Owner since 2006 160,000 miles.
Have read some other postings about alternator problems but this is unique.. Been fixing cars 60 + years except for tranny work so pretty up on systems. New alternator replaced last fall due to power steering oil contamination in armature.

Storyline: Grandson call needing jump, bad battery after driving the morning. Calls back got a jump, car at home. I check it out, have to jump off. Check the battery warning light, not illuminated. Volt check 12.5 while running. Lights on 12.3. AC on 10.4 flat line. Order replacement because it is warrantied. Pick up next day, ask them to bench test old one. TEST IS GOOD. Okay will install old once again BUT stop by O'Rielly's for a second test. TEST IS GOOD. Install old one, again 12.5 on meter but will increase to 12.9 when increase idle. BUT with AC on, drops to 10.4 again even with increase idle. Pull off and Monday take it to my Starter & Alternator rebuild shop. He pulls it open, said everything id okay and TEST IS GOOD. To check a couple of connectors before installing. All reading were normal. Install, same problem. Take it to Advance load check while on car. Checks same results, 12.5 idle, 10.4 AC running. Got the new replacement alternator to install, it load tested good before I left the shop. NO CHARGING after install. Installed 1 month old battery, still no charge.

TEST done: 10A ALT fuse under hood & 7.5 meter fuse in fuse panel test good.
12V to battery cable connecting to ALT. [ 12V to connector from 10a fuse. ] [ Second connector; Zero V with ign off ~~ 12V ign on.]
Checked output terminal while running 12.5V Grounded to Alt body, to engine, and neg. batt post all same readings.

Sorry so long. Wanted to show everything I have been told to do and past experience has been tried. Charging schematic from my.alldata/.com/repair. If there are others in the loop, I am not aware of any. Suggested might be ECM but schematic does not show other pages. I hate to start buying parts no fixing the problem. Infinity wants my to drive it there. 60 miles ~~~ NO WAY.

Any suggestions to add what I have not tried will be greatly appreciated. Thank you, Thomas

1)There is no ECM intervention in the charge system, the dealer is NOT the answer, you are
2)The alt belt is skinny and overworked, how is the fan clutch? Locked will mess with you.
3) About me...someone that has done/currently doing drivibility/general repair for 35 years, actively endurance races a J30 (now J45) for the last 11 years and has owned (8?) j30... I can tell you the alt belt has to be new and tighter then you would ever imagine (guitar string tight)or the j30 will not charge properly and can behave as you describe(silent slipping is possible when the belt grooves get deep). While unnerving, the way over tight belt has never killed any bearings, never hurt the water pump or snapped in the 28,000 miles of balls to the wall road racing with the VG30de

With it running on a lift, use your old school trick with a screwdriver to see if its making magnetism, if it is, suspect bad belt (you have a bad belt)

Saying that

Barely have messed with 96 or 97 (less HP) but the alt is the same part from 93 to 97

Currently have one parts car doing exactly the same as you, got the car for $50 less because it wouldn't run without battery but while trailering it home left it idle 2 hrs with the 4 ways on, never killed the batt, the belt did squall then quiet, problem got worse when tightened belt, have not looked at it again to confirm.

The best units I have raced with were 1000,000+ mile used factory units carefully cleaned with brake clean and blown out, non oem replacement regulators in autozone/advanved/peppboys units are crap, Orileys near me has decent alts. but never bought one for a J30

Thank you for your response. I made mention this afternoon to my Alt rebuild shop owner that I had 83 looks but no replies. And probably because of my full description of problem and steps already tried to fix it. Then just checking, I see a reply and suggestions from you that I have not given much weight to cause.

So, thank you up front for your input.

Last fall when I replaced the Alt from PS oil contamination, ( a stupid engineer mistake, mounting the Alt bottom of the engine subject to leaking hoses, high water shorting out) I saw the belt was well past its prime, oil soaked, missing sections of ribs, totally in need of replacement. But since I had to pull the PS and AC belts first, decided to put off replacing til another time. That time came on May 27 when I had the car for a day to fix other short ends. Gave car back to grandson on May 29th. One week later; Dead Battery.

I don't have a belt tension tool but just tighten a new belt just enough to keep from squealing and retighten about 500 miles later. Seems to work okay. I used to tighten as you said, (guitar string tight) but one time on a Pontiac Grandville, I did that and the Alt pulley bearing froze and broke the Alt belt. This was in mid Jan while driving from Anchorage to Fairbanks. I made it back home with no heat except for some through the vents with no fan and no lights or other electrical. Cars did not have all the fancy fuel injection or electronic ignition so that got me through. The garage told me too tight caused it and also puts side pressure on the water pump, so from then on I did a just tight enough install.

So tomorrow I will try your suggestions, On surface, they have good merit and appreciate your input.

Looking at the fan clutch, it seems okay with car running but will check it as well as tightening the tension on the belt. I have never done the screwdriver test on a working Alt, in fact never thought about it. I know it is putting out some to get the V to read 12.9 when I increase idle so maybe not enough to cause the screwdriver to get attracted. That test makes me nervous and don't want to see something go wrong and a hole in the radiator or condenser.

What puzzles me is at increased idle V reading is 12.9 but with AC engaged immediately Volts drop to 10.4 with no increase in voltage with increased RPM's or tell tale belt squealing.

Well, with that said, I will close for this session and cross my fingers until morning. Hopefully, ~~~ I can report problem solved thanks to you tomorrow evening. I do have another problem I will address about tire wear another time.

PROBLEM SOLVED = IT WAS THE BELT NOT TIGHT ENOUGH.

THANK YOU - THANK YOU - THANK YOU

THIS SITE IS THE BEST.

Glad I was able to help, not sure what drew me here the other day but honestly, facebook has ruined the place, not to mention, there are fewer and fewer J30 in the wild.

Happy motoring

Well, lets just say that the Infinity gods sent you a message that one of your fellow J30 was in dire, desperate need of your expertise. One more time, I thank you and my grandson thanks you. Thomas