[chross12]

While I was waiting on a red light to change, I noticed He tach bouncing every now and then. Performance hasn’t changed? I had some issues with the alternator and battery which I replaced both. Volts are good? Not sure 🤔 if I should be concerned? Thanks to the experts for their responses.

[chris12]

someone posted that it could be a ground wire? Other posts say its annoying but not to worry.

[chross12]

well the tach issue is getting way worse. Not only at idle but also driving down the road it bounces so frequently that its hard to discern actual RPM. back to the shop i guess... any suggestion for a fix?

[Atlas24601]

Can you feel the engine RPMs actually changing or is it just the tach bouncing?

[Chevyman2]

Had that happen in Ls3 was one of spark plugs changed and tach stopped bouncing.

Edit: This occurred at idle only

[laynlo15]

Mine does it, not just a idle. Rev to 3000 and still does it.

[chris12]

Thanks for the response. I can feel the rpm progressing up as i accelerate of course. But as long as it's not a potential pitfall, then im ok. Laynlo15 ty

[JaxChris]

Mine is in the shop for 4 weeks now waiting on GM TAC to figure it out. Whenever the voltage drops to 12.5 the cluster and HUD get irratic when accelerating and power is reduced (after 26k miles you can feel the difference). The car has 27.1k miles on it, but 1100 miles have been put on it by the dealer between the many visits it has had there. While I equate it to a 10% loss in torque, it is probably closer to 20% since the acceleration time from 40-60 or 60-80 is about 1.5 seconds longer from the same throttle positions. Instead of 4 secs, it is about 5.5 secs. Again, this isn't even WOT, just part throttle which causes a small downshift to aid acceleration. At WOT there is no point in looking at the dash because the whole time it is bouncing from 1k-7k RPM's.

Last call I got was that they are replacing the cluster -- that's it. Not the HUD as well, not the ECU, not verifying any of the engine/trans or ECU/BCM grounding points. But they are waiting for a cluster to ship.

Others have said bad grounds, bad ECU or both was what had been replaced when it finally went away. Really getting tired of being teased by VW TDi owners about having constant loaner cars/trucks and never bringing my own wheels to work. I've damn near driven the entire lineup and every length of Silverado in the past 18 months.

[Johnwon]

Originally Posted by JaxChris

Mine is in the shop for 4 weeks now waiting on GM TAC to figure it out. Whenever the voltage drops to 12.5 the cluster and HUD get irratic when accelerating and power is reduced (after 26k miles you can feel the difference). The car has 27.1k miles on it, but 1100 miles have been put on it by the dealer between the many visits it has had there. While I equate it to a 10% loss in torque, it is probably closer to 20% since the acceleration time from 40-60 or 60-80 is about 1.5 seconds longer from the same throttle positions. Instead of 4 secs, it is about 5.5 secs. Again, this isn't even WOT, just part throttle which causes a small downshift to aid acceleration. At WOT there is no point in looking at the dash because the whole time it is bouncing from 1k-7k RPM's.

Last call I got was that they are replacing the cluster -- that's it. Not the HUD as well, not the ECU, not verifying any of the engine/trans or ECU/BCM grounding points. But they are waiting for a cluster to ship.

Others have said bad grounds, bad ECU or both was what had been replaced when it finally went away. Really getting tired of being teased by VW TDi owners about having constant loaner cars/trucks and never bringing my own wheels to work. I've damn near driven the entire lineup and every length of Silverado in the past 18 months.

What was the cause of this one? Mine has about the same miles and is now doing the same and headed to George Moore Chevrolet next week for it.