I have a 1992 RS. The factory tach shows 1800rpm just idling and around 4000rpm at 60mph, and it is in OD.
The original 305 was replaced with a 350 GM crate motor, or at least that is what I was told when I purchased the car. Not sure if something was connected wrong or it is a little more complicatd than that. Any help would be great. Thanks

 

Actually, it's EVEN LESS COMPLICATED that that... not complicated at all.

The tach is bad. They just about ALL are. They all fail that exact way; by reading STUPID high.

There's a post on here somewhere about it... like most such "defects by design"... do a search for something like "tach repair resistor" and see what turns up.

 

The resistor in the tach circuit board is bad

 

https://www.thirdgen.org/forums/elec...meter-fix.html

 

Thanks for all the your help.
It is greatly appreciated.

 

Yah even then the tach is still going to be painfully inacurate. If you have an auto it doesn't really need an aftermarket tachometer. Unless you get a shift kit plus an aftermarket shifter and plan on shifting manually during racing.