The tach filter, which is essentially a capacitor, only takes out electrical noises and smooths out the tach pulses. I don't think it will make your reading high all the time. But I'm not a wire biter, so electricians may know.
I believe you will need a 200-220K ohm resistor (super cheap just about anywhere). Based on some of the tach issues I've read about with Malibu and Montes. Cutlass doesn't use a filter or all these fancy resistor thingies. They have a little V6 and V8 "plug" that usually loosens and falls out at some point. The later Olds tachs got fixed with a soldered bridge wire, which was the street fix everyone was doing to the earlier ones anyway.
Anyway, these threads may help you figure some things out. Don't know what could be your problem, but good info here.
i tested a good unmolested stock tach and at 3,000 rpm it was off by 250-300 revolutions. at the same speed & doing the mod below tach was now off by 80-100 revolutions. at idle you cannot tell much of a difference, but u will start to notice it as the rpm increases. not 100% accur...
www.montecarloss.com
Below is the original post, but I'm hoping this will be a thread to help correct an erratic/inaccurate/unresponsive tach. From everything I've read it's a resistance value on a resistor 'pack' on the board for the tach that goes out of spec (small, white ceramic piece that looks like an IC...
Electronics - 90-92 Tachometer fix.... - As many of you guys know... barely anyone has a 90-92 gauge cluster with a tachometer that reads properly. They almost always read too high. There has been a multitude of posts regarding finding a solution or a fix for this, but to my knowledge, no...
www.thirdgen.org
But- If you find you want/need a new tach filter...
www.dixierestorationdepot.com
