I recently noticed that my stock 91 Z's gauges are off. I know from browsing around that you should not expect accurate factory gauges but the tach is WAY off.

This first came to my attention when my wife said something to me about how fast I was driving (I normally limit myself to 5 over the posted speed on local roads). With her pacing me and later using a parked radar gun I verified that I am actually doing 45 when my gauge is showing 40.

Now the tach is another story. It shows me turning 2800 RPM at 70MPH. It also shows the car making the 1-2 shift at 5500 RPM at 2/3 throttle. Over the past 7 years, I have driven this car very little but this year it became my commuter car and I am now discovering these little problems. Last year the ECM started to fail and it was replaced. Could this be the root of the inaccurate gauges?

Any thoughts. Car has a 350, TH700, and 3.42 rear.

Steve