ltcollange

hey guys.. i'm the guy with a bad intake valve awhile ago I got fixed! :P well now an interesting different set of events.. my battery light came on the other day (and yes it is an undervolt @ 12.02V). however; I charged my battery and it checks good @ 13.2v and took my alternator off and down to have it bench tested. it's good at 14.69v. now I cleaned up all connections to the alternator and grounds, and terminals (I even got new terminals cause I know those cheap lead ones always have problems). I noticed on the 4.0 alternator doesn't have a plug in (+B) like most vehicles. It has 4 eye hole connectors that are fastened by bolts (yes I cleaned those up). now when I cleaned them up everything worked fine for two days. then battery light came back on. Now my question is what could it be that's causing the undervolt?

Thanks

Radi

First thing I'd do is put a voltmeter on the battery when the light comes on and see what you have. We'll know if it's an actual problem or just an indicator problem that way.

ltcollange

i did.. it doesnt come on at first which is strange. but it reads at 12.02 on startup and about 11.95-12.05 when the light comes on...

Turbo X_J

Why did you have to charge the battery, has it been load tested?

ltcollange

yeah it tests fine when fully charged.. it's also only 3 months old. but because somewhere is discharging the battery was dying because of it.. so i spent all morning cleaning and re working some of my grounds and cleaning all connections.. here's to hoping it works now

Roler

Have a look at these videos (links below). Might find that helpful.
Your alternator good and battery test good but your battery is not being charged properly> the actual wiring between them should be checked. Good instructions on this and checking a charging system.

http://www.ericthecarguy.com/electri...id=FTGz0PKIl84

http://www.ericthecarguy.com/electri...id=ZuumBVz6WOM

ltcollange

I checked all the wiring. it's all about 1 ohm. appreciate it.. im gonna charge it to max @ 13.2 then take it to autozone.. i have a feeling the voltage regulator may be bad.. which is gonna suck. it's in the PCM

ltcollange

i have a feeling it's the voltage regulator. i've done every single test in every wire in the starting/charging system. everything is reading as it should. and to of double checked. i cleaned every connection to every wire. that's the only thing i could imagine it being now

Turbo X_J

One has to wonder why it "worked fine for 2 days". When anything electronic goes out, it's usually for good, still sounds like a wiring issue.

ltcollange

that's what I thought as well.. but I literally spent 3 hours checking resistances in all the wiring.. including turning key to start and checking signal wiring to starter. the wiring diagram in the book is a pain to read but I eventually figured it out.. did a voltage drop test, negative test, everything is checking out exactly the way it should... the only thing i havent done is pull the pcm out to clean the connections there. that could very well be it. but then I gotta pull the battery out for the 3rd time today. lol!

Roler

Just thinking: isnt there a battery temp sensor something in the battery tray underneath the battery, that also relates to the charging capacity/characteristics (not sure what year yours is, my 97 post update has one).

ltcollange

ya know roler.. I don't really know. i'll go check it out

bulrid8

Did you ever get battery load tested?

captainwoot

For what is worth, when i had my 98 i had similiar problems. i went ahead and took the alt apart and the brushes were worn out, one of the slip rings on the armature was almost gone as well.
Mine bench tested ok as well, and when the batt light came on it was still showing 13.5 at the battery....regulator failures in the pcm do happen but not that often
Good luck!

carbuff

Yup, I had similar problems with my 2000. Went crazy checking grounds and such. Replaced the alternator and all is well again.