Hi everyone I figured it's time to ask for help on here before I start ripping my hair out lol. I have a 01 ls430 UL that Ive had for over 10 years with no real problems till recently. I bought the car with 60k miles and it now has 140k. It has airruner bags and airlift management and sound stuff, and my OEM alternator was surprisingly enought to keep all that stuff fed for many years with no problem. But maybe 2 years back I kept going thru batteries so I changed my alternator, but I skimped and bought a crappy AutoZone one that lasted almost a year and a half. I also have a radar detector which has a voltage meter so I started to monitor my battery voltage. With the AutoZone alternator, it would read low 13 at idle, but would randomly drop voltage a lot, didn't matter what accessories were on or off. I'd see low 12s sometimes when driving so figured I might as well buy a nice upgraded one this time.

​​​​​ I bought a new JS 240 amp alternator and finally got around to installing it a few days ago. Bought a shorter length belt like they recommended. I also did the big 3 upgrade at the same time. Also swapped in a 3 month old yellow top from my other car which reads 12.7 with car off.

After installing the new alternator, started it up and would read 14 at idle in park. But for some strange reason, as soon as I put the car in drive I see voltage starting to drop to low 12s, and she starts to feel like she wants to die out. If I have all accessories on (lights, radio, two compressors, ac, etc) she hovers around low 13 if I'm not in gear but if I put it in neutral and rev it or just start driving it will go right back up to 13.9...it just seems to dip low when it's in gear at a stop.

Now I'm not sure if this has anything to do with my issues, but I also seemed to develop hard jerky downshifts and it feels like a loss of power the same time as I started having alternator troubles. I also intermittently have had problems with the car accelerating on its own. When it does do that, I put it in neutral and shut the car off, and disconnect the battery and it'll stop doing that for awhile. But it always comes back randomly. My trans fluid levels are all good and am starting to think it's not a mechanical issue, but ecu instead. After doing some reading on here, it seems some people with the same hard downshifts have sent out their ecu or TCM to get fixed by companies like SIA electronics, but they never seem to update their threads on if it really helped or not. I also had some small intermittent electrical Gremlins since my alternator woes, like tilt steering not working, radar control not working, driver window not rolling up or down sometimes.

The only codes my car has thrown since all my troubles started are p0440, found a crack in the hose and fixed that, but I still get that damn evap code and I just bought a new gascap hoping its not the vacuum canister lol.

Does anyone have any advice on where to start from here, or if my just trans issues might be related to my charging issues somehow? Is there a way to verify ecu/TCM issues? I hate to throw money away on the wrong thing at this point. Sorry for the long read, and thank you guys in advance for any help you can give.

 

Before you start pulling your hair out, I would replace the battery. It could have a minor defect that causes higher internal resistance that the vehicles electrical system isn't happy with. I would try a new standard flooded acid battery and see if it helps. Your symptoms are consistent with a failing battery. Also check all the connections in the "big 3" for loose crimps/solder joints and make sure the hardware is clean and tight. The electrical systems in these cars are very sensitive and they usually start having issues like you describe before the battery actually quits.
The battery in a car has two jobs; store energy for starting, and to act as an electrical filter or buffer. It takes the power from the alternator, which is "dirty" with micro voltage and amperage spikes and smooths it out to provide "clean" stable power. This is why everything is wired off the battery and not the alternator.

 

For what is worth, did have some electrical issues recently myself (various systems, lighting, engine not starting immediately, and etc.) and replaced the old battery with a standard lead acid size 24F car battery (10.3 inches long by 6.8 inches wide and 8.9 inches high) 752 CCA at 0° F and 890 CA at 32° F with a reserve capacity of 120 minutes at a cost of $102 and no longer have those issues. But, did not have your transmission symptoms. I tried the battery since it was the first item on inputs (and mainly because it was in the car when I bought it two years ago and was likely not new then) after watching How to Diagnose your ECU - Parts 1 and 2 at How to Diagnose your ECU and Bad Engine Control Module Symptoms And How To Diagnose Your Engine Control Module!
at: https://www.youtube.com/playlist?lis...g_wVVP0jfu4uc_
and:

 

I had a fairly new interstate battery that i believe is still good, reads 12.6 resting with my voltmeter, but still swapped in a 3 month old yellowtop which also reads good, when I swapped alternators. I made sure it was charged fully for the new alternator. I know the new optimas are not as good as they used to be tho. I swapped batteries again today just to see, and still have the same problem. Put the yellow top in my cobra, and have no issues with it in that car.

I crimped and soldered the 1/0 cable I used and heat shrank it. The factory cable I removed from the alternator was in really bad shape,it was really brittle and there was a good 2 inches of copper exposed by the lug going to the alternator.

I also unhooked all of the aftermarket stuff like stereo and air suspension stuff today and still have the same problem.

I appreciate the advice, thanks again.

 

Thank you for the videos, gonna watch them now!