Ok, heres the deal I added a thottle body and injectors to the 97 LT1 in doing so I needed to send the PCM out to madz28 to get tuned. well I put the pcm in the car runs great no issues with drivability (actually cured some of my cam surge) but now the Tach progresively increases the RPM shown on the gauge at a faster rate than what the engine is actually doing. in other words when I hit the rev limiter which is set I think at 6700rpms, the tach is completly peged as far past 7000 rpms as possible, completely off the numbers on the gauge? what gives? where does the tach signal come from and why would it change?

 

nobody? how does the Gauge recieve the signal from the Engine?

 

The ECM receives the tach signal from the Ign Module and sends it on to the Tach on your dash.