The tach on my 84 15th won't go below about 600-700 RPM's. When you turn off the car it stops right at where the idle was, 600-700. When I revv it and shut it down the needle will go back down but still only to the 600-700 mark.

Is my tach fried or what?

 

It's not uncommon for any tach to sit at an oddball reading while it's not powered.

I'd say you're needle's not calibrated right. But don't take that as gospel yet.

When you turn on the ignition, before you crank the starter, does it go to zero then? It should. If it doesn't then you need to set the needle by using an aftermarket tach. You should be able to run both at the same time.

If you buy one at AutoZone or some other retail chain store, then just take it back when you're done and tell them it didn't fit.

AJ

 

It must be that then because it doesn't go down when the key is turned on.

How do I calibrate it? I'll get another tach like you suggested to use but how do I set my factory tach? Is there a screw in the back or what?

 

You just hook up the "new" tach to the 'Tach' wire under the dist cap. with a wire long enough to go to the passenger compartment. Compare it to what your stock tach says. You know, rev it up man!! If it's fairly close (100-200 RPM) then I wouldn't worry about it. GM tach's are always a little off, as well as a little slow to catch up to 'actual' engine speed. PLUS....You could just have a weird tach.

If it's off a lot, then all ya gotta do is tear apart the dash, slip the needle off the gauge cluster, set it to whatever the "new" tach says that your engine's idling at, and you're done. The needle just slips on and off the little motor behind the gauge.

I honestly think you just have a weird tach. 600-700 RPM at idle is right about where it should idle. Just because it's not going to zero doesn't mean it's bad, or outta wack. I've just never paid that much attention to mine to know if it goes to zero either. But I'm sure I'll pay attention the next time I drive it..... THANKS TO YOU!!!

LOL....

AJ

 

JUST tap on the plastic it will go down, just like in the movies.