I'm playing with the 71 Imperial I just picked up. The fuel gauge doesn't work.

Grounding the sending unit wire pegs the gauge full.

The sending unit is grounded to the chassis fuel line. Tests as a good ground.

Sending unit tested looks new. I pulled it and it tested good. I was just poking it with a meter so the reading was jumpy but I saw a 10-70 sweep.

Reinstalled sending unit with a seemingly good ground and the gauge sits on empty.

Pulled ground strap, cleaned chassis fuel line and reinstalled the two piece ground strap trapping a wire on each end to verify good connections. Fuel gauge stuck on empty.

I took a quick look at the float. It didn't have any fuel trapped in it but I didn't plonk it in water like I should have. However, when I stuck a camera in the tank I could see it floating.

What am I missing?

I've got a fair bit of experience with Mopar sending units (Ebody, Abody, Power Wagon) and everything you've done is sound (as you know).
I think I know the problem, especially after reading your "so the reading was jumpy". You might have a flakey internal ground and should add a wire from the sweep arm to the body. I have a couple Youtube videos showing before (w/o wire) and after (w/wire). A guy commented on how my video solved his problem. Picture taken from Moparts years ago with my text added.

The first video (no dialogue) shows the ground stabilizing once a jumper wire is hooked from the sweep arm to its body.
https://www.youtube.com/watch?v=gV_HMJa5maY

The second video shows a nice steady ground and a not jumpy 10 to 70 ohm sweep with a wire permanently soldered on.


https://www.youtube.com/watch?v=x5m71Tes0n0&t=1s

If you have it out for the mod also make sure that the signal strap, or wire, is solid at both ends. I hook my ohmmeter to the outside terminal, and open up the sender to hook the other end on the inside. Then I wiggle the strap/wire and make sure the ohms stay the same. Maybe that's overkill, just saying what I do.

Sounds like a good idea. Sadly, it is now leaking fuel around the sending unit and I was silly enough to fill the tank.

I drove it a bit today but not enough to get the fuel level below the sender. My borescope kinda greys out under the gas so I can't see the float. I'll probably jack the car up again and check the resistance between the sending unit connection and the ground strap on the chassis fuel line. That should tell me something. I just didn't want to crawl back under it again.

EBW's suggestions are viable.


I have wondered if the floats themselves may not have enough "buoyancy" to lift the arm

I have fought this battle many times over the years with different makes, models and suppliers. The last one would stop at the 3/4 mark. But if you smacked the bottom of the tank repeatedly with your hand or a rubber mallet it would go to full and act normal until you refilled the tank.
This later led me to wonder about the size of the float vs the weight of the arm 🤔

I recently went through a sending unit on a truck that sat for decades.

What I found was a corroded connection between the resistance windings and the wire for the gauge. I mean the wire riveted to the windings.

I carefully ground down the rivet so I could remove it. Then replaced it with a brass screw nut and a couple brass and fiber washers.

You'll need to pull the sender and test resistance readings at various points. Get some clip on probes so you don't need 5 hands for testing.

Note, this is delicate work. We're talking about windings not much thicker than hair.

For you old farts here, hair is what used to be on your head.

"For you old farts here, hair is what used to be on your head."




HEY ! .............. i RESEMBLE that remark !!

I'm lucky. Men in my family manage to retain most of our hair. Thinning and graying but grandpa didn't hit bald till well into his 80s.

my old man had hair on the top of his head until the day he passed.
every time we got together, which was at least several times a week, he would always look at me and say : "he, he, he...........i got hair and you don't ! ..........he, he, he.........."

Problem solved.

I had been driving the car and put a bit more gas in it. Sunday morning I stuffed the camera down the filler tube again and could not see the float. It sank.

Pulling the sending unit out again I found tiny cracks in the float. They were not visible when the gas evaporated off the float. All I could figure is that when I was wiggling and twisting the sending unit to get it out of the tank the fuel drained out of the float.

I popped a new float in the hanger and everything works as it should.

Apparently, when I stuffed the camera in the tank the first time the fuel level was low enough that the float arm had bottomed out and it looked like it was floating.

There is a plastic float that ive been using that is a direct replacement for the brass float, the plastic float is for newer jeeps

Yup, that’ll do it. I should have mentioned that as possibility but didn’t after reading “I could see it floating”.

Sending unit float weight comparison. Thought this would be interesting and a good place to post it.

hmmm............
nice comparison.
i'm ASSuming the plastic float is ethanol proof ? if so, where did you obtain it, or did it come with the sending unit ?

Agreed, but you would also need to factor in the displacement of each…if one is a bit smaller/larger than the other that makes a big difference.

They work fine for me, you guys are over thinking it. I got sick of the brass ones sinking

I agree if it floats it's weightless when it's floating.

It came with a unit, sorry can't remember from where or what kind.

I believe that is a Ford float.

See my previous remarks on buoyancy

Why would the weight make any difference? they both will raise and drop with the fuel level. I doubt one will drop further than the other both being hollow floats.

Google displacement

A heavier float, though it may float, will sit lower making the gauge read low. Now I don't know if the difference between the two matters enough to notice here. Then there is the dampening effect of the heavier vs lighter float.

The float in my 51 a a cork.

So if he plane exceeds the speed of the conveyor belt but there is a slight tailwind...

Yet another concept that eludes your grasp. What makes a plane fly is the speed of the air across the wing. the wheels have no bearing on that.

