S&W Tach assistance---hopefully?

[427 S/O]

My S&W has always acted up, RPM's jump around and read much more than actual for about thirty minutes before finally settling down to normal.

Any of you had this problem and found a fix?. It runs through a MSD and it's hooked up correctly, the cylinder selection on back is set correctly as well.

[727pilot@usa.co]

You are getting stray "hash" into the line and that is what is causing the problem.

MSD addresses this in their instructions. You should be able to get a copy from their web site.

Quick and dirty try this; twist the wires that supply the tach from the ignition box. Look at your grounding. Make sure the ignition box is well grounded TO THE ENGINE. Make sure the engine ground strap to the frame is in good condition.

[427 S/O]

Ground!, someone else suggested that and everything checked out. I might, as a test, run a ground from the tech directly to the - battery. Thanks.

[nevermind65]

I had something similar happen to me before. It ended up being a bad alternator. The alternator was charging just fine and the volt meter showed nothing erratic. I bought a chrome alternator by chance and the problem went away. I gave the old alternator to a friend, he put it on his car, and called telling me his tach was going nuts. He bought a new alternator and again, the problem was gone.

Not sure what the deal was, but it was creating some type of feedback through the tach.