Fuel gauge floats around.

[Ronzo]

Hey guys, I am new to the site though I've been reading post on here for a little while. I just bought a sweet little one owner 86 Silverado (all original) in awesome shape. I bought the truck in Memphis and hopped in it and drove it 5 hours home to Ky. The truck has a few very minor issues one being the fuel gauge. When I fill it up it doesn't always go all the way to full then it kind o floats around between half and full at times. I can thump the gauge and it will float back toward full for a bit then float around some more. As of now I am only sing the drivers side tank because the PO said he hasn't used the passenger side in 20 years so until I drop it and clean it I am not switching over to it (assuming the transfer valve and everything works. Anyone have any suggestions concerning my floating fuel gauge? Thanks in advance for any help.

 

[smoothandlow84]

Could be a faulty gauge or even sending unit. My fuel gauge drifts a little when bouncing around, but I blame that on 80's technology...or lack thereof.

 

[chengny]

There is a pulsation dampener (a resistor actually) that bridges the two opposing coils. It's function is to control the rate of movement of the ray (needle) when the sender is generating large fluctuations in a short period of time - like going around a corner fast or slamming the brakes on. If the coil is open, or the entire ceramic plate - on which the coil is mounted - is missing, the gauge will bounce around and provide erratic readings.

The pivot pin on these gauges (1965 -1990's) is free to make full revolutions in either direction. Although people use the term "pegged out", there are no pegs on either side.

Some images of a gas gauge out of a 1986 K30 to help explain:

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

And this - from someone who knows a lot more about gauges than I:

Don’t Resist Using The Resistor

For some unknown reason, folks do not like to put the resistor on the back of the gauge; maybe because they lost it or they do not think they need it. This type of ceramic shunt-type resistor was phased in to replace the wire-wound resistor and wafer board found on earlier models. The wafer board isolated the resistor from the gauge housing. They both do the same thing by controlling how fast the needle sweeps across the gauge. Think of taking a turn in your Chevy and the needle moving every time! This makes it tough to get an accurate fuel level reading. If the resistor is not in place on an original or AC Delco replacement gauge, the gauge will not operate properly.

 

[chengny]

Never mind the post directly above - that guy is an idiot and no one even likes him. What he is talking about only applies to when the vehicle is in motion and is entirely unrelated to your issue.

If you can get the gauge to read better (or even just differently) with a local tap or slap...I would assume it's either a bad connection in the harness connector, a loose fit at the clips in the cluster or maybe you just have an old broken gauge.

A good start when trouble shooting a hinky gauge is to check the sender ground lead. Make sure you have a clean tight connection on both ends:

You must be registered for see images attach

You must be registered for see images attach

You don't need to pull the bed, just reach up and give the wire a good vigorous jiggle. Sometimes that will make everything alright for another 5 years.

 

[smoothandlow84]

Lmao..."give the wire a good vigorous jiggle". Sounds like good ol 80's technology ...lol. seriously though, thats a great idea. I have chased several grounding issues on my square. After 30 plus years, corrosion, vbrations and the elements can be detrimental to electrical connections.

 

[Ronzo]

thanks for your replies. Now if I ever get spare time ill check out my grounds.

 

[Grit dog]

Never mind the post directly above - that guy is an idiot and no one even likes him. What he is talking about only applies to when the vehicle is in motion and is entirely unrelated to your issue.

Old thread I know, but that schit is funny!
Besides, the post above is the problem I am having and now I know what's wrong and another thing on my list when I pull the interior apart.
Thank you for the info! (if you're still around)