voltage spikes 260z at idle only

[aceofspades]

So I just happen to be checking over the car for summer.

and noticed at idle the voltage was dropping to 0 and spiking now and then to 15-20v at battery at idle! for half a sec then back to about 13.6

but once off idle above 850 it would sit happy at 13.64

so whats the deal?

bad ground? I have no lights or dim issues but some times the amp gauge sits a little on the Neg side

I know the volt-regulator is adjustable but dont wanna play there yet.....

any help before I get silly and take apart a running car?

[30 Ounce]

Check grounds. But it might be time for a new voltage regulator. MSA sells an updated one that plugs right in, couldn't be easier. Not too expensive either.

http://www.thezstore.com/page/TZS/PROD/SEIC03C/12-4082

[aceofspades]

oh that's cheap! yea i have that looks new maybe after market its just zinc...

also what ground besides alt? and why only at idle?

[Wade Nelson]

Remove your battery terminals, clean, and re-install. Ditto for your main ground to the engine block. Do not just "inspect." Remove. Check to make sure your fusible links are all firmly plugged in. tighten them with needlenose (with battery disco) if necessary.

Yo'uve got what's called an "alternator surge" going on. Something is breaking the circuit open, and the alternator responds by zooming the voltage up since the load has disappeared. It's like cresting a hill on a bicycle, all of a sudden you pedal a lot faster with less effort.

Where were you measuring 0 volts? At the alternator output terminal itself? It sounds to me like the same "bad ground" was affecting your meter as the system itself.

[PastorMike]

You noticed the voltage going to zero at the battery. Your engine will not run if you truly have zero volts. And, the validity of the 15-20 volt reading is consequently suspect as being accurate.

What is the voltage between the actual posts of the battery? Hard to believe it can drop to zero one minute, and start the vehicle the next.

Mike

[30 Ounce]

Your ammeter reading below zero at idle leads me to believe your regulator is on its way out. I would do all those things mentioned above but if it still reads blow zero I would change it. The stock voltage regulator is old technology. The one MSA sells is solid state and works very well. I wish I had changed mine a lot sooner than I did because it solved several issues on my car that I didn't even know where because of low voltage. Tach use to do weird stuff, blinkers would slow down and occasionally stop.

[aceofspades]

thanks guys sounds like a plan sadly I got fired today after a good 6 year run go fig =)