I know the tachs in our cars aren't the greatest, I tested mine out today and spun it to 6400 without touching a rev limiter when I have it set at 6000. That means I've been shortshifting my car the whole time I've had it. What causes the factory tach to be faulty, and can anything be done to remedy it? I'd hate to ruin the interior of a car by adding an aftermarket tach, but that may be the only solution.

 

Bottom line is that they are just not made that well.
Don't have to ruin your interior to mount a good tach. Do the side pillar thing or make a bracket that uses existing holes. I'm sure if you think about it you can come up with a solution.

 

As far as I can tell, my tach is accurate to within about 50 rpm.

It's really just a calibration issue. The tach gets an electronic signal and is calibrated to point to a particular spot for a given input. If you hook up a scanner to your car, you can see the actual value the ECU sees.

400rpm is a lot to be off -- are you sure your limiter is even working?

 

mines 400-500 by the scan tool too, some time my tach sticks too

 

I guess mine is better than most, at idle it reads 1000 instead of 800, and at high rpms it is about 400 off. My friend's is off by about 600 at idle and 2000 at redline (stock 91 305/auto). My rev limiter will engage just past 6400, so it does work.

 

Try this

http://www.thirdgen.org/techboard/el...aayyy-off.html

another one


http://www.thirdgen.org/techboard/el...meter-fix.html

 

Wow, link #2 really breaks it down.

 

My tach is over 2500 too high. I'll have to check those links. Thanks.

 

2500? sounds like you've got a 6 cyl tach reading 8 cylinders, also a tach reads spikes in voltage, so if that tach line runs near a spark plug wire or near a battery cable it's gonna pick up some noise, tach inaccuracy is generally excess noise, in my experience, so yea

check plug wires, and high voltage lines
check and make sure you didnt put an 8 in a 6 cyl car or anything like that and expect it to work
and check yur calibration, if you screwed the thing up and it reads a steady rpm off all the way up, well, then it's probably your gauge face in need of a quick turn, remember the needle moves x amount per revolution, so if it got knocked out of line it'll always be off

hope it helps