Non Buick charging issue

[Flyin Brian]

Ok this is not on my GN but on my 1997 Chevy Tahoe.
A few weeks ago I was driving it and the alternator quit charging.
I figured it was the 17 year old Autozone alternator so I took it back and got a new one. They did not even test the old one because the bearings sounded bad when turning it by hand.
I put the new alternator on and fired it up and it worked fine. A few days later I started it and no charging.
I checked voltage at the battery and at the lug on the back of the alternator and only got 12 volts.
So I figure naturally that there must be a problem with the power feed to the alternator.
I replace the alternator pigtail and put in a connector to connect to the factory wire.
It worked fine but a few days later I start it up and no charging. I disconnect the factory feed wire and figure it is not supplying power due to the whole going through the light on the dash thing but it shows 12 volts. So I assume the alternator has a problem and take it back to Autozone and it checks out fine.
So I put it back on and run an additional hot wire to the other terminal "I" I think because you can do that with the Delco 130D alternator.
Now I have 2 hot wires going to the alternator and I check all the battery cables and grounds and everything is fine.
It works for a few days but again I go to start it one morning and no charging.
I figure the battery is about to go as it is 5 years old and having trouble starting the truck so I go ahead and buy a new battery. (when the hell did batteries get so freaking expensive by the way?)
I double check and clean all the battery connections and put the new battery in and everything works fine.
So today I go to start it and no charging. I check for voltage at the battery with the engine running and it is like 12 volts. 12 volts at the lug on the back of the alternator too. I disconnect my 2 connectors that supply power to the alternator and they both have 12 volts. I plug them back in and still no charging. I wiggle all the wires and cables etc and still no charging. After the truck had been running for about 5 minutes I hear the alternator kick on and it works fine. Go to lunch and drive back home and still fine. WTF?
I guess my question is if there can be an internal problem with the alternator that is intermittent somehow?
I would just go buy an alternator somewhere else and swap them out to check but I don't want to spend the money right now.
Any suggestions?

 

[Rick the pool guy]

I've ran into this a couple of years ago
In the engine compartment (depends on the year) if the vehicle has a plastic red housing that says battery on it . Most likely the connection is corroded clean up and you should be good

 

[Rick the pool guy]

I've ran into this a couple of years ago
In the engine compartment (depends on the year) if the vehicle has a plastic red housing that says battery on it . Most likely the connection is corroded clean up and you should be good

I forgot to mention you should change your battery cables a bad cable will cause this issue to
Good luck I hope this helps you

 

[Flyin Brian]

Thanks Rick. I will do that.

 

[earlbrown]

Sounds like you got one bad out of the box. But only flakey instead of being dead as fried chicken.


What's odd is you keep seeing 12V. Usually when they fail, they go alot lower than that. ....unless you were reading battery power on the back of the lug.

If that's the case, you had a dead alternator and the voltage reading wasn't output, it was just a battery reading on the charge lead.


An easy test for that is to see 12V again when it's acting up, then turn the lights on bright, the fan on high, stereo, etc and put as much load on the battery as possible. If it stays at 12V, the alternator is just weak. If the voltage drops, the alternator can't keep up.

 

[Flyin Brian]

Hey Earl,
I am starting to think that it could be the new alternator.
I ran some tests this morning and actually wrote the results down and they are interesting.
It is about 40 degrees here this morning.
I measured the voltage with my good volt meter with the ignition off vehicle not running.
I got 12.4 volts everywhere. At battery terminals, post on back of alternator, under hood fuse box etc.
Started it up and the alternator was not running. I again measured voltage everywhere.
11.6 at battery and back of alternator with no accessories running.
11.3 at battery and back of alternator with headlights, dual electric fans, a/c blower, and rear window defogger all on.
I checked the voltage at the stock feed wire and my hotwire at the back of the alternator and both had voltage but still no alternator running.
I let it run for 10 minutes and the alternator finally kicked on. It makes some sound when it is running almost like a squeaking.
I measured voltage again with all accessories turned off.
I got 14.0 at the back of the alternator and 13.6 at the battery terminals.
Turned on all the accessories and got 12.7 at the battery and 13.0 at the alternator stud.
The alternator seems to get warm very quickly after it kicks in.
What is up with the .4 volt drop between the alternator stud and the battery positive?
With the engine not running I checked the resistance between the lug on the back of the alternator and the battery positive and it is almost zero so I figured the wire with the fusible link is good. Does the .4 volt drop while running mean this wire is weak?
Is my alternator bad?
I might take the alternator to a different auto store or to an alternator shop to have it checked. Or buy a new alternator from Oreily.
The current new alternator is one I got when I returned a 17 year old one under warranty to Autozone so it did not cost me anything yet. Just a bunch of time and a new battery that I needed anyway.

