Why does the fuel and oil pressure gauge needle wobble/shimmy?

[redfishsc]

I've driven several 96-99 trucks and Subs/Tahoes that all had the same instrument panel, and almost invariably, the fuel gauge and oil pressure gauge will wobble/shimmy when it's running.

Also, the fuel needle usually wobbles more than the oil pressure.

I noticed on my current 99 Sub (at least, the one that's running lol) that installing a brand new battery and alternator reduced the amount of wobble a HUGE amount. The oil pressure needle doesn't hardly wobble at all now and the fuel gauge just has a tiny vibration. When the alt went out and took the old battery with it, I was shocked to see how much those gauges stabilized when I replaced the alt/batt.

I have not driven a diesel GMT400 so I wouldn't know if those have similar problems.

 

[John B]

I replaced the battery but it did not make a difference. The alternator is still functioning fine, so I have no intention of replacing it. I just figured it was 17 year old technology. My volt gauge also moves with the turn signal, but I just got used to it. Maybe someone has a solution...

 

[redfishsc]

In my experience, the voltage needle will twitch with the headlights when the alternator is only barely charging the battery. I'm not an electrician but it seems like the alternator might be reading a reasonable voltage but just isn't putting out its rated amperage.

 

[Nathaniel2g]

They get old and worn out. Usually the fuel needle moves a lot more due to how much the fuel moves due to vibration and little bumps. That needle is reading off the sending unit's arm.

 

[jkeaton]

Cause old trucks......

 

[jcp5252]

I haven't tried this yet but I plan to soon.

http://www.gmt400.com/threads/how-to-fix-bouncy-hummingbird-fuel-gauge-needle.15139/

 

[big_mike]

I just took my cluster out for a messed up fuel gauge. I bought a new stepper motor off eBay for about $40. Haven't got to test it yet. I also replaced my pump assembly at the same time. So I won't for sure know which item fixed it but I'll know if neither did, lol. Mine was bouncing, vibrating and reading wrong. It was random as to how it would act which is why I first ruled out the sender. When I replaced the motor in the cluster you could spin the pin the needle rides with your fingers and it would just keep spinning. The new one is tight, so I'm hoping this fixes it. I also had low fuel pressure and rough idle which is why the pump went in.

I opted for the motor replacement over the injecting the stepper motor because I felt like that's not a fix, just a bandaid.

 

[Eskimomann209]

If this ends up working a link to the stepper would be great..
I’d Be excited to swap both of those out to alleviate this annoying issue.