hey everyone, 1995 sc400 with the 1uz nonvvti. i had a dead alternator a few weeks ago, so i replaced it with an ultima “oreileys” brand alternator. 230 dollars later, the alternator is overcharging after 45 minutes of driving. i checked all grounds. added grounds to intake manifold, and valve covers, new battery terminals, alternator plug is making good contact, and the stud is nice and tight. i CAN NOT figure out why this is overcharging, causing the battery light to come on. so i warrantied the alternator since they have a lifetime warranty, and put the new ultima brand alternator in hoping this was the issue. well it’s doing the same thing. cars at 13.7-14 volts at first, and after about 45 minutes of driving, the voltage spikes to 16.1 volts, stereo shuts off, and then 10-15 seconds later, it jumps back down to 14ish volts. it HAS to be the voltage regulator giving me issues, but i’ve tried 2 new manufactured alternators, and are the chances they’re both bad out of the box really a possibility?
i know oem is always best, but i assumed an alternator was an alternator… so now im frustrated and have parked the car until i can find a reason. i even replaced the plug that plugs into the alternator, to make certain it was getting a good connection. my ecu was repaired for another reason a month ago, and now im curious if maybe the ecu is giving me issues. all i can narrow it down to is the voltage regulator or the ecu?
any help is appreciated, this is my first post, please forgive me if this is not in the correct spot on the forum. thanks

pic of my car, just cuz

 

What voltage is it putting out? I have learned to only buy parts from Autozone and O’Reilly when the situation is desperate. And i always make them test Alternators and batteries before buying them. To often they have problems and it’s nice to catch them before installing it. I would recommend returning that Alternator and try to get your core back. Get a remanufactured Denso unit online. If you had a problem with it not charging then it could be a wiring issue, but an over charging issue is caused by a bad voltage regulator, and that’s inside the Alternator.

 

so it’s running between 13.2-14 regularly, and then once it gets warm, but only after 50 or so highway miles (30mins ish) it will start to spike. i saw as high as 16.1 today for a good 15 seconds. and that’s when my stereo cut out, and the battery light came on, and then when the voltage dropped back down, the light went away and all was fine. this is why i believe even this 2nd remanufactured alternator is also bad. i believe its the voltage regulator possibly? i had a truck that did this too, and had to convert to external voltage regulator because the internal one was junk. i’m hoping its just a quality issue with remanufactured, but im about to get my money back and go get a denso oem unit. the only issue is they’re discontinued.
not really sure where to go from here. everything seems like it’s pointing to the 2nd alternator out of the box. the first one was doing this as well: that’s the only reason maybe i’ve missed something that’s not the alternator, but i was told the ecu doesn’t control charging, so it’s got to be the regulator for voltage i’d think.???

 

I guess I should have looked at your post a little longer before asking what the voltage was doing. Do you have a volt meter in the dash? Or are you putting a meter on the battery when you see the light come on? The problem with O’Reilly, and pretty much all corporations is their shameless devotion to the bottom line. Their parts are all Chinese, they use generic components to build or rebuild everything, and they cut every possible corner just to increase profits by a penny. Their top of the line products like the “Ultima’s aren’t any better than their cheapest option, the only difference is the Lifetime Warranty. I really miss the days when the owner of a store would actually work their and would care about his customers and not just the stock price…

 

I dealt with the exact same problem a few months back on my 94 SC4, but mine was fixed a little easier. I wish I had an exact answer, but my two main “food for thought” questions would be:

How many amps does this new alternator produce?
I know it shouldn’t make a difference, but it’s hard to say with older vehicles.

Did you replace the battery as well?
When my VR was on the fritz, it killed my battery for good. If your battery has already been degraded, I wouldn’t be surprised if it was part of the problem.

To fix my issues, I ended up just getting a new alternator entirely since the VR itself would have been about the same price. That, and the cheapest battery I could find at Walmart, have kept me running strong the last two months. I got my alternator online from RockAuto (BBB Industries N13389). All my buddies have gotten their alternators new there and haven’t had any problems.

Good luck!

 

thank you for the reply! i took the car out for a drive this morning and everything seems fine when I first get in it and start driving. I hit the freeway and after about 30 miles the alternator starts spiking the voltage. I’m confused why it doesn’t do it when it first gets warmed up, but after quite a bit of driving, then it starts to act up. it seems almost like the alternator is getting hot and that’s when the issue starts or maybe the battery is getting hot. The battery tested OK, but it is also two years old. I may try swapping out the battery for my Optima red top that I just put in my Jeep to see if that battery shows any issues. As far as the alternator goes, I think I’m going to return this one to O’Reillys and try and find a better option on rock auto like you said I know voltage regulators going bad is very common with the low quality control parts manufacturers have today, I just found it hard to believe that two alternators in a row were bad out of the box. My aftermarket sound system is probably 10 years old as well. so i’m gonna try disconnecting the system and see if it still does it.

 

This is typical for "auto parts store" alternators. Toyota or Lexus dealer might have this part.
https://parts.longolexus.com/oem-par...r-270605023084