Hi Folks,

A friend owns a 87 GTA with factory digital dash. The tach is acting strange. Reading is completely inaccurate. In idle it shows about 4500 rpm and when you hit the throttle it pegs out completely. How is that possible? My understanding is that the tach gets the signal straight from the ignition coil. Coil is new, didn't change the reading. Is the tach bad? Car also has the "old style" tach that was used in late 86 cars for MY 87 i think. Not the "half round" tach that was used in 88. Are they different? Fuel gauge also always reads full but someone messed around with the pump wiring pretty bad, wired it directly to ignition switch without a relay or ECM in the circuit, it runs all the time from ignition on and never stops. Also DIC shows several errors but thats another story. Anyone have any idea whats going on with the tach?

Thanks!

 

I've got an '88 with that later-style tach, but it has a similar issue.

Most of the time it works fine. But once in a while as I'm driving, the tach reading will climb progressively up the scale. The idle will be at the normal level when I start, but eventually idle will be at 1500, 2000, 2500, and up. That becomes like the new base (idle level) for the tach. It will climb when you rev the engine, but drop down to the new higher level when you're not revving. Eventually it lights up the entire tachometer.

Park the car, next ride it's back to normal.

Doesn't bother me much since tachs are pretty much just for show on an automatic car. The rest of the digital dash works fine.