I tried posting a video, but I guess I'm not smart enough yet lol.... So my tach was fine till today.. I started up the car and it dropped below zero at about I guess a -3. it still seems to respond , but when it should be around 6k or 7k it's more around 2-3k.
Please help... I'm new to the 8 and still depend on the tach to know how high to take it before shifting. Thank you.

 

Upload the video to YouTube and post the link here.

 

 

Yah, that's broken.

First time I've seen something like that.

 

That’s a new one for me. Only thing I can think is it’s an electrical problem. Either bad battery connection, bad ground or a wire has shorted.

 

The needle could have somehow rotated on the shaft somehow. Definitely a new one. You might have to open the gauge cluster to fix it.

Or apply stickers to mark the new rev range...

 

Thing is, it was fine . I drove it about 6 miles with no problems and parked it. Started it up an hour later and it does that.... frustrating.
I am very grateful to all of you that took your time to comment. I will post back what I find.

 

Did you find a solution to this? Once, you find anything please post it here.

 

I haven't had time to look into this just yet, but I noticed something odd today.... I hooked up my obd2 scan tool to clear a CEL and it did like it sometimes does and said "failure to connect". However, I noticed that as soon as the screen went from trying to load to saying "failure to connect" that in that instant my tachometer flipped back to zero like it should be , but it then went right back to being pegged way below zero. So what connection is there between the tachometer and the obd2 port/connector if any ?

 

Likely an issue with your computer modules. They are beside the battery box just take the plastic cover off. Try cleaning all those connectors then add a dab of dialectic grease. Powered off car with battery disconnected of course. Allow an hour to dry after cleaning before reinstall. First thing I would try.

 

Did all of the above...no change. I jiggled the obd2 port and wires with car running and nothing happened. However, when I hooked up my scanner and jiggled it, the tachometer needle began to jerk further backwards and the little display strip thing above the radio (not sure exactly how to refer to it) began to blink off an on as well. Anyone have a wiring diagram for the obd2 or know what connects the obd2 port, tachometer and the little display strip thingy ? There must be something ....a ground or something....

 

It's a mystery... is the battery ok? Funky electronics can be a symptom of bad voltages. If that's not it you likely have to replace that gauge cluster.