I have a 91 RS with a 305 TBI. Recently got the suspicious feeling that my tach was telling me less than the whole truth, so I hooked up a diagnostic computer and was confirmed that it is reading roughly double. Idle at 650 reads nearly 1300 and 1750 reads about 3200. The gauge always works, never cuts out or gets pegged, just is inaccurate. It used to be right on, but no more. Even if it can't be fixed, I'm having trouble finding a replacement. Someone please help.

 

all factory tach's are off by 400-750 rpm rare they will get that high but i have personally seen it!

 

f_bodyman
if you will do a search on tach fix you will find alot of info. on tach repair.
jdmc
swap350tbi
florida
john

 

Mine did that briefly, you might want to make sure that the dist is properly grounded. Mine was missing that middle ground rod off of the coil. Replaced the coil with a new one, and put that rod in, and it went back to it's semi accurate state.