Tachometer reading is off! - BMW Forum

bimmerguy82 · 12-28-2006, 03:32 PM

Ever since I replaced my instrument cluster because of a faulty temp gauge, my tach has been off. I first noticed this while driving on the highway, cause while in 4th gear (auto) at 70mph my tach was almost exactly 3k rpm.
Now I run about 4200 rpm at 70 mph. Also I went and had my car dynoed about 3 weeks ago and the computer was reading a 1500 rpm difference than my tach. anyone know what could have caused this? how to fix it?

BMWJNKY · 12-28-2006, 06:30 PM

Did you put a used cluster in your car?

97alpineM3 · 12-28-2006, 08:52 PM

Sounds like a bad tach bro.... if you have the old one... put it back in... see if it works correctly for a day... if so... then you have a bad part.

Good Luck,

Les

bimmerguy82 · 12-29-2006, 12:39 AM

Yes, it is a used tach, and no, i threw the original one out; because of the bad temp gauge. the thing is, i ordered another used cluster online and it did the same. so, i did not know if it was a coincidence or what. is there some other sender unit that the tach reads off of?

BMWJNKY · 12-29-2006, 11:03 AM

Tach gets its signal from the DME. The cluster could be incorrectly coded for you car. If your DME # is different than the one the cluster was originally coded for it could possibly be causing the problem. If you have tried 2 clusters and they had the exact same problem you may have to get a new cluster and get it properly coded to your car.

bimmerguy82 · 12-29-2006, 10:11 PM

thanks bmwjnky, i will look into that.