Fuel Gauge Jumpin Around

[metal chevy]

Bought my truck (82 k20) a couple weeks back and one of the problems is that the fuel gauge doesnt really work. The needle goes up when I put gas in it but bounces around and doesnt stay in a certain place. It does when I'm accelerating, braking, idling, basically all the time when its running. It does it for both tanks. I'm not sure if its the gauge itself, a sensor, or what. Anyone know whatsup? Thanks.
Posted via Mobile Device
Posted via Mobile Device
Posted via Mobile Device

[tucsonjwt]

In my experience, aftermarket sending units (Spectra brand) cause the gas gauge to move with the motion of the vehicle (acceleration, braking, turning, etc.) OEM sending units will not do this. OEM units are about $140, aftermarket units are $40. I believe this has to do with the sensitivity/quality of the resistors in the sending units, but I am not an electronics expert. My gas gauge is accurate when the truck is at rest.

[bigd65]

They all do it, its because the older trucks did not have baffels in the tank, so when the gas sloshes around so does the needle

[motornut]

Originally Posted by tucsonjwt

In my experience, aftermarket sending units (Spectra brand) cause the gas gauge to move with the motion of the vehicle (acceleration, braking, turning, etc.) OEM sending units will not do this. OEM units are about $140, aftermarket units are $40. I believe this has to do with the sensitivity/quality of the resistors in the sending units, but I am not an electronics expert. My gas gauge is accurate when the truck is at rest.

X2 ,and I grounded the cluster didn't help,spotted a spectra tank figure thats the prob stopped lookin

[metal chevy]

That would make sense, but this just seems excessive. My dad had a 76 and it never did it that bad in his. Ill record a quick video tonight and post it to show exactly what I mean, I don't think I'm explaining it good lol.
Posted via Mobile Device

[tucsonjwt]

On the three squares I have owned, the fuel gauges worked properly (no bouncing around) on all 3 of them, until I replaced the original sending units with aftermarket Spectra units. In my current truck, it turned out what I really needed was a new gas gauge, not new sending units - if I had kept the original sending units then I would not have the bouncing gauge problem.
If your truck is standing still for a period of time, say 5 minutes, and the gauge is still bouncing, then you probably have a different problem.

[motornut]

Originally Posted by tucsonjwt

On the three squares I have owned, the fuel gauges worked properly (no bouncing around) on all 3 of them, until I replaced the original sending units with aftermarket Spectra units. In my current truck, it turned out what I really needed was a new gas gauge, not new sending units - if I had kept the original sending units then would not have the bouncing gauge problem.
If your truck is standing still for a period of time, say 5 minutes, and the gauge is still bouncing, then you probably have a different problem.

this is my 5th square but stripped blocks/parts out of others
never had it happen before
was one of the first things i looked into
hmm if the gauge is the same maybe I should try one from the later truck like 87?
on a side note when i change them (sending unit)i bend the arm of the float up to keep more gas at the end of the tank then when it's reading over full,why?
Less chance of a frozen gas line,and i'd rather think i got an emergency $10-20 bucks left on empty then not LOL
and doing that dosn't bother the gauge either

during high school i put a switch that shorted the sending unit to ground this made the tank read empty
people seemed to find a couple of bucks for that drive home,didn't bother it either

I just got an idea.....if i short it and it still bounces then it's something else

[metal chevy]

I went out and drove it around the block. I tried to take a video with my phone but the thing was such crappy quality you cant even tell whats goin on lol. But anyways, the needle does stay in one place at idle, its just when i start to drive that it starts to bounce around. It seems to float around where my actual fuel level is. Like itll go a little below, then bounce ahead by a little, then rinse repeat.

[tucsonjwt]

Your symptoms point toward an aftermarket sending unit diagnosis. The gas gauge will bounce around the actual level of gas in your tank, and will settle down to a steady accurate fuel level when the vehicle is not moving for awhile. So, for about $300 and a day or two working on your back, you can fix this with two new Delco sending units.

[hatzie]

The C2 Corvette guys damp the air core gauge with a Silicone Gel.

C2_fuel_gauge_and_sending_unit.pdf