Tach isn't smooth.

[ryan_george]

I've just replaced my entire instrument cluster with the one from the 325i, in preparation for the engine swap.
Put it in, and the tach/mpg weren't working. So I assumed the SI board. Swapped in the other one from the eta (working 100% fine), and bam! I have action.
Now there is one issue with the tach and mpg gauge. They don't move smoothly. When accelerating they just jerk up/down, but do get to the correct rpm. I tried moving them by hand and I can't feel any abnormal resistance.
Is the tach just about to die?
Also, possibly related, my speedometer isn't reading very accuratly. I haven't had someone pace me yet, but it seems like it's under-reading my speed. Maybe it will fix itself once the engine goes in.

[BavarianBimmer]

Check ground plugs

btw my tach has the same probs never found the issue

[325Projectz]

That SI board might be bad also, try to solder some new batteries to it.

[Jand3rson]

That SI board might be bad also, try to solder some new batteries to it.

Don't some SI boards have batteries that you can just pop in and pop out?

[ryan_george]

My SI board was working absolutly fine with the other instrument cluster. Also, I noticed that the batteries on that board were short, 3v batteries. I thought they would have been standard AA 1.2v.

[BavarianBimmer]

My SI board was working absolutly fine with the other instrument cluster. Also, I noticed that the batteries on that board were short, 3v batteries. I thought they would have been standard AA 1.2v.

EM and LM model style they changed in 1986 I tought

1.2v are the reds and the small were Sanyo in 1986 and up