 

[Rick the pool guy]

Your alternator is controlled by the ecm so when the ecm picks up a demand signal it tells the alternator to turn on
You can do a simple test start the truck and put a demand on the system if the alternator doesn't respond ( give it about 30 seconds to 90 seconds)you could have a communication problem between the ecm and alternator (bad wire corroded plug or bad ecm) I ran into this in my truck

 

[Flyin Brian]

Does the ECM do that by supplying 12 volts to the "L" terminal at the alternator connector? I have verified 12 volts to the "L" terminal and it has a new connector. I also hot wired the alternator with switched ignition power to the "I" terminal at the alternator which you can do with this alternator according to Delco. Power to either one or both of these terminals should cause the alternator to switch on. I have also verified that the alternator has a ground path.

 

[Rick the pool guy]

The ecm acts like a on/off switch for the alternator. I would recommend pulling a wire diagram for your vehicle and see if you are getting correct voltage to activate the alternator

 

[Flyin Brian]

Thanks, will do.

 

[Rick the pool guy]

https://axleaddict.com/auto-repair/Alternator-Problems-Troubleshooting

 

[Rick the pool guy]

https://axleaddict.com/auto-repair/Alternator-Problems-Troubleshooting

 

[Rick the pool guy]

Sorry for the double post. This should help you out

 

[mikestertwo]

How many wires do you have on the connector on the back of the alternator? Mine has 3 wires. Orange which goes to +12v hot all the time...Red (L) which is a voltage output to the PCM....Gray (I) which is a duty cycle feed from the PCM to the regulator in the alternator. The gray wire is the one that controls the output of the alternator.

 

[Flyin Brian]

Thanks Rick. Good info in that article.

 

[Flyin Brian]

How many wires do you have on the connector on the back of the alternator? Mine has 3 wires. Orange which goes to +12v hot all the time...Red (L) which is a voltage output to the PCM....Gray (I) which is a duty cycle feed from the PCM to the regulator in the alternator. The gray wire is the one that controls the output of the alternator.

It had just 1 wire that connects to terminal "L". In the factory wiring diagram it passes through a resistor and the dash light.
I get voltage there at the alternator and the alternator still does not work sometimes. That is why I ran a switched hot wire to the "I" terminal which should also turn on the alternator. Still does not work all the time.

 

[Flyin Brian]

So I started it up this afternoon and no charging. I turned it off and removed the alternator. I took the alternator to Oreilly and it tested bad 3 times. This is the same new alternator that I got at Autozone and it had tested good at Autozone last week. So, I took it to a different Autozone than the one I got it at. They did not have the correct test lead to test the alternator but I told them that I had it tested at Oreilly and it tested bad there. I also told them that it did not work on the truck either. They gave me a new one.
I took it home and installed it and now it works fine. With the engine running and all accessories on I still get almost .4 volts voltage drop between the B+ lug on the back of the alternator and the battery positive terminal. That is higher than it should be according to the article Rick posted. I may still run a new heavy wire from the back of the alternator to the positive battery terminal to see if I can reduce this voltage drop.

 

[Rick the pool guy]

So I started it up this afternoon and no charging. I turned it off and removed the alternator. I took the alternator to Oreilly and it tested bad 3 times. This is the same new alternator that I got at Autozone and it had tested good at Autozone last week. So, I took it to a different Autozone than the one I got it at. They did not have the correct test lead to test the alternator but I told them that I had it tested at Oreilly and it tested bad there. I also told them that it did not work on the truck either. They gave me a new one.
I took it home and installed it and now it works fine. With the engine running and all accessories on I still get almost .4 volts voltage drop between the B+ lug on the back of the alternator and the battery positive terminal. That is higher than it should be according to the article Rick posted. I may still run a new heavy wire from the back of the alternator to the positive battery terminal to see if I can reduce this voltage drop.

Good job I'm glad you fixed it

 

[Flyin Brian]

I still had .4 volts drop between the alternator B+ post and the positive battery post under load so I ran a new heavy wire there and now have less than .05 volts drop. Everything seems fine now so I am gonna call it fixed. Thanks everyone for your input on this.
Brian