Tach problems.

[Vettefan87]

I had a problem with my 87 running really rough, so I replaced the the plugs, wires, cap coil etc with all MSD stuff, and ACdelco plugs. Well after the replacement I noticed my tach would only read up to 3 thousand RPM's then immediately drop down to 0, then read again then the RPM's came back below 3 thousand. Could this be a problem with a the tach filter?

 

[vetteoz]

Loose wire on the tacho signal cable off the dist maybe?

 

[Vettefan87]

I just don't understand how it reads fine until 3000 RPM's then drops to zero, then will register the RPM's when they fall bellow 3000.