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Old 08-25-2010, 08:17 PM   #1
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Erratic, bouncy fuel gauge.

Hey. For as long as I can remember my fuel gauge made it nerve wrecking to drive. If I came to a complete stop and waited a second and I was on level ground it would read fine, but when I brake it goes up and when I hit the gas it goes down. I mean isn't there a damper on the float? Or is there a damper like a coil or inductor in the gauge itself? Just want to know which one isn't working right.

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Old 08-25-2010, 11:52 PM   #2
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Re: Erratic, bouncy fuel gauge.

Your sending unit has a "potentiometer." That potentiometer is rated at 90 ohms. When you brake and give it gas, the fuel swishes back and forth. In the tank there is a basket so that the fuel doesnt splash around that much. That basket could be broken. Or the potentiometer could be extrememly sensitive that it is sending a resistance that affects the fuel meter gauge rapidily. If it marks fine when at a stop, then dont worry to much. But if your nearly empty, the fuel could completely move to one end or the other and can suck up air which could cause you to lose power or stall. You should be happy. Mine sending unit is bad. Marks full when almost empty, marks low when full. It gots a mind of its own.
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Old 08-26-2010, 07:14 AM   #3
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Re: Erratic, bouncy fuel gauge.

A fuel gauge that fluctuates quickly is an indication of a bad sending unit. Replace the sending unit it the tank.
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Old 08-30-2010, 11:42 AM   #4
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Re: Erratic, bouncy fuel gauge.

Sounds good, thanks for the replies. BTW I think since the gauge is operated by changes in resistance (current) then the sending unit must have a variable resistor, not a potentiometer, since potentiometers control changes in voltage.
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Old 08-30-2010, 11:47 AM   #5
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Re: Erratic, bouncy fuel gauge.

my fuel guage works fine.. it kinda pisses me off when Im on a incline or decline ... u can go from 1/4 tank to full
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Old 08-30-2010, 11:50 AM   #6
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Re: Erratic, bouncy fuel gauge.

Its a 90 ohm potentimeter, just like the TPS or a volume ****.
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Old 12-09-2010, 08:10 PM   #7
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Re: Erratic, bouncy fuel gauge.

Quote:
Originally Posted by sr20fd3st View Post
Sounds good, thanks for the replies. BTW I think since the gauge is operated by changes in resistance (current) then the sending unit must have a variable resistor, not a potentiometer, since potentiometers control changes in voltage.

Correction, A potentiometer is a variable resistor. It controls the resistance.
The voltage DROP across both leads is controlled by the Resistance.

Also, Resistance is measured in Ohms, and current is measured in Amps; they are not the same thing.
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Old 12-10-2010, 02:05 PM   #8
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Re: Erratic, bouncy fuel gauge.

In every third gen I have owned the fuel gauge would move back and forth. Time to get gas when the gauge stops moving.
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Old 12-10-2010, 04:02 PM   #9
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Re: Erratic, bouncy fuel gauge.

The sending unit is not making your gauge bounce around as you drive. A failing S/U can cause erratic gauge readings but the gauge should never bounce around. The sending unit is a potentiometer, like a volume control. As the fuel moves in the tank, the float moves, so changing the "volume" of the signal from the S/U to the gauge. The changes in S/U signal are instant whenever the float moves.

The gauge was orginally built with a delay circuit that stores whatever signal level it receives from the S/U. On a healthy fuel gauge it takes about 10 seconds or more to change from E to F when the S/U is moved quickly from E to F. The problem is that your gauge is old and this circuit has failed. NAPA used to sell a repair kit for these old analog gauges. It consisted of a capacitor. The capacitor stores whatever voltage it is supplied and takes a few seconds to discharge when the voltage is changed. Connecting a capacitor, about 400microfarat I would guess, parallel to the gauge should slow the gauge's movement down quite alot. Otherwise, have your cluster rebuilt.
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Old 12-12-2010, 04:30 AM   #10
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Re: Erratic, bouncy fuel gauge.

Good call on the difference between potentiometer and variable resistor. The sending unit is in fact a variable restistor. Not a potentiometer.
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Old 01-27-2011, 11:13 AM   #11
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Re: Erratic, bouncy fuel gauge.

My guage just started bouncing around realy fast then it would stop and sit at the halfway mark for a second or two and would start going crazy again from full to empty really fast and the car isnt even moving any ideas on what can exactly be wrong?
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Old 01-31-2011, 11:47 PM   #12
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Re: Erratic, bouncy fuel gauge.

My fuel gauge does the same thing too. When I fill up my tank it'll stay up top for awhile but then after awhile of driving and braking and stopping and then going again it'll start to drop slowly and fluctuate more often. It's VERY VERY annoying as I do not know how much gas I have in my tank.
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Old 02-03-2011, 05:17 PM   #13
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Re: Erratic, bouncy fuel gauge.

Quote:
Originally Posted by ASE doc View Post
Good call on the difference between potentiometer and variable resistor. The sending unit is in fact a variable restistor. Not a potentiometer.
A variable resistor IS a potentiometer.

http://en.wikipedia.org/wiki/Potentiometer
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Old 02-03-2011, 05:37 PM   #14
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Re: Erratic, bouncy fuel gauge.

Actually, no. A variable resistor, such as a rheostat, has two terminals and controls current flow, whereas a potentiometer has three terminals and is a voltage divider. The "pot" is a variable resistor but not all variable resistors are pots.

The fuel gauge sending unit is actually a rheostat, not a potentiometer.
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Old 02-03-2011, 05:50 PM   #15
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Re: Erratic, bouncy fuel gauge.

BTW. captainchadl, your severe fluctuations are probably caused by a failing sending unit. A gauge that fluctuates with changes in geometric force(acceleration/braking) is generally caused by failure of the dampening circuit in the gauge itself. A gauge thats fluctuates sharply from empty to full, especially with the car at rest, is generally caused by poor contact of the follower with the resistor surface at the sending unit.
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Old 09-16-2011, 12:03 PM   #16
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Re: Erratic, bouncy fuel gauge.

i no this is an old thred but i have a guage that does the same thing bounces around bad if im just crusing on the highway it stay up slightly
higher,
how would i fix this clean the contacts on the sending unit??

new sending unit or put a capictor in the guage if so just tell me what wire?? cut and soder in im guessing?
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Old 09-16-2011, 12:03 PM
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