What would cause the tach to be jumpy if the car is charging fine?

[The Green GT]

Today I was on my way back from school, stopped in traffic, and looked at my tach and it was jumpy so I looked at my voltometer and it was fine. But I gave it a little gas and it would stay jumpy the whole time. The voltometer was reading between the O and R. And my radio would always go off before the tach got jumpy and it stayed on the whole time. I took my U/D pullies off so thats not the problem. I noticed it would do it when I was stopped and pressed the brake. Then when I let off it would go back to normal.

 

[94Cobra69SS396]

This happened to me when my coil went bad. It first started making the tach jump then a few days later the car started to misfire a little. I replaced the coil and all was good again.

 

[The Green GT]

This happened to me when my coil went bad. It first started making the tach jump then a few days later the car started to misfire a little. I replaced the coil and all was good again.

Damn, maybe Ill go buy a coil and keep it in the trunk just incase.

 

[1TallMF]

I'm thinking the coil too. Check the connection on yours maybe, I know the wires on mine are somewhat loose at the black plug connector, but I haven't had any issues with it yet.

 

[badstang123]

I agree that it could be the coil. It could also be a ground. In MY case, the tach was jumping and the car missing, and it was a bad spark plug wire. I would guess it is one of those three things.