So recently when I've been driving spiritedly (pedal at WOT) soon as I hit boost, around 3500 RPMs the tach just falls flat on it's face and becomes unresponsive! The speedo is fine, and my blinking CEL shift light still works. Any idea what would cause this? I tried reseating the cluster wires.. I tried reseating the distributor wires and I checked ALL the grounds.

 

Check all the grounds
maybe there is a bad ground

 

All the grounds are solid

 

Ive heard of failing ignition coils giving bad tach readings.

When this happened to me the tach would cut out intermittently, ended up being a broken wire at the dizzy that didn't look broken to the naked eye.

 

Have you monitored/compared system voltage before and after gauges fail?

 

What year/model chassis do you have and what ECU are you using ?