tach stops working while driving

[Shudson105]

I have a 93 Formula and when I drive for more then 20 minutes, something happens (perhaps temperature related?) that causes my tach to spontaneously drop to zero and the car will slowly stall out and backfire. The car can be immediately started up again and driven till the problem happens again. All gauges read and work fine while the tach rests at zero...the engine still runs too, although you can tell it's slowing down. The throttle is unresponsive at this point.

I recently performed a complete tuneup (GMPP optispark, MSD cap, MSD coil, GM plug wires, NGK plugs, and new waterpump) and this problem has happened before and after the tuneup. I noticed my optispark connector was corroded (green crap everywhere) and I tried cleaning and scrubbing it, but have not replaced it.

Any thoughts?
Steve

[bigrondownhiller]

Could be a lot of things. First I would check the battery connections for corrosion. Next would be to have it scanned while driving to see what is going on.

[Shudson105]

I did check and clean my battery connections which had no effect. No codes were thrown when the problem occurred the first or subsequent times. The scan also shows my tach signal dropping to zero while car is running while the vss shows my car slowing down. Engine still running and in closed loop state when this occurs.

[bamaz28]

i would think battery concections also, mine + was lose took me forever to figure it out. i would drive down the road everything worked fine then all the sudden tac stopped working, mph was go up and down all the lights would flash on and off then it would quit like nothing ever happened.