Fuel gauge/sender converter

[J-440]

 I have an electric fuel gauge from Stewart Warner and a gas tank/sending unit from Rick's.  The 2 are not matched with the same ohms so my gauge is not working.  Instead of dropping the tank and sending the unit back to Rick's, is there a device that I can splice into the wiring to get the 2 on the same ohm reading?  I'm calling Rick's on Monday but wanted to see if I can fix it today.  Any electrical gurus out there?

[John_Kunkel]

The S-W sender has a range of 33-240 ohms which is a ratio of over 7-1, the Mopar sender has a range of 10-73 ohms so the ratio is roughly the same and the S-W resistance is roughly 3 times higher. I would guess that you could put a resistor in the wire leading from the gauge to the tank but it'll take somebody smarter than me to compute the value of the resistor.

[J-440]

 Found a device called a fuel gauge interface module from Speedway Motors.  Runs about $130 and splices in between your gauge and sender and is compatible with all gauges and senders.  Since my current gauge is not adjustable and I dam sure as hell don't wanna drop the tank and send back to Rick's, this is a better option.

[lukedukem]

So will this work is you have the stock gauge and after market sending unit. When I fill my car up it only goes to 1/4 tank.

Luke

[Dino]

So will this work is you have the stock gauge and after market sending unit. When I fill my car up it only goes to 1/4 tank.

Luke

Only if the resistance ratio is the same will it be a matter of adding a resistance, it gets a bit more complicated if it's not.

J-440 why do you need to drop the tank by the way?  I replaced my sending unit without doing so without any problems.  If you want to keep the gauge then just buy a matching sending unit and return what you have.  Or send it back to have the resistance changed.

[lukedukem]

is there a sending unit that works correct with the factory gauge then....

luke

[Dino]

There is not, only the stock sending unit is matched to the stock gauge.  To remedy that I followed Charger-Bodie's lead and transplanted the resistance box from the stock sending unit onto the bigger repro unit.  The gauge now reads as it should, but you can never get it right with an unaltered repro sending unit.

[John_Kunkel]

Here's a link to the device J-440 found:

http://www.speedwaymotors.com/Fuel-Gauge-Interface-Module,66534.html

Reading the instructions PDF it looks like it covers the entire range of popular senders.

[lukedukem]

Here's a link to the device J-440 found:

http://www.speedwaymotors.com/Fuel-Gauge-Interface-Module,66534.html

Reading the instructions PDF it looks like it covers the entire range of popular senders.

john, in your opinion, would this device work in my situation? i have stock fuel gauge but aftermarket sending unit in the tank.

luke

[hemigeno]

I'm messing with my fuel sending unit right now too, and it's a stock unit.  While I'm no expert when it comes to electronics, I'm not sure it would be possible to retrofit any aftermarket sending unit to read correctly with the stock Chrysler gauge.  The limits for the gauge itself are as follows:

At E / Empty:
73 ohms +/- 12 ohms

At F / Full:
9.6 ohms +/- 1 ohm

I have an old test box on which you can dial up a specified amount of resistance (00.1 - 99.9 ohms), and I checked my gauge's accuracy plus the integrity of the wiring harness by hooking this box up in place of the sending unit back by the tank.  My gauge reads spot-on at the aforementioned resistance settings.  10.6 ohms put the needle right on the vertical white tick/mark of "Full", and 61 ohms was ever so slightly above the "Empty" vertical white tick/mark on the gauge.

From my non-professional perspective, I don't know if it would ever be possible to reduce the resistance of an aftermarket sending unit below its lowest reading (MAYBE if you messed with the actual coiled wire which creates the resistance).  Adding reistance, yes... but reducing?  If the lowest it goes is 33 ohms, that's probably going to read less than 3/4 of a tank.  Just about what my old R/T used to show if I squeezed every drop into the tank at fill-up time.  Without finding some way to add a small amount of current back into the fuel gauge circuit to trick the gauge into 'seeing' a lower resistance, you'd be heading in the wrong direction.  That's why these mis-matched setups never - ever - read "full".

Once ECS gets done perfecting OE-style trunk mats, maybe Chrysler fuel sending units should be added to their product line.  

[lukedukem]

Thanks for the info hemigeno, when I fill mine up it goes to almost halfway. I'm also thinking about taking mine out and checking it out to see if I can make it better.

Luke

[Pete in NH]

Hi,

Here's another gauge converter unit. I don't anything about it but, it looks like it's less expensive than some others out there.

http://www.technoversions.com/MeterMatchHome.html   

[lukedukem]

Hi,

Here's another gauge converter unit. I don't anything about it but, it looks like it's less expensive than some others out there.

http://www.technoversions.com/MeterMatchHome.html    

reading on that it says it will work for mopar cars for the 60s. I'm gonna buy one and see if it works.


Luke

[tan top]

I'm messing with my fuel sending unit right now too, and it's a stock unit.  While I'm no expert when it comes to electronics, I'm not sure it would be possible to retrofit any aftermarket sending unit to read correctly with the stock Chrysler gauge.  The limits for the gauge itself are as follows:

At E / Empty:
73 ohms +/- 12 ohms

At F / Full:
9.6 ohms +/- 1 ohm

I have an old test box on which you can dial up a specified amount of resistance (00.1 - 99.9 ohms), and I checked my gauge's accuracy plus the integrity of the wiring harness by hooking this box up in place of the sending unit back by the tank.  My gauge reads spot-on at the aforementioned resistance settings.  10.6 ohms put the needle right on the vertical white tick/mark of "Full", and 61 ohms was ever so slightly above the "Empty" vertical white tick/mark on the gauge.

