Alternator charging issues

[Les W]

Hey everyone, before I drop some money on parts to chase this problem I thought I would see if anyone has seen this issue or some suggestions. My thought at this point is to swap Alt. Prob started about a year ago very intermittent where the ammeter would show a discharge while driving but when you turned off the key and restarted problem went away, now its here all the time. Putting a meter across battery I get 12.6v Start vehicle and get 14.+ which drops down to normal within a few minutes. Once you start driving the voltage on dash drops. I have measured volts while running and it is discharging and I am getting 12.85v while charging which I thought should be 13.1 min. I had a couple different auto places check and got a response that battery had 1/4 life so I took battery and swapped for new 42 mo Delco at dealer. Still having same issue. I cant see spending a hundred or more at dealer if I can put that towards new Alt. This is a orig Alt in a 08 Denali with 82000 miles. Any diagnostics I might be missing or suggestions would be appreciated. Thanks for any help

 

[PG01]

Its normal for these trucks. Its called rvc. Regulated voltage control... basically shuts alt off when cruising but turns it back on when needed. Its to save gas... i know sounds crazy but its true. Look it up. If you have a tow haul button, leave it tow mode and it turns it off. Or, on your neg battery cable is a small electronic current sensor and if you disconnect it you should keep a more steady voltage.

 

[Les W]

Its normal for these trucks. Its called rvc. Regulated voltage control... basically shuts alt off when cruising but turns it back on when needed. Its to save gas... i know sounds crazy but its true. Look it up. If you have a tow haul button, leave it tow mode and it turns it off. Or, on your neg battery cable is a small electronic current sensor and if you disconnect it you should keep a more steady voltage.

 

[Les W]

I have heard that but first time I have seen it in 3 yrs. With 100 deg heat and around town driving I didnt think it would be conserving but maybe overworking.

 

[swathdiver]

Les I know how you feel. I think that you'd enjoy having your own Tech2 to check out the things going on inside your truck. You can also download the restoration manual for the GMT900s from the GM Heritage website and learn even more details in the various pdfs located here: https://www.gmupfitter.com/pdflists/view/6

Consider a subscription to AllDataDIY and or the purchase of the manual in pdf form by either download or DVD/CD from SeriousCTBuyer on ebay.

You'll find RVC and EPM very interesting technology.

 

[Doubeleive]

ya mine does it as well even with two AGM batteries, don't like it but whatever......GM

 

[Les W]

ya mine does it as well even with two AGM batteries, don't like it but whatever......GM

So does your guage look like mine? I wont be so worried if I knew someone else looked the same. Also I would like to see some pics of your dual battery setup. I have been wanting to do a dual battery with isolator for mine.

 

[Les W]

Les I know how you feel. I think that you'd enjoy having your own Tech2 to check out the things going on inside your truck. You can also download the restoration manual for the GMT900s from the GM Heritage website and learn even more details in the various pdfs located here: https://www.gmupfitter.com/pdflists/view/6

Consider a subscription to AllDataDIY and or the purchase of the manual in pdf form by either download or DVD/CD from SeriousCTBuyer on ebay.

You'll find RVC and EPM very interesting technology.

Thanks for the info I will look in to it. I could fill my library with tech manuals. You have mentioned on more than one post about the Tech2, is that something you are connected with, I would like to learn more. I have the Actron 980 but dont think it is as in depth as the Tech2.

 

[Doubeleive]

So does your guage look like mine? I wont be so worried if I knew someone else looked the same. Also I would like to see some pics of your dual battery setup. I have been wanting to do a dual battery with isolator for mine.

yes my volt meter will vary, I have the stock 2 battery setup just like the ppv's, all you need is the battery holder which is the same as the on the nbs's and the battery cable and then it's cheaper to make your own ground(s)
battery cable is $60-65
https://www.ebay.com/itm/ACDelco-GM...921435&hash=item43fcfddeb7:g:CBUAAOSwkNZUkWJV
the holder is only a few bucks
https://www.ebay.com/itm/GM-Battery-Hold-Down-Tie-Bracket-Clamp-14005061-OEM-Replacement/253591032890?fits=Year:2000|Model:Tahoe&epid=655209434&hash=item3b0b34143a:g:~v0AAOSwD99aydfH

the cable goes under the rear of the engine and clips right into the existing holes and connects to the starter, then you just run a ground to the frame and one to the alternator bracket.

