ive read some forums and im still not finding anything. i have a 91 vette and the tach is freaking out. with the key off it is all the way down. when you turn it on, it goes to about 7k rpm at idol. when you rev it up it goes well past redline. i just replaced the hei coil pack to see if that was it and no luck. any ideas? easy fix?

 

Tach filter maybe?

 

does the 91 have a tach filter. these are the non digital tach.

 

Well, it could be a couple of things. The tach works off your pickup coil in the distributor through the ignition module. Could be one of those, but more than likely your tach is bad because it interprets a/c voltage readings generated by your pickup coil. My money is on the tach itself.

 

One way to test it is unplug your tach lead from the distributor and use a volt ohm meter that has rpm on it to check engine rpm. Only other way, you would need a scan tool.

 

Get your digidash rebuilt....Cost about 350 at ecklers. I am getting ready to send mine in. Goodluck.