Fuel Sending unit adjustment

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jhdeval

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My gauge reads very low. The gauge works and the sending unit works. I tested the sender outside the tank and the gauge will show full when float is at the top and empty at bottom. So I am guessing the sending unit needs to be adjusted. How so you adjust it?
 
Bend the arm slightly to fine tune it. Better to show low/empty with a bit left in the tank.
 
Yep the float arm.
 
Mine does a similar thing. Reads full, when full, but drops very quickly (10-15 minutes of driving) to between empty and 1/4 and stays there for ever until the fuel level reaches that point.
It's a brand new tank and sending unit, what a pain in the ***.
 
jhdeval said:
My gauge reads very low. The gauge works and the sending unit works. I tested the sender outside the tank and the gauge will show full when float is at the top and empty at bottom. So I am guessing the sending unit needs to be adjusted. How so you adjust it?
Click to expand...

I just replaced a factory sender with a Spectra Premium sender. On both the old and new units, the float is right next to the fuel pickup tube in the "empty" or down position. If yours is a lot higher than that, bending the float arm might solve the problem.

The symptoms you describe are similar to my old sender's, due to a cracked, gas-filled float. It always read below 1/8 tank, but the sender delivered the right range of resistances when the float arm was moved through its range of motion. Make sure the float in your sender actually does float and hasn't filled with gasoline.
 
The sender should show no less than 9.6 ohms resistance at full and 73 to 78 ohms at empty. The arm has stops that limit its travel. Bending the arm might change the 1/4, 1/2, other, position but the ends wouldn't change. The problem could just as easily be the gauge.
 
ALL...MY post "Spectra or Quanta" (http://www.forabodiesonly.com/mopar/showthread.php?t=156759)
is the result of my research into everything being described in this thread. reading empty or mid tank or 1/4 tank after driving for 10 mins etc etc etc....

what it all breaks down to is the MAKER of the sending unit SPectra buys them from CHINA ( go figure) and the Chinese have copied the stock sender almost exactly...leaving out ONE very important component. Stock senders are all NON LINEAR variable ground, hence variable OHM sending units. This allows for much closer readings at each height along the path of what amounts to a "ground potentiometer" attached to the float arm that sends the "signal" to the gauge. the NON linear is a perfect match..trouble is NO ONE MAKES THEM ANYMORE. SPectra makes LINEAR senders and the gauges are all made for NON linear variable grounds...the MISMATCH is where the fuel reading idiocy comes in. The gauge is expecting a nice smooth signal from the sender and what it gets is a series of abrupt changes both inside and outside the acceptable ohm ranges of 10 & 73 this causes the gauge to go crazy and show whatever the sender is sending at the moment which on a linear gauge could be ANYTHING...... linear means a straight path from empty to full and fuel tanks do not act like that...fuel sloshes around hence the gauge sloshes around or goes up & down randomly...this random movement causes random OHMS to be sent to the gauge whic in turn being all over the board hoses the "smoothness of the gauges ability to give a proper reading of whats in the tank...NOT the ARM, NOT the FLOAT, ( always check the grounds ) not the gauge, not the pick up tube...if you have a "new" unit it is likely made by SPectra and it is likely linear and it will not read correctly unless you have a corresponding gauge that tolerates LINEAR movement from the sender... all of the descriptions of "what could be wrong" are all correct ASSUMING the sender is stock, non linear performs to specs, they are equally incorrect given that the sender has been replaced with an aftermarket one and is set up to be LINEAR .
N joy!!
 
What ever you say I guess. I haven't seen any difference in the resistance winding in aftermarket senders but i haven't seen them all.
i do know that any sender will supply a constantly changing signal to the gauge due to slosh while driving. The gauge pointer movement comes from heat generated by the resistance. The temperature of that bi-metal will not change that fast so it shows a general or average position.
 
The Spectra sender I bought last month was made in Mexico, according to the label on the box.

