Hey everyone,

Had some questions about my charging system before but have put it off and needed some thirdgen advice.

I trust the gauge as I went out and tested voltages and they read near exact what the gauge was reading so I ruled that out

My symptoms are:
Sticks dead at 13 during the day with aftermarket stereo head (no amps), and economy vent air.
With headlights on at night including everything else, at idle, it drops down to almost the warning area, about 9. All lights dim.
Occasionally it goes up to 14 during the day while cruising if I've been driving a while.
Cruising at highway speeds with headlights and all sports 13v

When I bought it over the summer the owner said he replaced the alternator when he replaced the ignition system (which did look all brand new and a new msd ignition module and the alt looks very clean and new).
Knowing the quality of new parts when I worked at auto zone, I wouldnt be surprised if the alternator was fried. And its a pita to test it from my sidepost battery, and occasionally yields false results at the auto store..

Battery is a brand new interstate which fixed a ton of my previous rough idle issue .

So I'm wondering now if it may be a voltage regulator, since I assume he didn't replace it. Any advice on steps to take?

 

It should be around 14.5v while it is running. Anything higher (than 15v) is a bad regulator, anything lower would be the alternators doings. A bad alternator/regulator can damage a battery and iirc a bad battery can affect the alternator so don't let anything go on for very long. For example, whenever you're running less than 12v you're running off of the battery and draining it.

You can bring either in and get them tested but making a cigarette lighter lead for your meter can make things a whole lot easier.

Never trust a stock gauge. It was never accurate to begin with and it's ~30 years old.

 

Voltage regulator is built into the alternator on all of the GM alts/cars since 1973
Before '73 the voltage regulator was external, little black square box mounted on core support or firewall.

So yeah if the alt was changed on yours, so was the voltage regulator.

 

Could the alternator not be spinning enough? The alternator is only run on the crank I believe.

Also I'm sure my gauges aren't perfect but at idle its very obvious that the alternator isn't charging very well. And I haven't measured it at the point with a volt meter but it is very noticeably running pure battery

 

Test voltage in two different places- at the alternator charging post (vs. ground) and at the battery terminals. They should be within a few tenths of a volt of eachother, assuming the battery is near full charge. It should be around 14.5V. If it's not in either location, it's likely the alternator just isn't doing its job.

If the belt is on the alternator, it's spinning enough.

 

Just another thought. I had a similar problem when I bought my 87 iroc. Voltage was fine while driving but really low at idle. Replaced the battery, alternator,etc. Same problem. It turns out, the previous owner had installed under drive pulleys on the engine. This caused the alternator to spin too slow at idle. I put a slightly smaller pulley on the alternator and problem solved. Haven't had a problem since.

 

I will test the voltage at the alternator and battery today at idle to see what I get. Thanks for that!

And I heard about underdrive pullys being an issue for alternators. I'll take a look though

More than likely if the voltage reads low on the alternator test, I will more than likely shell out 50 bucks for a new one. Just would hate to have it kill my battery or worse while I'm far away

 

FWIW, I had a lifetime warranty on a starter that I ended up replacing several times so I found alternatives to get away from that. I've had better luck with junk yard parts and if that doesn't work I have 3-4 local shops that rebuild starters and alternators.

 

Sorry for the late reply, been a busy time moving and have had a lot of car accidents

I've just bought a higher amp alternator on Hawks. Pretty sure they just bought a crap alternator.