Weird fuel needle flux

[DennisG01]

I have never seen or read about this before! Any ideas?

OK, so the tank was just about empty and I started off the fill up. On the way there, I notice that the needle would swing up (clockwise) as I braked - as if in relation to the momentum caused by slowing down. The harder I stopped and the longer I took to stop, the higher the needle went - one time going completely past "F" to about the 3 o'clock position. I put a couple gallons in and it still did the same thing. Filled it up, it's fine. Have about 75 miles on it since the fill up and still fine.

Making a guess, it's almost like the float arm has lost it's "balance" and the stopping force is causing it to swing/rise.

[Warren96]

Ideas ? Yes the ground wire coming out of the tank could be loose at it's grounding bolt. The sending wire could be loose from the tank to the gauge. If I was a betting man I would say the grounding bolt, or the bracket it bolts to is corroded. Basicaly the connection anywhere between the sending unit ground at the tank, up thru the sending unit and thru the bulkhead connector behind the dshboard to the gauge, could have a loose connection. I hope this helps!

[DennisG01]

Ideas ? Yes the ground wire coming out of the tank could be loose at it's grounding bolt. The sending wire could be loose from the tank to the gauge. If I was a betting man I would say the grounding bolt, or the bracket it bolts to is corroded. Basicaly the connection anywhere between the sending unit ground at the tank, up thru the sending unit and thru the bulkhead connector behind the dshboard to the gauge, could have a loose connection. I hope this helps!

The problem stopped after I had a full tank. Wouldn't a bad ground mean the problem would continue?

This just seems different than the other threads I've read over the years about grounds. I dunno, maybe not.

[SmithvilleD]

Wouldn't you guess it's fuel movement related to the braking? When the tank's full, there's little room for fuel to slosh forward & back.

My truck's fuel level sender was hinky when I bought it. Replaced it with one from LMC truck. That corrected the "all the time" fuel gauge movement; but there's still a fair amount of gauge movement once some fuel is run off, that seems to correlate with acceleration or stopping.

[SmithvilleD]

I cleaned all the chassis & engine grounds before my engine went in, as well as using KopperShield on all the electric gauge engine senders. However I still occasionally see temporary gauge movement when switching on something that draws considerable current.

To me, this suggests some of the dash or other grounds still aren't at the same voltage potential.

[Burning Oil]

Thats actually fairly common. All mine have been the dirty or varnished sending unit. The risitor/coiled wire on the sender gets all fouled.

[DennisG01]

I've always had the movement due to fuel sloshing, but it never moved more than about 1/8 tank up/down. All of sudden it will now go from empty to WAY, WAY, WAY past full - the needle went completely horizontal, point to the right.

Now that the tank is full, it won't swing - other than that little bit it's always done. Since it's not doing it now, doesn't that negate electrical issues?

[Burning Oil]

I can only say on the last three trucks that had those symptoms the problem was what I said above on those trucks.

[DennisG01]

I can only say on the last three trucks that had those symptoms the problem was what I said above on those trucks.

Sorry, missed your post. So you've seen the gauge go from empty to way past full?

The resistor being fouled up/bad is good idea. If there was a bad spot, it might be giving off a higher resistance value. That would explain why it's not doing it now - the arm is past the "bad spot" on the resistor. One would think it just wouldn't work, but who knows. I'll have to check to see if I have some type of access to the sending unit. I seem to recall someone doing this recently on this forum, but I can't find it via the search. I'll check Chilton's.

[Burning Oil]

I know how you feel. On the trucks I worked on one could be cleaned up and worked great after, the other 2 needed new sending units.