Tach goes crazy on my 82 sc

[The phoenix]

Hi all

My tach goes a little crazy.
On idle It goes to 5000 rpm, 6000 then goes back to 1000 and julps again to high levels.
Of course engine remains low rpm.
It happens mostly when i start the car, after i drive it it goes away.

Thanks for your help

[c0metdot]

Ive heard of a tach. What is a..

[gvhriii6602]

When the tach on my 88 started bouncing my oil gage would not hold steady either, in my case the alternator was starting to fail, hope this helps.

[pete3799]

Check your voltage. An overcharging alternator will cause this.

[The phoenix]

Thanks. I'll check that

[911SauCy]

new voltage regulator fixed this issue for me

[ky911sc]

My 83 did this when the Paris Rhone alternator was failing....

[gerakroo]

This problem can also be caused by a defect in your CDI box.

[The phoenix]

Ok. I'll check the regulator first.
Thanks for helping

[gazzerr]

Mine also did this when my alternator went bad.

[Jerry S]

It is a charging or DC storage issue.

As mentioned could be alt belt, alt itself, or when I had this problem, it was a ratty battery.

[armand80sc]

I had similar problem with floating/bouncing tach. It went away after I replaced the ground strap underneath the car. It was in bad shape.

[porsche930dude]

great now i have something to fix. Mine goes crazy sometimes. I thought it was probrobly just a bad connection never thought it could be the vr

[JV911SYDNEY]

Originally Posted by 911SauCy

new voltage regulator fixed this issue for me

yep, my SC was the same

[The phoenix]

I will know in a few days, at the moment the car is at the body shop for a little paint job

[dos531]

Check your grounds.

[porsche930dude]

Well im pretty sure I found my problem. The red wire that goes from the ignition switch to the tach was completely fried. It was spliced before with a connector it must have fried after they did that theres no way they would have left it bare. but it doesnt go all the way to the switch it goes to a connector at the firewall where it goes into a bigger red wire. I cant repair it in that connector im wondering if i can just pull power from somewhere else or splice it to that wire on the other side of the connector. No worries my brother the electrical genious will figure it out