Help: alternator info

[delong_1]

ive been having some issues with my charging system, tested the battery. it was a pos, replaced it and the volt meter on the dash was still reading low, i checked it and at the time it was only at 13.1x volts idling. i drove it home and it got as low as 10 volts, so i assumed that it was just the alternator giving up on me. got a new alternator and now it still only shows approx. 13 volts, it has always shown over 14 volts. is there something else i might be missing that could fail??? i would appriciate any help here, thanks

 

[Chevy1925]

If you put a digital volt meter at the batt with it idling, what does it show? I trust our gauges with a grain a salt

 

[delong_1]

i used the tester that tests the battery and charging system, thats when it showed 13 volts.

 

[Chevy1925]

Would it change with rpm? What does it read with the new one on now

 

[delong_1]

no change with rpm at all, it is still at 13 volts even with the old gm battery with 400 cranking amps it was always at 14.1x

now its got two new gm batteries, and a new 130 amp alt. and still low voltage?

 

[JoshH]

Does the voltage go up at all when it is running? Have you checked voltage at the alternator?

 

[Chevy1925]

Try back probeing the 12v excite wire for the alt with 12v direct from the battery off the positive post. I dont remember what wire it is but ive read about a few truck that have issues getting enough voltage to the regulator to excite it fully. (Boy that sounds wrong)

 

[delong_1]

well i guess i will try that tomorrow and see what i find

 

[delong_1]

Does the voltage go up at all when it is running? Have you checked voltage at the alternator?

ya, it was 12.xx volts with the key off. and no i didnt check voltage there

 

[chevyburnout1]

Is there any codes stored for the glow plugs? Specifically P0380? I know this sounds odd, and have yet to see it in person, but their is a document out from GM stating if it doesn't see voltage on the glow plug feedback circuit it will shut off voltage to the exciter field circuit for the alternator... Something to look at. But like I said I have yet to see this personally.

 

[delong_1]

no codes

at startup i am getting 13.7 volts and it will go down some, this is at the stud on the alt itself. at the connector i probed it and im only geting 10.6 volts is this were my problem is??

 

[Chevy1925]

no codes

at startup i am getting 13.7 volts and it will go down some, this is at the stud on the alt itself. at the connector i probed it and im only geting 10.6 volts is this were my problem is??

eh it could or couldnt be. the last truck i just worked on showed the same for the excite wire. my issue wasnt the same as your talking though. He was having issues with flickering interior and exterior lights. what kind of batteries did you put back in it?

 

[delong_1]

the grey wire which should be the duty cycle wire is the one with 10 volts, the other which should be the charge indicator control wire had like 2 volts???

i put in 2 new ac delco batteries and for laughs i tested them they both showed over 870 cca, and 100% state of health

 

[THEFERMANATOR]

What year? Check to make sure none of teh pins are pushed out of teh bail connector. If it is an LB7, the ecm supplies the inputs for the alternator to charge I believe. it doesn't control the voltage, but does control when it fields. The regulator in teh alternator controls teh voltage, and many aftermarket units are set to only charge at 13.2-13.5 where the stock ones will charge at 13.8-14.5.

 

[delong_1]

It's an 01, nothing had been changed for a few weeks and the problem just surfaced

All symptoms are the same as when it had an old single battery and factory alt.

 

[Chevy1925]

You might try swapping with a known good truck if you can. The truck that had the flickering light issue had a brand new batt in it, it was 3 months old from oreilys. after replacing the alt and having that fix part of the issue i swapped in my battery from my truck and his issue went away. he took it to oreily and they tested it showing it was perfectly fine, same with the alt but as soon as they tried another batt from their shelf, issue went away.

im wondering if your alt might be starting to lay over a bit. Ill tell you this much, i was running Gm 12si alternators in my samurai for more amperage. i would constantly go through alts every few months and couldnt figure out why. i finally started dismanteling them and found the chinese brushes they were using have a hole just at the end of the brushes to hold them down for assembly leaving about a 1/8th inch of brush before it would wear to the point of breaking there or loose contact. two of them snapped the ends off the brush at the hole and actually broke one of the three posts that feeds AC current into the regulator/converter.

I no longer trust any alts from NAPA, Autozone or Oreilys. id much rather take it down and have a shop i know rebuilt it.