leowin

Hey all, I am having a problem with the 90 vert's tach. When i first start it up it will not move and then about ten or fifteen minutes later it finally starts to register then it seems to read a little to high by maybe around 300 rpm's.
I searched tach problems but i didnt see anything pertaining to this problem. Anyone have any ideas? Thanks

aklim

First thing you can try is to remove the Tach Filter.

https://www.corvettemods.com/C3-C4-C...MaApwrEALw_wcB

https://www.corvetteforum.com/forums...ch-filter.html

If you bypass that, your tach might be a little more bouncy but lets start with that. If it isn't accurate or you don't think it is, that is another issue. One way to confirm is to use an inductive timing light with a tach. The better way is to use a scanner to see what the ECM thinks the rpm is. I do both methods to ensure that what I expect to see from the tach is accurate. It was not so I sent it out for rebuilding eons ago.