I have a MSD universal BTM installed on my 1991 TA 305 HEI system. I get a bouncing tach at idle. It seems to smooth out while driving.

I know it is not a strictly tach failure as when I hook up my Jacob's Pro Street instead of the stock coil, the tach works fine.

If anyone has experienced this please let me know.

Thanks.

 

I think you have to bypass the tach filter, but I'm not too sure.

 

Yes. MSD told me this or you need to buy their part #8910 to fix it.

I have the Jacob's back on-line and it fixes the problem.

Strange how these things work!

Thanks.