I am wonder ing because at WOT my tac moves up and down at around 4500 by a couple 100rpm. Do I have ingnition problems at high rpm or is it just a crappy tac.
thanx

 

For the most part, very inaccurate. And almost always not accurate enough to set anything on the car by.

 

agreement. Installing an autometer tach in my car made me realize how much the stock tach bounces and just generally shows you incorrect stuff. heh. at 80 MPH my stock tach says 2200 RPMS, but the autometer says 2000 RPMS. this just gives you an idea of how incorrect these things are. my other car's factory tach is off by a factor of 2 cylinders, that is every 1000 rpms it sees an extra 200 rpms. weird crap. and no, its not a 6-cylinder tach on a v-8 engine. ripped it out a week ago and replaced with autometer... what a difference! im not shifting at 8000 rpms anymore! yay!