From my non-professional perspective, I don't know if it would ever be possible to reduce the resistance of an aftermarket sending unit below its lowest reading (MAYBE if you messed with the actual coiled wire which creates the resistance).  Adding reistance, yes... but reducing?  If the lowest it goes is 33 ohms, that's probably going to read less than 3/4 of a tank.  Just about what my old R/T used to show if I squeezed every drop into the tank at fill-up time.  Without finding some way to add a small amount of current back into the fuel gauge circuit to trick the gauge into 'seeing' a lower resistance, you'd be heading in the wrong direction.  That's why these mis-matched setups never - ever - read "full".

Once ECS gets done perfecting OE-style trunk mats, maybe Chrysler fuel sending units should be added to their product line.  

yeah think ECS is the Man for the job too ,  to  reproduce a , accurate Chrysler  fuel tank sender unit , to work with stock OEM gauges 

[lukedukem]

I'm tempted to take mine out and mess with it but the weather turning out good down here and I just put new brakes on and I'm wanting to drive it bad. Maybe if I have a rainy weekend. Which in south Texas that could be any time

Luke

[remta1]

hmm i have a similar problem on 69 Plymouth satellite should I be looking for a new guage that reads 10  to 73 ohms
was looking at an aftermarket guage that reads 0 to 90 ohms ..is this wrong ?

[Pete in NH]

Hi,

The gauge and the sender have to match resistance wise. If you have a stock Plymouth gauge you need a stock 10 to 73 ohm sender in the tank. If you have an aftermarket gauge you need a matching sender or one of these little converters talked about above in this thread.

One big problem with most reproduction Mopar fuel sending units is they may reproduce the 10 to 73 ohm range but the original Chrysler parts had a non linear resistance curve to them and most repro parts are linear curves. This causes the gauges to read wrong anywhere between full and empty. Not a great feature when you want to know how much gas you have in the tank.

[red79]

From my non-professional perspective, I don't know if it would ever be possible to reduce the resistance of an aftermarket sending unit below its lowest reading (MAYBE if you messed with the actual coiled wire which creates the resistance).  Adding reistance, yes... but reducing?  If the lowest it goes is 33 ohms, that's probably going to read less than 3/4 of a tank.  Just about what my old R/T used to show if I squeezed every drop into the tank at fill-up time.  Without finding some way to add a small amount of current back into the fuel gauge circuit to trick the gauge into 'seeing' a lower resistance, you'd be heading in the wrong direction.  That's why these mis-matched setups never - ever - read "full".

Technically, you can reduce the overall resistance in the circuit by adding a second fixed resistance in parallel with the sending unit--another path to ground for the 12v coming from the gauge. I have never tried to fix a fuel gauge/sender mismatch this way myself, but from a purely electrical engineering standpoint, it gives you more options to fudge the range of varying resistance.   

[keith88]

Any new news on this i have the same issue and am looking to fix it as well.

[lukedukem]

Any new news on this i have the same issue and am looking to fix it as well.

Hi,

Here's another gauge converter unit. I don't anything about it but, it looks like it's less expensive than some others out there.

http://www.technoversions.com/MeterMatchHome.html   

reading on that it says it will work for mopar cars for the 60s. I'm gonna buy one and see if it works.


Luke

i did get mine in the mail, but haven't installed it yet. been trying to get rid of a vibration issue in my cummins... but i will attempt it soon i hope...

luke

[fc7cuda]

Any new news on this i have the same issue and am looking to fix it as well.

Hi,

Here's another gauge converter unit. I don't anything about it but, it looks like it's less expensive than some others out there.

http://www.technoversions.com/MeterMatchHome.html   

reading on that it says it will work for mopar cars for the 60s. I'm gonna buy one and see if it works.


Luke

i did get mine in the mail, but haven't installed it yet. been trying to get rid of a vibration issue in my cummins... but i will attempt it soon i hope...

luke

Did you get the unit installed, and are you happy with the results?

[Charger-Bodie]

Tanks inc has one that works well

[Nacho-RT74]

adding resistors is a linear change, which won't change a lot the big difference. Would need somehow a logaritmic resistor... if they exist ? dunno.

[lukedukem]

Any new news on this i have the same issue and am looking to fix it as well.

Hi,

Here's another gauge converter unit. I don't anything about it but, it looks like it's less expensive than some others out there.

http://www.technoversions.com/MeterMatchHome.html   

reading on that it says it will work for mopar cars for the 60s. I'm gonna buy one and see if it works.


Luke

i did get mine in the mail, but haven't installed it yet. been trying to get rid of a vibration issue in my cummins... but i will attempt it soon i hope...

luke

Did you get the unit installed, and are you happy with the results?

Wow five years later and I can say that I haven't installed it yet. Still on the shelf. Life got in the way and I forget. Since it didn't really hinder my ability to drive the car it wasn't a need. Sorry
Maybe I can try to make time on my next seven days off. Don't hold your breath. Lol

Luke