Hi everyone,

I bought my car not running well, found the issue it had and got it running, started driving it around town a little, then one night this happens:

On a spirited shift from 2nd to 3rd my cluster lights go dim and volts drop to like 10 or 12 (just over the 1/4 mark on the gauge). Luckily I was on my way home and just outside my apartment complex. Parked it, started it up the next night and all was good. Drove it for a while and same thing happens but not related to a hard shift.

I notice my volts seems to go up with higher rpms (constant, not revving) and all seems good, but a quick rev and the volts will fall back down to the low point. Now it seems unrelated to engine speed, but relateively quick changes in rpm either bring the volts back up or knock them down.

Here's what I think:

Brushes in the alternator or some other component is worn, failing to make contact sometimes. That or I've got a diode going bad in the voltage regulator.

What I'll likely do:

Get a new alternator. I may get this one tested but it could test good if everything works all right during the test, but I could reinstall it and it still wouldn't work, so a test would kind of be fruitless. I'll also go over other connections I haven't looked at yet for corrosion, etc.

What I'm wondering:

Most alternators I've had go bad do it all at once, so this intermittent thing makes me wonder. Has anyone else had this issue and it turn out to be somehting else, like something out of the ordinary specific to F-bodies? A weak engineering point or inherent design flaw?

I'm pretty good at troubleshooting but the reason I join these boards is to find all the little tricks of whatever car I own so gain some knowledge and save some time.

 

You sure you didn't lose a ground somewhere? I also can't recall having an alternator that worked sometimes and not others. Some fall-off in the voltage from cold to hot is normal, but what you have going on sounds more extreme than that.

Start by getting the alternator tested and go from there is what I would do. If it tests bad, then you know you got it nailed. If not, you still haven't spent a dime.

 

That's what's getting me. The only other time I had something close to an intermittent problem was on my S-10 and a bad production run of replacement alternators from Auto Zone. The weld holding the + stud in would break and make intermermittent contact or none at all.

It's like it's either charging, or not and running off the battery. I'll need to poke around a lot more before pulling and having it tested and/or replaced because I really haven't been able to give the electrical system a good once over. It had a fuel problem when I bought it so I've concentrated mainly on that. Like the fuel problem though (bad hose on the fuel pump) I figured this may have specifically happened to someone else or it's something common in these cars. I can't say enough how awesome it is I was able to get that fuel issue fixed by reading about it on this site. Saved me many many hours and dollars.

 

Check the belt put the battery on trickle overnight. I have a f250 similar issues pulled the alternator had it tested was fine. Next day similar issues swapped alternator and no more issues

 

Hey everyone. It turned out to be the alternator after all. I found one in the junk yard (miraculously; they are usually gone as soon as the car gets there) so I swapped it out, and the belt from the donor was brand new and they gave it to me for free! Woohoo!