The thing about fuel senders is that they sense the level of fuel in the tank, not the quantity, because the sensor floats on the fuel. The problem with gauge/sender linearity in our A-bodies has a lot to do with the shape of the gas tanks. Fuel level in those tanks does not have a linear relationship to fuel quantity because the bottom part of the tank holds the majority of the fuel (top part is smaller to fit around the spare tire well). When you've used the the first third of the fuel, the fuel level is actually half or less the level of a full tank. That's why a "linear" sender and gauge will indicate a fuel level that is lower than the quantity of fuel remaining in the tank, just as we see with these replacement senders. The OEM "non-linear" sender wiring (plainly visible in my OEM sender) was probably engineered to correct gauge readings for the shape of the fuel tanks.

But, then, what do I know? O:)
 
yarcraft91 said:
The Spectra sender I bought last month was made in Mexico, according to the label on the box.

The thing about fuel senders is that they sense the level of fuel in the tank, not the quantity, because the sensor floats on the fuel. The problem with gauge/sender linearity in our A-bodies has a lot to do with the shape of the gas tanks. Fuel level in those tanks does not have a linear relationship to fuel quantity because the bottom part of the tank holds the majority of the fuel (top part is smaller to fit around the spare tire well). When you've used the the first third of the fuel, the fuel level is actually half or less the level of a full tank. That's why a "linear" sender and gauge will indicate a fuel level that is lower than the quantity of fuel remaining in the tank, just as we see with these replacement senders. The OEM "non-linear" sender wiring (plainly visible in my OEM sender) was probably engineered to correct gauge readings for the shape of the fuel tanks.

But, then, what do I know? O:)
Click to expand...

So what you imply is if the tank was filled to the max, the sender would remain at the upper stop for a very long time. The gauge would show full until the float begins to drop away from the upper stop. I can agree with that. You will use the first 2 or 3 gallons before the guage leaves the full position.
If you set up and calibrate a gauge to the target ( dots ) on the screen you'll find the needle stops allow the needle to go beyond the full or 10 ohm target.
 
RedFish said:
So what you imply is if the tank was filled to the max, the sender would remain at the upper stop for a very long time. The gauge would show full until the float begins to drop away from the upper stop. I can agree with that. You will use the first 2 or 3 gallons before the guage leaves the full position.
If you set up and calibrate a gauge to the target ( dots ) on the screen you'll find the needle stops allow the needle to go beyond the full or 10 ohm target.
Click to expand...

Yep- I see the same. My gauge is pegged way over full until I burn 4 gallons, then drops all the way to 1/8 tank as I burn the next 6. Haven't tried running out the last 8 gallons to see how the gauge behaves. :)

That's not how the gauge behaved with my old sender (before the sender quit), but it's still useful.
 
yarcraft91 said:
Yep- I see the same. My gauge is pegged way over full until I burn 4 gallons, then drops all the way to 1/8 tank as I burn the next 6. Haven't tried running out the last 8 gallons to see how the gauge behaves. :)

That's not how the gauge behaved with my old sender (before the sender quit), but it's still useful.
Click to expand...

I dont believe the sender is the fault. If you open that fuel gauge you will very likely find the bi-metal responder has a bow in it at room temperature. That came from being overheated and probably happened when the previous sneder died. A lot of speculation really but zero resistance for any length of time will cook the bi-metal. Due to how that strip is attached in a angled slot of the needle, the bow makes geometery wrong and the needle moves a very long distance rather than a short distance. To just go in and straighten it again doesn't fix it either. The temper of the metal is gone. Also if the insulation on that winding is black it will crumble when touched so it really just cant be fixed.
 
Ok let me weigh in on this a little. My sender has been replaced not because the old one died but because the gas had turned in the tank and I would sooner replace it then try and reuse it.

The gauge actually reads pretty accurate it was just a hair low I replaced the tank yesterday and I had just about 6 gallons which in my 18 gallon tank is 1/3 of a tank. The gauge read a little lower then it should. It should be right on the last line. I do realize bending the float arm is changing the reading coming from the sender but just like your toilet float its all about that reading.

