The "bouncing fuel needle" on my 85 c10

[JARHEAD 11]

I have noticed on several other gm products, and especially on my 1985 c10, that the Fuel Needle bounces toward Empty as soon as I start to drive. In the Morn I can get in and the Needle will read what I expect should be in the tank, but as soon as I start up and beging to drive the needle starts to head to empty...whats the cure

[1979C20]

That is caused by the fact that our tanks have no baffles in them, just an open tank. So when you start driving, the gas pools at the back and the sending unit float drops to empty. When you stop, the needle will move all around. Because the fuel sloshes back and forth. I believe there are after market tanks with baffles in them, which will help/stop the bouncing needle. 

[JARHEAD 11]

Well thanks my friend...makes good sense. I'll just have to be good at estimation, or, God Forbid, keep it above 1/2....

[1979C20]

Well, once you come to a stop and give your tank a few seconds of no movement so it stops sloshing, the guage should show the correct amount of fuel. Does it not? Becayse if your gauge swings empty and stays than that is an entirely different issue.

[JARHEAD 11]

Actually it takes quite awhile for the guage to settle on the correct amount... usually stopped and parked. Then when I restart it is correct.....

[1979C20]

Maybe the float in the tank is sticking. New sending unit may help. Dont take just my advice tgough. Lets get some others opinions too.

[Irish_Alley]

i thought our trucks if you step on the gas it will read more than whats in it and if you hit the brakes it will go to less. thats what my 94 does anyway but are you saying it will lets say read 1/2 at start up you take off it goes to 1/4 and will stay there till you turn the ignition off to reset it

[JeffD]

I remember a post from years ago where someone actually put a resistor or something in the wire to the fuel gauge and it corrected the bouncing needle problem. I would not know where or how to find it

[SAATR]

A capacitor would likely do much to even out the voltage spikes and drops and make the reading more consistent.  I'll experiment...