vannmike

I recently installed a 4l80e into a 77 corvette with a US shift controller, also installed electronic tach and speedo at the same time. The problem I'm having is my tach is acting up. With the key in the on position, the tach will just slightly bump up and down. It's a consistent flutter. And you can hear it in the speakers..this is with the engine off/key on. The us shift controller is registering this bump as well. Basically it will read 95-100 rpms with key on- engine off.. any thoughts?

this is causing issues with WOT throttle shifts because the controller uses rpms to determine WOT shifts..

kernalclink

I would start with checking your grounds...

mikem350

The noise in the speakers is indicating a problem in the +12V power lines or grounds.

Have you added any other new electronics?

vannmike

yeah. Added them at the same time I did all this. Sub, all the autometer gauges in center dash as well.