will post my procedure and the resistor values sometime soon, but can talk you through it if you want to do it before I get to it.

 

[DLJ]

I have an aftermarket sender and I have got it working pretty good with a Meter Match. I think it might be +/- about a gallon accurate. I have been refilling the gas a various readings on the gauge to check accuracy.

Being the lazy guy that I am, I just used the charts I found here on the forum and programmed the meter match with resistors. It was very easy, no crawling under the car and getting a face full of gas like I usually do when I mess with a fuel tank. I had my dash out, so I did it all on the bench.

I also replaced the ivr, which I understand you have to do to use a Meter Match. I made my own ivr, being a cheapskate. Mine is a rally dash, so the ivr was in the fuel gauge, so I had to have the dash out to do it.

I will post my procedure and the resistor values sometime soon, but can talk you through it if you want to do it before I get to it.

View attachment 1715319961

Hi and thanks for your response.
You seem to be very skilled with electric devices, which I am not much so it might be simple for you but I really don't want to go that far to make the fuel indicator work, there must be a simple way at least to read accurately the full tank and the low fuel...
I have a few old family cars from 70's that my dad bought new and all of them have the slant fuel tank bottom and none of the readers ever told the correct % of fuel left in the tank, the 1st half takes longer to spend and when the meter showed half tank, it actually had 1/4 but we got used to that... what cannot happen is having a wrong reading when the fuel is low... risking run out of gas...
I paid good money for the cheap aftermarket sending unit which should be made as stock but have no idea how to test it.
Once I must have the original sending unit I guess I'll try to compare both and perhaps use the resistor from the old rusted out unit in the new one, if it works...

 

[Mike69cuda]

I think I may be able to distill it down to a procedure that would be easy to follow. Let me see what I can put together. Read the Meter Match site & see if it makes sense.