Redfish you are probably correct that the resistance reading in the gauge is off versus the sender. Yarcraft91 I do understand what you are saying and on an electronic/electric point you are correct if the gauge was not mechanical. If I had an electronic gauge the needle would be all over the place but that is not the issue.

At any rate I bent the arm slightly and the reading is correct now. The worst thing that can happen is I bend it straight again I only bent it very slightly.
 
the float should touch or bounce against the bottom of the tank. The stop is the empty reading regardless. So the first gallon or or 2 would never move the float or the empty reading.
 
RedFish said:
I dont believe the sender is the fault. If you open that fuel gauge you will very likely find the bi-metal responder has a bow in it at room temperature. That came from being overheated and probably happened when the previous sneder died. A lot of speculation really but zero resistance for any length of time will cook the bi-metal. Due to how that strip is attached in a angled slot of the needle, the bow makes geometery wrong and the needle moves a very long distance rather than a short distance. To just go in and straighten it again doesn't fix it either. The temper of the metal is gone. Also if the insulation on that winding is black it will crumble when touched so it really just cant be fixed.
Click to expand...

Dunno- the failure in my sender was that it always read 75 ohms resistance (empty), because the float sank. But, the gauge has been passing current for 44 years and things do fatigue.

I'm planning to pull the instrument cluster this fall/winter and have all the gauges rebuilt at a shop that specializes in such things. I'll ask what they find in the fuel gauge, probably also ask them to disable the voltage limiter in that gauge and install a solid state regulator on the printed circuit board.
 
"At any rate I bent the arm slightly and the reading is correct now. The worst thing that can happen is I bend it straight again I only bent it very slightly."

Yea....sometimes its just that easy.

You know your car is old and you can expect it to act that way.

Just fill her back up when you get to 1/4 and you'll be fine like wine.

Take care.....now back to the scientists and their slide rules.....

Mop
 
yarcraft91 said:
The Spectra sender I bought last month was made in Mexico, according to the label on the box.

The thing about fuel senders is that they sense the level of fuel in the tank, not the quantity, because the sensor floats on the fuel. The problem with gauge/sender linearity in our A-bodies has a lot to do with the shape of the gas tanks. Fuel level in those tanks does not have a linear relationship to fuel quantity because the bottom part of the tank holds the majority of the fuel (top part is smaller to fit around the spare tire well). When you've used the the first third of the fuel, the fuel level is actually half or less the level of a full tank. That's why a "linear" sender and gauge will indicate a fuel level that is lower than the quantity of fuel remaining in the tank, just as we see with these replacement senders. The OEM "non-linear" sender wiring (plainly visible in my OEM sender) was probably engineered to correct gauge readings for the shape of the fuel tanks.

But, then, what do I know? O:)
Click to expand...

NOT a SLAM just a sharing of facts OK?

OK the linear vs NON linear electronic property of the variable ground sending unit HAS ZERO to do with the shape of the tank. ALSO the engineers at Chrysler accounted for the shape of the tank and placed the sender and shaped the sender to read the tank as it was designed with the spare tire indent, width height and depth included.

ALSO from the MR. Wizzard science tv series in the 50's & 60's to Bill Nye the science guy 70' & 80's tv series will all tell you, the shape of the container of a liquid has no bearing on how full or empty it is!!! The indent at the top of an a body tank ONLY displaces a certain amount of liquid residing in the tank. Therefore the sender is shaped to account for that so that the half tank mark is exactly where it is supposed to be. ANd given the size of the indent, I am certain that the half full mark is well below the physical middle of the tank... c'mon guys...do you REALLY think that was not considered when this tank and sending unit was being engineered? GEEZE

The linear vs non linear property of the sending unit is all about WHAT KIND OF SIGNAL is being sent. The signal from the sender needs to match the signal that the gauge can accept to properly show the level. The gauge and the sender MUST BOTH be either linear or NON linear, they MUST match, or your readings will be way off!

