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This is the first time that I have posted a question. I have a 71 Nova SS with a 396 4 speed. Here goes my question. My nova originally had an hei distributor in it. I had problems getting the dash cluster tach working. I was told to put a tach adaptor in, and that didn’t work. I found that I needed to jump the tach wire to get it working. I left the tach adaptor hooked up, because things were working. I was having problems with the distributor, so I went to a regular distributor with an external msd blaster coil. It made a big difference to how the car runs now. My problem is that I took the tach wire that was hooked into tach on the hei, and hooked it to the negative of the coil. The tach now bounces up and down. It’s fine when I am idling, and it works as I am stepping on the gas, but it gets to a point where it just bounces up and down. Like it is losing the current. Any suggestions.
 

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Mike - 74 Nova Baltimore, MD
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A long time ago, I had the same type of bouncy tach needle... but with an aftermarket tach. It turned out to be a bad tach ground wire connection. I redid the ground wire connection and all was well. It's also a good idea to check all of your other tach wires for a good connection.

I also read that the tach needle/RPM indicator will start to bounce if you have bad a spark plug(s)... or bad spark plug wire(s) that are not firing correctly.
 

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Discussion Starter #3
Thanks...ill redo the ground from the distributor and see how that works. The ground is currently hooked to a valve cover bolt, so maybe that isn’t good enough.
 

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Bouncing Tach

On HEI system look at the 1st inn the firing order and the last those are the one to make the tach jump If a chevy motor it would be # 1 & 2 cylinder
 
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