 

[PG01]

1 change above to wes’s post.. cable goes along the ‘front’ of engine instead of ‘rear’.....it ws late and he was typing fast. Ground cable can be purchased also and goes from battery direct to alt bracket. I got all gm parts from amazon and my gauge does same, up and down.

Positive cable is in lower wire loom directly under the larger black plastic channel and actually clips (wire loom and clips come with cable) right into that channel from battery to starter.
Good luck. I think Wes posted all part #’s
There are posts on here of an isolated setup but this is a parallel type.

 

[swathdiver]

You have mentioned on more than one post about the Tech2, is that something you are connected with

No, just recognize it as an essential tool. Without it you're really guessing. Wish I'd bought it twelve years ago, would have saved me a lot of money and frustration. When I bought this truck the Tech2 was part of the budget this time. It's already paid for itself several times over.

 

[Doubeleive]

1 change above to wes’s post.. cable goes along the ‘front’ of engine instead of ‘rear’.....it ws late and he was typing fast. Ground cable can be purchased also and goes from battery direct to alt bracket. I got all gm parts from amazon and my gauge does same, up and down.

Positive cable is in lower wire loom directly under the larger black plastic channel and actually clips (wire loom and clips come with cable) right into that channel from battery to starter.
Good luck. I think Wes posted all part #’s
There are posts on here of an isolated setup but this is a parallel type.
View attachment 200892

 

[harbison]

I've owned mine since new. Now has 225K on it. It has always done that and I've never liked it but that's the way it was designed. Like the AFM, it's another attempt to hit those EPA mpg numbers. Don't worry about it. It's normal.

 

[Floep]

In the first place it is a "volt meter" Not an Ammeter,. It does not show charge or discharging, just how high the voltage is. The battery requires different voltage depending mostly on how low the battery is when you are reading it. In cold surroundings it needs to be higher than in warm ambient also when you used a big gulp of power like right after a start it will give a higher voltage to recharge the battery fast and soon goes to a maintain voltage. All this compliments of the computer. Gives longer life to the battery and slightly better mileage, in other words don't worry, be happy, it is very normal.

 

[89Suburban]

Mine does the same thing, glad this thread popped up. I just drive it and phuck it lol.

 

[Les W]

In the first place it is a "volt meter" Not an Ammeter,. It does not show charge or discharging, just how high the voltage is. The battery requires different voltage depending mostly on how low the battery is when you are reading it. In cold surroundings it needs to be higher than in warm ambient also when you used a big gulp of power like right after a start it will give a higher voltage to recharge the battery fast and soon goes to a maintain voltage. All this compliments of the computer. Gives longer life to the battery and slightly better mileage, in other words don't worry, be happy, it is very normal.

 

[puckhead]

No, just recognize it as an essential tool. Without it you're really guessing. Wish I'd bought it twelve years ago, would have saved me a lot of money and frustration. When I bought this truck the Tech2 was part of the budget this time. It's already paid for itself several times over.

Do you recommend a specific one?

 

[swathdiver]

Do you recommend a specific one?

The older ones still command a high premium, those made by OTC and Bosch. I believe Vetronix was the last company to make them and then the Chinese factory started selling them on their own or something like that. These can be had for $300-400 on ebay now. Make sure it has that latest software, 33.004 and the Candi module for use with GMT900s. Many of the other items are for self diagnostics and other vehicles and programming modules. The software discs, the old TIS2000 software I don't think necessary for GMT900s, I don't bother with it after installing onto an old laptop. If I have to program a module, I'll buy the 3-day subscription off Tis2Web. But for everyday useage, looking at things, resetting codes, etc. such is not needed.

I got mine with the case and glad as it keeps everything together and can get knocked around in the truck and be alright.

 

[puckhead]

Thanks! I saw that Bosch had a few options at Orielly's the other day. They had one priced at $90 I think and three more options up to about $350 IIRC. Don't have the cash for the expensive one right now but it looked nice!

 

[swathdiver]

Thanks! I saw that Bosch had a few options at Orielly's the other day. They had one priced at $90 I think and three more options up to about $350 IIRC. Don't have the cash for the expensive one right now but it looked nice!

It's hard to justify when money is tight, I surely know that, but these things pay for themselves in short order in money not spent on repairs, throwing parts at a problem because we now have a proper diagnostic tool. For example, two different actuators on my AC got out of sync at differing times and threw codes and the AC blew warm. The Tech2 was used to put them back into order. At $80 each plus labor, that adds up to a pretty penny.