Another bad alternator? Or something else?

2007, 5.7L, 210,000miles, 4x4

Some history: My alternator died on a long road trip this past March (3 months ago). It started with a bouncing voltage needle and ended with me coasting into my mechanics shop on only battery power, all electronics dead. He put in a new alternator, started it up to realize he had put in a bad unit, and immediately put in another new alternator. I think he gets his parts from AutoZone or Advance. He passes their warranty on to me. In the process, he somehow blew the main fuse and replaced that. He also replaced the positive battery connection because it was corroding away.

Worked great for the past 3 months, the only issue I've had is a very tiny jump in the needle and some flickering interior LED lights. Checked the battery terminals to find some corrosion. Cleaned them up and all was good.

Fast forward to this weekend, we head out of town and halfway into the 3-hour drive my voltage meter starts jumping around again, the battery light comes on briefly every now and then, and the whole gauge cluster resets for a second. Deja vu. I pull off to the nearest AutoZone and have them test the battery and alternator. Both check out. I buy a Duralast alternator they had in stock to keep with me for the rest of the weekend for peace of mind. Also bought a new negative battery connection thinking that may be it.

Once we got to our destination I cleaned up the battery terminals well, swapped on the new negative terminal, pulled the connector off the alternator, and cleaned up the positive connection at the alternator side as well. I continued to have symptoms for the rest of the weekend but I got around town without issue.

Today we took the 3-hour drive home and had major issues. I was worried we weren't going to make it. See the video of typical behavior here: https://www.youtube.com/shorts/PLUL7T3S67U It would run fine for 15 minutes with the needle steady then jump around for 5 minutes, then back to good.

The only thing I can correlate with the issue is driving through a major rainstorm at the start of the drive on Friday.

My plan now is to buy a new (remanned) Denso alternator and swap it in over the next few days. Just wanted to make sure there was nothing else I should be checking first. I was also thinking about attempting the "Big 3/4" upgrade but not sure if that's related. I'm 99% sure it's the voltage regulator going out (again).

Also, any reason not to go with the max amperage available? Rock auto carries 100/130/150 (edit: 150A it is).

Battery is from 2020 and never gives me any issues starting.

 

Looks like 150A for me. Handy notes found in another thread:

 

Hate electrical gremlins.

I stick to OEM alternators, voltage regulators, starters, AC compressors etc, just because of the electrical issue potential.

That being said, I’ve never had an issue with autozone parts in general with any of my previous hoopties.

It definitely is showing symptoms of voltage regulator issues. However, anytime I’ve had regulator issues it was more of an instant death thing as opposed to a drawn out slow deal.

Id do what you’re doing. Stick an OEM unit in there.

Id really give a hard look at the power/ground cables and the different ground points. Exposed wire, loose/dirty connections (not just to the battery but grounds to the frame/firewall etc) would be just as capable of causing your issues as the regulator.

The fact the wrench popped a big fuse would kind of chap my ass, it makes me wonder if that opened up a box we want closed haha

Sorry not much help, these types of things unfortunately are trial and error.

 

Ordered a Denso reman 150A off rockauto for $285. The local Toyota parts desk had a reman OEM for $400. They would arrive at the same time. I've always had good luck with Denso so that's the way I went.

I spent a few hours removing the old alternator this afternoon. To help myself and anyone that may do it in the future here were my steps.

1. Jack the front passenger side up, remove the tire, and remove the mudguard.
2. Use a big socket to de-tension the belt and remove the belt from the alternator and power steering pully
3. Remove two bolts from the power steering pully. Facing the engine they are at approx 12 and 3 o'clock. One short, one long. Long one goes up top, short at 3 o'clock. There are two other bolts that look like you may need to take them out but you don't. The PS pump was wedged in good and I thought I was missing a bolt, but wiggling it around popped it up.
4. Remove the electrical connector to the PS pump, it will be in the way later
5. Unplug the alternator and remove the positive cable. Don't lose the rubber booties.
6. Remove the metal bracket from the frame that's holding on some wiring looms. Not sure what exactly it is but it got in the way of the alternator removal. The bolt is on the inside of the frame rail.
7. Remove 3 bolts from the alternator and one nut on a stud. I needed my long extensions and a swivel socket.
8. Work the alternator loose and remove the stud, to make more room to maneuver.
9. Pull the PS pulley up and out of the way then remove the alternator over the frame through the wheel well. Easier said than done, took me about 15 minutes to figure out how to orient it right. Careful not to damage the plastic electrical connector on the PS pump

When I had this job done a few months ago I was quoted ~$800. $400 for parts, and 4-5 hours of labor. This is a fair estimate but so far nothing has been difficult. I used nothing but my standard socket set, extensions, and swivel bit. I didn't have the luxury of time last time it went out, I needed my truck the next day for work. This time I have a car I can borrow.

I'll update on Tuesday when I receive the new part.


I also noticed when examining the removed alternator that it was a 100A version. I'm wondering if this had to do with its early failure.

 

Good call, the reman OEM from the dealer would have very likely been a Denso anyways. Best of luck!

 

Finished the job last night. The total time between the two days was probably close to 6 hours.

Steps for reinstalling:

1. Put the new alt in through the frame rail. This was easier than taking the old one out, but still tricky to find the correct orientation.
2. Bolt up the alternator. Install the stud, nut, and 3 bolts. The bottom two bolts are tricky because the frame rail is right in the way. The bolt on the bottom towards the front of the vehicle gets a bolt sleeve, don't forget this.
3. Reinstall the PS pump. Getting the two bolts started in the PS pump took the longest time, you have to get it lined up just right to let the bolt tread in the back hole.
4. Reattach wires and boots, be careful not to get them twisted. I had to undo them all and reroute them because I got them knotted around themselves
5. Reattach the brackets for wiring on the alternator and on the frame rail.
6. Reinstall the belt. Look up the routing diagram, it is possible to install it 2 different ways. It will work both ways but only one is correct.
7. Install splash guard in wheel well
8. Install tire
9. Connect battery
10. Start the truck and cross your fingers that you didn't get a dud alternator (alternatively go go autzone and get it tested before installing).

Test drove it to work this morning ~30 minutes of highway driving. It performed fine, the needle didn't move at all. I am still planning on checking resistance in the big 3 wires, but no immediate plans to upgrade unless needed.

This job was not hard, but a pain in the ass—lots of fiddling around in tight spaces and lots of bolt alignment issues. But, there's nothing that can't be done by the at-home mechanic with a basic tool set.

 

The reason he fried the main fuse was probably failing to disconnect the battery.... I did the same on a Camry, asked my friend to disconnect the battery and didn't hear me and didn't, I failed to double check and my screwdriver slipped and made contact with the alternator.... Quickly fried that fuse...

 

Great write up! Will refer to this when mine goes out. Thanks!