Bad alternator problems

[Heen]

Hey all,

Running into some issues with what I think is the alternator on my 71 Z. I got my battery tested to find that it's not the culprit. Before starting the battery voltage is around 12.82 V and when the car is idling the voltage is at 12.11 V. The car idles lower than I'd like (500 rpm) and thats at full choke. Battery is drained a fair amount after running it too. I haven't checked the spark plugs yet, but I think I'm gonna check them once the car cools down, but I'm fairly certain it's the alternator. Is there anything else I should check before ruling it out to be it? The belt on it is tight and the voltage does go up a little (12.35 V) when I give it some gas, but I thought the voltage was supposed to jump up over 12V if the alternator was working. And is it possible that a faulty alternator would cause the car to idle lower (not enough spark?)

Any help/ideas appreciated! ☺️

[jonbill]

Yes it should be at about 14v if the alternator is working.
If the alternator is related to the low idle it might be that the alternator is putting a lot of load on the engine. Try disconnecting the belt and see how hard it is to turn the alternator by hand.

[Heen]

A quick update. I had the car idling and had a buddy take off the positive lead on the battery for a second and put it back on. Immediately after putting the terminal back on, the idle speed started going way higher (started 500rpm at full choke, went up to 1100-1200) before it went back down shortly after. It could be possible that it's the voltage regulator. @jonbill I think I'll give that a try next, thanks!

[Zed Head]

There's a pretty extensive test procedure for the alt and the regulator in the FSM.  They even show how to adjust the regulator.  Old school stuff.

[Heen]

@Zed Head I'll give it a read tonight. I've been neglecting the FSM so much, reminds me of a school textbook ?

If I make any headway I'll post here.

[Patcon]

Be careful about disconnecting an alternator while the engine is running. You can damage components on some vehicles this way

[Heen]

@Patcon Yeah that may have been a risky deal. I think I'll not do that again. 

I looked into it more and I think I may go the route of the 280zx alternator conversion. Seems easy enough and will be a catch all with a lot of the electrical unknowns and probably future proof me as I wanted to hook up some more modern interior electrical bits. I'm going with the kit on zcarstore so I don't need to cut or solder any of the original wiring harness so it'll be able to switch back if someone wants it original. 

Once all the parts arrive and I slap them on I'll report back anything new.