I have had trouble with my boost gage/map reading reporting unaccounted air when compared to the MAF reading. It is somehow related to my electrical system. Here'* the story, put in the context of Danthur'* write up on the alternator/battery check (valuable info, that write up) Also, I was getting a p0171 a while back, but that has stopped since I replaced the EGR pipe and reseated the TB. I'm confident this isn't a vacuum leak.

The multimeter is tapped off of the terminals on the battery (meter gage taped to the window)

At dead rest, the battery is reading 12.4v. Sitting for a day or two, it loses only a tenth or two.

Firing the car and driving it around, it pegs around 14.3v. I'd like higher, but its in range and holds steady under throttle. While moving, I start stressing it with window buttons, heater, high beams, brakes. There are drops, but they are instantaneous. But the overall operational reading starts to erode over 15 minutes of this. Down towards 14.0. (If I turn everything off and drive for another 10 minutes, we're back up to 14.3. But i left it impaired for the next paragraph.)

Now, I pull into the driveway,engine running, put the brakes on and leave in gear. The boost gage is idling near -7.5, not -10 where you think it would be. Then I start piling on the accessories, and the meter is showing some really ugly stuff. What I'm reading off of the battery connection keeps fighting to get back over 14, but as i add on accessories, it'* not only briefly just dropping a .5v. Its quick low points are under 13v and the boost gage is fluttering. The more I stress the system with accessories, the higher the boost gage gets.

My first thoughts are a very old and tired, but operable alternator. But I know there is the voltage regulator and rectifier, too.

Any thoughts would be appreciated.

Notes:
Cables and their connections are cleaner than my teeth.
The battery is a few months old, and a top cold cranker. It replaced a battery which for some reason read OK at the test at Rice Central. But I discovered it was the most badly swollen battery I had ever seen. Ever.

I would get the batter rechecked at another place, just to be sure. While reading I was really thinking the alt is getting tired. Also check the serp belt. Does it looked glazed or worn? It might be slipping. But I'm still thinking the alt is going mainly because it starts out good then gets worse as it gets hot. What year is this on again? Check the plug on the alt, how many wires do you have? If you have 2 wires there is a cheap option to try called a alt sens wire. I have a write up on that. https://www.gmforum.com/t278806/ This can get you about .75 volts. If you have 3 wires then you can't do this.

This is on the '98 SSEi. I didn't explain that right. The battery is a few months old, I took the fatty out as soon as I realized what was going on. It was wrapped in a rubber cover. Checking the cables for the 100th time one day, I took off the cover and knew that battery was a drag on the system.

Gatorbacks with less than 6k mi on them.

I have two wires. I know this because I put an 8G wire from the alternator terminal to the relay box connect to complement the long traveling 10G circuit. but that strong point is more for fast powering the battery. It seemed to help a bit. ZZP looked to have something along the lines of what you are doing, but they sent it to me, and there is no way that ever had a chance of fitting. Even though they said it would. "No returns" on electrical stuff. We'll see about that.

So what does that 3rd wire do? Provide a read on the voltage in the circuit?

And I'm starting to lean towards a fresh start with another alternator. (I'm real picky about primary systems. My nirvana would be a solid alternator, with a nice .75 pop ) Over the past 4 years at BC/BF, I have read too many posts where either the battery or alternator was in lousy shape. Somehow the two would work together to fake a passable circuit. And when one was replaced, the other one was on the verge of death, or died shortly thereafter. But i still want to hear any further thinking.

edit: the reason I'm so hopped on this is because I just got the multimeter today. All info prior to this, was just guessing something was going on based on symptoms.

The 3rd wire is a sense wire. I believe it'* 2000+ have this stock, but 96-99 didn't have it. I might be off on those years a bit. It'* a good, cheep fix for low voltage, and the only thing you can do with these years.

The one from ZZP wont work on our years, I already told them that and they said they were going to put that on their site.

I'm still leaning towards your alt going out, but even if you change the alt, the sense wire is a worthwhile mod to have.

Yeah, that makes us a majority of two. I want to know for sure that the electrical source is sound. even if to just eliminate that as part of my quandary. Like bad or corroded cabling in that system can cause a whole host of seemingly unrelated problems, if you are starting off with a weak or stressed alt, you're in the hole to start.

Oh, and that sensor wire is definitely going on.

You are developing a fine library of quick info/tech articles. The charging circuit test one led me to get the multimeter, and do the testing myself, which shows it all under true operating conditions. Thanks for the effort, and keep it up. Younger guys getting started need it. And the senior set like me are getting more involved in caring for their cars to save money and have some fun with it.

These are troubled times for many Americans and things are going to change again. Some I think will be for the good. Our love affair with cars has always been at the heart of the American culture, maybe it will be time to revisit and reacquaint ourselves with that. (stepping down off of soap box )

Every person that saves some money using this site is what makes our efforts worth while. This is your car, and you really should know more about it then where the gas goes. Nothing annoys me more then a person dropping off a car and they don't have the first clue what'* going on. Even a basic understanding is better then some of the people I've met.