gas gauge goes back an forth when im moving.

[sidschev]

im wondering if its possible to put a newer style sending unit in to alleviate that bouncing needle ?

 

[Grit dog]

There is a resistor you can add. I found a thread about it on this forum somerhwere. Haven’t done it yet. But seems that’s the fix.
Thst said, despite the gauge bouncing, it’s dead accurate in our 86.

 

[sidschev]

hummm mush do research thank you

 

[Wallace6]

All the later models squares seem to be fairly accurate, don't know what changed but my 87 and 89 seem fine, my 73 moves all over, my early Camaro did the same.

 

[Randy and Easton]

We just put a brand new gas gauge from LMC in last week as we concluded the resistor was bad on the old gauge. Had new sending unit about a year ago and it worked fine, then one day parked about 1/4 full when tank was full and went down from there.

New gauge is maybe a tad overly accurate. Still checking it for accuracy but it does not start the big movements till it’s about 1/4 left in the tank. Slow to get under 1/2 tank making Easton think he is getting good mileage (not, maybe 10 MPG?)
Anyway, the movement doesn’t start till below 1/2 on gauge.
I really don’t want to take cluster out again and add another resistor at this point… I told him to fill up at 1/4….

 

[andybflo]

If you want to slow the swinging on an older fuel gauge, you add a capacitor, not a resistor to the signal wire.

The device is a varistor, essentially. So, if you change the resistance, it'll change what you display on the gauge. If you add a capacitor, it'll smooth the peaks and valleys (what you see as swinging) on the gauge. New gauges (pre-computer) have said capacitor in them, post-computer it's waveform generated to be smoothed.

I usually install a 1.5f, 15v on customer cars when we do a restomod. If you want even less responsive more farads, more responsive fewer farads. They're available from Amazon or anywhere else (Digikey, Mouser, etc) for a few pennies a piece (buying small quantity, unit price will obviously go up)

On my personal square? It waves to me on its way down. My wife laughs whenever we take the truck out. I haven't done it yet on most of my old cars. Some there's no point (like the Square; I have two tanks, and an average is just fine, thanks), some I just haven't restored them yet. I'll do it when the cluster is out and getting worked on.

Feel free to experiment. You won't break it, as long as the voltage is 15v or greater. You don't want that thing going bang under your dashboard. No harm, just a really loud pop.

 

[79SierraClassic]

The reason the newer unit don't have the swings that the older units do, is when the units went to fuel injected, a baffle was installed into the fuel tanks to keep more fuel around the intank fuel pump. This helped reduce the fuel movement reducing fuel gauge swings.

 

[sidschev]

If you want to slow the swinging on an older fuel gauge, you add a capacitor, not a resistor to the signal wire.

Thanks ill look into this as well. i dont have my dash out so im researching as much as i can. i have dual tanks but i want to remove the after market tank. i just dont like it.
i have a bunch of electronics stuff so just need to research more. I do not want anything to go boom unless i tell it to.

 

[andybflo]

The reason the newer unit don't have the swings that the older units do, is when the units went to fuel injected, a baffle was installed into the fuel tanks to keep more fuel around the intank fuel pump. This helped reduce the fuel movement reducing fuel gauge swings.

That's actually not the reason.

Modern gauges (like OBD-II) don't actually use a variable resistor direct to a gauge in many/most cases. They're driven off a CANBus, and they're PWM. That's even how the Dakota Digital gauges run; analog inputs to a control box, PWM out. There's a factory hysteresis setting for any gauge that's built into your body control module governing that input.

You can even change it to zero while editing that BCM's programming, and watch your oil/fuel/whatever gauge bounce around, just like in your square. It actually has value to remove that damping factor (or read the real-time-data) to someone trying to diagnose a problem. They just make it "pretty" for the soccer mom driving a Tahoe so she doesn't see her fuel gauge hopping around.

The baffle is often times not even where your fuel gauge float is located. The sump there would give an inaccurate reading, and frequently have collision issues with the walls that make the baffle up. For example, on the German SUV and Sedans that make up my wife's/my daily drivers, the sending unit is all the way across the fuel tank from the pump units. Ditto for many modern GM and Ford cars. Separate assemblies in general.

I run '87 tanks (sump'd and baffled) for all my LS swap Squares (including mine.) Use TBI sending units, with more modern Walbro pumps.

They still bounce everywhere while driving/stopping.

 

[Randy and Easton]

Well, now Easton says the sending unit is not accurate. Gauge almost empty and he put 14 gallons in last night so still have 6 and the gauge is almost empty. He says after he fills it up stays above full for awhile before falling…..
sender (LMC) was done a few years ago when he had truck apart. Guess we will pull the bed this weekend and drop a new sender in…
The gift that just keeps on giving

Randy and E

 

[mibars]

Fuel gauges in many cars use some sort of a dampener on a needle, it turns like it is in molasses, I wonder if back in the day gauges had the dampening effect and it simply wore out/dried out?

In my 1990 gauge is slightly changing position when accelerating and slowing down, but that's in a range of half a mark, or 1/16 of a tank.

 

[Randy and Easton]

This is a brand new gauge from LMC (not saying much) last one blew the resistor and was stuck at 1/4… I loathe getting another resistor and fixing old gauge to see if it’s any better than this. Working in the cluster is just not my favorite thing…
We did bench test new gauge with new sending unit and it was completely accurate with the new sending unit so Saturday’s project is on the books

 

[David King]

My gauge would stop at half a tank when I know it was full and as I drove it and the gas emptied when it got to half a tank the gauge would start down to "E". Replaced it with one from LMC, problem solved, steady as a rock.

 

[Randy and Easton]

Replaced gauge or sender @David King

 

[RecklessWOT]

it bounces and floats around, but once you're sitting still or just cruising steadily on flat ground it will give an accurate reading. Not the best system for a split second glance, but if you know your truck well enough you will know how much fuel you have. Only ever bothered me a few times in my life- I used to have a very steep driveway and would wake up late and leave in a hurry, assuming I had enough gas to get to work. Once I left the driveway I realized I had to stop for gas, making me late. Otherwise I would've thrown in a few gal from the can in the garage. But overall in real life it's never been a real problem, just a quirk of owning one of these old rigs. No big deal in the scheme of life