Yet another concept that eludes your grasp. What makes a plane fly is the speed of the air across the wing. the wheels have no bearing on that. [/quote}

Tell you what, how about you attempt to broaden your grasp on humor? That was simply a reference to a similar thread/ debate that went around here and was fun to watch. Just a reminder of some of the things that were said. Jeeze, you need a full disclaimer these days or some keyboard cowboy will find a way to twist your statement and attack...

Yes, one floats higher.
Quantify that.
They're on a float arm on top of the liquid. What would the difference be?
1/8 inch?
1/4 inch?

A tiny fraction of the total swing of the float arm on a relatively inaccurate gauge designed to give you a rough idea of remaining volume.

It would not make a notable difference.

Then neither would weight, as both factor into the reading. Both make a difference, whether it’s notable or not?

Only difference I can think of would be the gauge stays on full a bit longer, or drops off full a bit sooner. The other extreme would be on the empty side. A heavy float sitting deeper in the fuel, could make contact with the bottom of the tank faster and may still read there is still fuel there.

Back when I worked at the Chrysler dealership, we had a lady that ran out of gas in her new car 3 times and had it dragged back to the shop because it would run. Her old car would run a long time when the gauge read empty, but this one was actually out of gas when the gauge read empty. I fixed the problem for her. I bent the float arm so the gauge was reading empty when there was still a 1/4 tank of gas. It dropped off of full pretty fast, but she didn't run out of gas again.

The point is, the float arm can be bent to give you a gauge that reads the way you like it to.

the weight of the arm and effort required to overcome any resistance to moving can be affected by too small of a float. Think of an empty 55 gallon drum in water. It will float of course. Now take that same drum and fill it half way with gravel.
Put it back in the water, it will still float but sit lower in the water by X amount as its surface area remains the same but the weight changes.

A larger surface area would support the weight with less displacement of the water.

The size of the float has to overcome the weight of itself, the arm and any resistance it may have to moving.

my old man always "tried" to run out of gas because he always was "gonna get some gas" when the gauge got to empty, but for some unexplainable reason, he never ran out !
on the other hand, my brother ran around with a guy back in his school dayz, and slightly afterward, that thought when you get gas, you only put in a buck or two.........
many times, my little brother had to help push his buddy's car to the gas pumps, or walk to the gas station with a can and walk back when his buddy ran out !
one instance comes to mind...........
little bro, and his buddy were out with their girlfriends one night, running around consuming "adult beverages" in his buddy's car, and coming down the street past my house, they ran out of gas. [gee........what a surprise !........imagine that.........]
luckily, there is a little corner station about 100 feet from the light at end of the street [at that time, if i remember right, it was a 7-11], however, it's an uphill push !
so little brother and his buddy's girl friend get the "pleasure" of helping his buddy push his car up to the gas pumps.
at that time, little brother was dating a preacher's daughter. he was always called "Preacher Bob". [and yes, it seems all the stories you have heard about preacher's daughters are true, at least in this instance it was..... ] she didn't help push, as she was "resting" in the back seat.
so his buddy puts in 2 bucks worth, and off to take the girls home..........
after that exertion of pushing the car to the gas pumps, little brother feels kind of nauseous........
when they get to the preacher's house, he gets his date out of the car, walks her up to the front door, props her against the house, rings the bell, barfs in the bushes and leaves ! ............
not sure how many dates they had later, but the story continues.............
many years later, after little brother earns a degree in business administration, plus degrees in both mechanical and electrical engineering, he lands a job with GE in erie, pennsylvania, at the locomotive building plant complex.
on one weekend, he was in town visiting, and my old man had taken his car to the local shop for a state inspection and dropped it off the day before.
since the car was ready, and little bro was staying at my place for the weekend, we hopped in my car, picked up the old man, and off to the shop we went to get the old man's car.
when we arrived, upon entering, we discovered "Preacher Bob" was there as well..........
"Preacher Bob" had warm greetings, saying : "hi Eric ! [me], hi Jim ! [the old man] but just had a perfect GLARE for my brother !
glancing sideways at my little brother, i could see he was doing his very BEST to conceal a HUGE laugh !
after the old man paid his bill, and a general BS session was done between me, the old man, the shop owner, and "Preacher Bob", we left..........[as expected, my brother didn't partake in the exchanged pleasantries]
as soon as we got outside, and away from the shop entrance enough distance we were sure nothing we said could be heard, little bro burst out laughing, and said : "wonder if ol' Preacher Bob" remember the night i barfed in his bushes ?"
we all had a huge laugh about that, and THAT story STILL brings huge laughter today when brought up with the few remaining family members !

My ex- BIL said my sister could drive cross country on empty. But as soon as he would take the car it would run out of gas 1/2 way to the nearest gas station about 2 miles away 🤣🤣🤣🍻

Ah the internet.

About the only place a conversation about an inoperable fuel gauge turns to puking in the bushes.

Not that I've never puked in the bushes.

are you suggesting there is a story to be told ?

I can tell you why the toilet and sink are sometimes close to each other.
But the news years eve party punch appeared and tasted harmless 😱👎💥🎆🤮🤮🤢🤢😵😵

I don't remember much of it but it involved finishing off bottles of wine at a wedding reception.

Back when we were dirt track racing, I remember a few problems associated with the annual points award banquets. All of those were held at the same location. Since that was the only times I had those problems, I'm blaming the location. I have not been at that location since that last banquet I attended, and haven't had those problems since. I also quit drinking at about the same time, but that couldn't have had any effect on that....

Some how, this post has got to be related to a sketchy fuel gauge, but I'm not sure how. I know it has to be, I was responding to the discussion and on Moparts, the topics never venture off course.

" I was responding to the discussion and on Moparts, the topics never venture off course."