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71 Formula Stock Tach not working with MSD Grid

We've been trying to get my tach working with an MSD Grid. Without MSD Tach adapter, it doesn't work at all. With the Tach adapter, it reads way low. Like about 5 or 600 rpms when it's really at 1000. And it becomes off by more as the rpms go up. Anyone ever run into this? I'm trying to retain the factory tach for a stock look. Thanks

Could it be that the tach is just bad? Is there any way to test? Or is there a place I can send it to?

Quote:

Originally Posted by Dave M (Post 6426986)

The dyno shop had the same issue with their equipment trying to read the tach signal off the MSD model 8563 billet distributer on my engine. Found out we were 500 RPM low which led to big correction on the calculated power. I even saw the same thing with some a portable meter at a Trans Am series event at COTA last year on a TA series car with MSD ignition boxes. The signal wasn't clean enough to get a steady tach reading.

If the tach is reading at all then its likely not bad.

It reads low when using the MSD tach adapter. Didn’t work at all without that.

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