Gas gauge goes crazy while car is moving

[mdross1]

Could not find specific info in the search function.
Our car has SW gauges the fuel sender is in non baffled tank. Full tank no problem from that point on the gauge needle flops all over the place while car is moving.Is there a trick electrically to dampen the needle or maybe a different style tank sender.
Have considered pulling the tank and baffling it but am hoping for an easier way.

[Ron61]

I had that problem with mine when I first finished it and what it was, after the gas got down a little it would slosh around and cause the sending unit to move around. I went to a baffled tank set up and had no more problems. I could have over a half tank of gas and on hard acceleration the gauge would go clear to the empty mark and back and just all over.

Ron

[olddog]

Theoretically you can filter noise out with a capacitor and a resistor. It is done all the time in other applications. The down side to a filter is that is slows down response time. In this case you do not need a fast response. With the gas sloshing around, you will never get an accurate reading until the sloshing stops, but I think you could improve the reading quite a bit.

The sending unit is a variable resistor. If I remember correctly the + voltage goes to the gauge. The other side of the gauge goes to the sender, and the other side of the sender goes to ground. I'm thinking it would be best to put the capacitor across the gauge, with a resistor in parallel. The bigger the capacitor the longer it will take it to charge up. The higher the resistor ohm the slower it will discharge the capacitor. This will slow down the changes in the gauge, as the voltage across the gauge will be more stable.

I can talk to my I&E guy and see what sizes he would try first.

[FWB]

agree with oldog...

a lot of fords in the 60's-70's had a unit under the dash that did this for gauges. was low tech bi-metal resistor. i know my 66 bird has one and they are simple to wire in. the "ohms out" is what i would be leery of as it determines your full and empty readings. btw my car does the same thing with a unbaffled tank and a SW gauge. after a few years i have learned to read between the lines.......

[mdross1]

Thanks, have heard of using resisters and capacitors but getting the right ones is part of the problem.Actually the fuel settles down very fast once stopped.And I do read between the lines kind of take an average of the sweep while flying down the highway.

[FWB]

the capacitor, i think the science is interrupting the signal momentarily to let the gauge average out the movement. of course this happens rapidly over and over again but its effective on keeping the needle movement at a minimum.

[Tim Brewer]

Also, if your sending unit/float is installed to where it moves forward and back to work, you should change it to where it works from side to side. Most tanks will allow you to do that.