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