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Voltage Gauge Jumping Jacks

YW84U

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March 10, 2000
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City, State
BC
Year, Model & Trim Level
1991 XLT
My voltage gauge has bounced around for as long as I can remember... It actually goes with the dimming of the headlamps and changes in pitch of the fuel pump whine. I replaced both POS and NEG cables and the battery, figuring they were suspicious.

It made no difference to the bouncing / power fluctuations. But the other day, I was driving along and hit a good solid bump, and found that the gauge then became steady, and no power fluctuations! This would last a few minutes, before going back to bouncy-bouncy-bounce.....

So, I'd aim for another pothole, and voila! Gone again for a few minutes... I had been contemplating the voltage regulator or the alternator, but with this new observation, I'm not sure the cause.

Any ideas of the culprit? Any help is appreciated!
 



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I'd consider spending a "six-pack saturday" cleaning grounds.... fenderwell, firewall, wherever you can find them....

You could use a DVOM to check voltage drops - to obtain proper readings the circuit will have to be "active".
 






I hooked up a digital meter to the bat posts, and find that the voltage jumps between about 14.8 and 15.3 volts on idle. If I step on the gas, it settles at a steady 14.9 or so. Do you think a bad ground would be the suspect? It seems very consistent, both the behaviour and the voltages...

Are there any gound points on a 91 I should look at first? Looks like a rat's nets of wires under there - If you could point me in a direction, that would be greatly appreciated!!

Thanks!
 






I don't know if the voltmeter has this or not but I think that in the electic oil pressure guage (even though its fake), electric speedos, and definitely gas gauges, there is a resistor wired in that balances the movement or makes it move slower if you will( you don't want you gas guage to bounce around when you hit a bump right). Maybe your resistor has become disconnected or something. I'm not sure if it even has one, but if you can't find anything else and it still does it, its not a big deal. I know my voltage gauge will go down if I put down one of the windows, or turn on my lights. But it pops right back up.
 






Originally posted by YW84U
My voltage gauge has bounced around for as long as I can remember... It actually goes with the dimming of the headlamps and changes in pitch of the fuel pump whine. I replaced both POS and NEG cables and the battery, figuring they were suspicious.

It made no difference to the bouncing / power fluctuations. But the other day, I was driving along and hit a good solid bump, and found that the gauge then became steady, and no power fluctuations! This would last a few minutes, before going back to bouncy-bouncy-bounce.....

So, I'd aim for another pothole, and voila! Gone again for a few minutes... I had been contemplating the voltage regulator or the alternator, but with this new observation, I'm not sure the cause.

Any ideas of the culprit? Any help is appreciated!

How much is the needle moving? From what you describe it souds like the gauge is functioning properly. It SHOULD move as the load changes because the voltage is changing.
 






The dealer rigged up another ground wire from the NEG of the battery to the chassis - something about a positive loopback something or other (this was while diagnosing my no-start condition). When it bounced, it would travel about 1/8th of the guage face.

I haven't driven it since, since I'm inthe midst of a BL and changing the fuel pump. I started it up this morning, and on idle, the guage now reads bang in the middle, and does not bounce around anymore. I don't know yet what it'll do when I start driving it, but it leads me to believe that either the new ground is working, or maybe the fuel pump was creating a funny load on the electricals. It'll be interesting to see over the next few days!

Thanks All!
 






Originally posted by YW84U
I haven't driven it since, since I'm inthe midst of a BL and changing the fuel pump.

:confused: What is a BL?
 






Body Lift - I've seen others use the acronym on the board, so I assumed it was appropiate.

Not to be confused with being in the middle of a BM ;)
 






bouncing voltage guage

i've got the exact same problem, though i haven't found a relationship bewteen potholes and the bounce-
the lights pulse as well-

hey YVM80, did the extra ground fix the problem, and where/how did the dealer attach the extra ground- did he just screw it to the sheet metal?

Anybody out there see a problem with installing the extra ground?

thanks for any advice

jasonscottw
 






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