I have an interesting problem. When I'm driving my car down the road, when I hit the brakes or turn the turn signals on, the tach goes to 0. With the turn signals it bounces up and down as the light flashes. Now, the funny thing is, when it's cool outside, it doesn't do this, but when driving for a bit, or just let the car sit and not drive when it's warm outside, it does this. All of the other gauges are working fine, and when the PCM advances the timing on the car the tach goes to 0 as well, but when I let off the gas and drive normally (not getting on it hard) the tach works fine.

Any ideas on what may be going on? It's done this with underdash wiring from a 91 T/A and currently the dash wiring is from an '87 GTA. I'm thinking that the controller board on the tach is bad possibly. The tach is from the '91 T/A but I have tried a controller from a TBI car and it wouldn't work at all, but I am getting a signal from the PCM for the tach (the LT1 sends the tach signal through the PCM).

Is it possible that the controller board for the tach just doesn't like the signal or could something with the cluster circuit back be causing the problem. I've tried two different cluster housings with the 725 markings, the only one I haven't tried is the one with the 711 marking on it, is there a difference between the two or am I just SOL on the tach and just live with it this way.

Thanks for any help on this.

 

this almost sounds like mine and formularpm's problem with the fuel pump priming when certain lights are turned on...