THE TROUBLE IS the primary re-popper of sending units makes ONLY LINEAR sending units ( not equal to OEM stock equipment, which was NON linear) and the GAUGE manufacturers today MAKE gauges
that are pretty much ALL NON LINEAR. HENCE THE GREAT MISMATCH causing all the erroneous fuel readings.

PLAIN & SIMPLE the aftermarket sending units are NOT compatible with the aftermarket gauges!!....if you have a decent stock sending unit, your stock AND your aftermarket gauges will work perfectly as designed....because the stock senders are NON LINEAR JUST LIKE the aftermarket gauges and the stock GAUGES...THEY MATCH!!

You cannot, with any degree of success, simply MIX & MATCH linear with non linear...they must match or they just don't work as designed and your readings will be all over the dial.

AND YES it does register the quantity via the hash marks on the gauge..and the position of the float and the corresponding position of the variable resistance ground, Hence. if you have a 15 gal tank, half way is 7.5 gallons a 1/4 of a tank is 3.75 gallons, 3/4 of a tank = 11.25 gallons and so on..... so the shape of the tank means nothing, because it is accounted for with the shape & position of the sending unit...savvy? NO fuel gauge has ever been 100% exact but if you are reading 1/8 of a tank and you still have better than 8 gallons in there....that aint just NOT exact that is WAY OFF !!!

NOT exact is about a gallon to a gallon & a half....Most people that run out of gas do it because they ride on E for too many miles, typically it is not the fault of the gauge but more the fault of the NUT behind the wheel

I have had 18 A body's in my life and NOT ONE of them with a stock gauge and sender has ever registered anything like what you are describing ..... " When you've used the the first third of the fuel, the fuel level is actually half or less the level of a full tank."

The NON linear wiring in an OEM sending unit corrected nothing, it was simply wired to be MATCHED to the gauge!!! DO you REALLY THINK IN THE 1960's they even considered designing a sending unit that electronically "corrected" anything? Hell when you parked on an angle in the driveway the gauge read something completely different than when you were on a level surface!! If that sending unit corrected for the level of fuel in the tanks how the hell did the gauge read a different level in the driveway?.... There was NO "corrective" sending units back then.....you've been readin too much RUBE GOLDBERG LOL
 
66cuda said:
I have had 18 A body's in my life and NOT ONE of them with a stock gauge and sender has ever registered anything like what you are describing ..... " When you've used the the first third of the fuel, the fuel level is actually half or less the level of a full tank."
Click to expand...

My A-body does register like that. Just my luck, huh?
 
The gauge isn't calibrated to the hash marks. There are tiny target dots on the perimter of the screen and also notches in the rim of the can that are used before the screen is installed.
Why people run out of gas in these cars is more often a fault in the sender. The long sender moves more so it wears more. Eventually the sliding contact becomes more like a fish hook. it'll catch the resistor winding and hang there forever and ever amen.
the shroter sender has a nearly closed half moon shaped resistor housing. Dirt collects in the bottom of that housing until the sliding contact cant get to the empty position.
The gauge will show something like almost an eigth of a tank while you run out the last drop of fuel.
please remember that I didn't design any of this crap, I just deal with it.

View attachment S6304209.jpg
 
The OEM (?) sender in the foreground of your photo looks like the sender I pulled from my tank last month. My OEM sender looked very clean after 44 years bathed in gasoline- just a trace of surface rust here and there. There was a crack in the brass float, which was full of gas, apparently why mine quit working.

What brand of sender is the one in the background of your photo? My new Spectra sender has a very similar rheostat, but differs in some other details, e.g., has a plastic float.
 
I dont know who made it. I can only tell you I bought it from a ebay vendor named vansautoparts. Its removed because I blew the sock off it with compressed air ( DOH! )
While I was calling every part store in town seeking a new seal for the reinstall I learned that those other senders that came with a plastic float now come with no float at all. A new brass float is sold seperately ( where available ).
By the way.. The float on that long sender could bounce against the bottom of the tank.
 
Yes- I expect the float on my OEM sender bounced on the bottom of the tank. It is dented where it also cracked. My new Spectra float came from NAPA, float and sock installed.
 
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