1991 tach problem
Racer
Joined: Aug 2005
Posts: 336
Likes: 3
From: State of Confusion
Welcome to the '90 and '91 club, this has bitten a lot of us. I installed an aftermarket coil and that wigged out my tach, it wound up that I had to remove my filter to make it work. I wound up going back to a factory coil and it worked perfectly. Anyway, do a search and you will find much info on this subject.Adam.
Burning Brakes
Joined: Apr 2006
Posts: 805
Likes: 3
From: Okeechobee FL
But I posted some pics of the Tach Filter location in a thread about a month and a half ago, a quick search should find it.
Pro
Joined: Mar 2007
Posts: 526
Likes: 1
From: San Angelo Texas
I chased this down a bit. There are a bunch of resistors on the control board for the tach. If even one of those resistors gets flakey things get crazy. From what I have read the tach filter doesn't usually fix the problem. Mine reads high (not as high as yours) and I am at a recalibrate like the other guy above me. I forget the place, but it was around $175. I would just start saving my $$$ for that. There are aftermarket tach filters that are dirt cheap. I changed it just for arguments sake. Didn't do anything, but at least it's new. 
