Calibrating a factory tac
 

Is it possible to calibrate a factory tac? Mine is sitting at -200 when the truck is off.
Thanks

Where does it sit when the ign is on but eng. not started?
It should be at zero then.

If it still needs "tweeking" there is a small hole in the back of the tach(it may be covered with some type of sticker).

Peel that off.You'll see where you can adjust it there.

It sits at -200 when ign is on but not started.

Try adjusting it as descibed while eng is running.

If you have access to an external tach,test tach or the like,hook that up and use that as well.

You can compare the external tach readings with the indash one and see if they are close to each other.

Here's a pic I found on this board.The hole at the top of the gauge is where you would adjust it.
http://67-72chevytrucks.com/vboard/a...&postid=703753