Screwed up stock tach......

[2001SandstoneLS]

Alright, so, my 01 is down at the moment getting a 383 stroker, so in the meanwhile I'm borrowing my brother's 03 Z71 Silverado, and I hopped in it for the first time today, and saw this problem with the tach:

[media]http://www.youtube.com/watch?v=s0tRAn0wMR0[/media]
[media]http://www.youtube.com/watch?v=YkzhZX-3xDw[/media]
[media]http://www.youtube.com/watch?v=fWfbqV-AGas[/media]

Has anyone else had/seen this problem? Thanks a ton.

[tbplus10]

Yep, check the wiring connections first. Back of the gauge pod, under dash at the ECU, outside of the firewall, and at the engine. A loose connector can cause this.
Theres a connector in the engine compartment below the brake master cylinder that goes to a lot of the dash functions, make sure it doesnt have moisture or any fluids in it. If it does use electrical contact cleaner to clean it.
I've seen this connector get brake fluid and water on it and cause lots of havoc.
If the connections are good get a diagnostic testor on the system and see if it has a bug. GM had some intermitant gauge issues that were traced back to a signal relay and wire harness.

[2001SandstoneLS]

I'll have to check it out, thanks a ton!

[moogvo]

The stepper motor that controls that gauge has gone bad. GM apparently had quite a number of instrument clusters where one or more gauges either failed or went just plain nuts. GM wants $400.00+ for this repair, but you can fix it yourself for about $10.00 per gauge by replacing the stepper motor. there's a guy on ebaY selling the replacement stepper motors. I just did my speedo yesterday. It took all of about 5 minutes to get the cluster out, another 10 to disassemble it and replace the motor, and about 5 more to re-install it.

I do have an electronics background, but all that is needed is a small amount of ability with a soldering iron.