Tach not functioning at cold startup

[GSTinCO]

I have read a couple of old posts by people who had the same problem and it never got solved in those threads. So here I go to try and figure the problem.

Problem: When I start the car (1G GSX) after it has sat all night (and no other time) the tachometer does not work at all . It just sits at 0, after driving for 10 to 15 minutes it will start to "wake up" and slowly come back. When I get in the car at lunch (or any other time of day) the tach comes on fine and functions perfectly.

Any ideas / suggestions for fixes. A couple threads indicated the tach signal comes from the coil packs in a 1G but when they switched out coils it didn't seem to help. I am just totally stumped because it doesn't act like an electrical problem or even a gauge cluster problem . Any help would be much appreciated.

 

[Maglin]

I don't know the exact wire for the tach signal but you find it from it's source and see if it's outputting a tach signal with a meter that has RPM functions. IF you have signal then also check for continouty to ground on the tach signal just to see if their is a short somewhere. IF all is good pull your cluster and test the signal at the back of the tach it'self. If it's getting signal and not working then you have a bad tach. It's possible that the coils in the tach are worn and when it's cold they bind up or even short out. Once it warms up they expand just enough to no long short as they move apart and it starts to work again. Give that a try. If you don't have a meter to do this find one or barrow one. Otherwise take it to a dealer and spend the $80 to see what is wrong.

 

[steve]

A couple threads indicated the tach signal comes from the coil packs in a 1G but when they switched out coils it didn't seem to help.

There are two different setups. Original 1990 model cars generate the signal from a module on the coil pack assembly called the tach gate. 1991 and laters cars generate the signal from the power transistor module.

Steve

 

[GSTinCO]

I will try testing the wires and the cluster and report back so someone can find this in the future if it solves the problem. Thanks again guys.