Odd alternator problem

Ok, 99XJ 4.0 Auto.

3,000 miles ago I put a new Napa alternator in my truck, worked fine no problems. The other day it was acting funny dropping near 12v and back upto 14 while crusing, eventually it died. I got another one warrantied.

This one works fine, but with the headlights on and the blower on high it drops down to 12v when the E-fan kicks on. My original and second alternator would hold 14 all the time, with everthing running (blower, two 100w highbeams, 300w of driving lights, rear defrost and blower) I could get it to drop to 13V.

Its not the gauge, a multimeter at the battery (fully charged btw) with all accessories on it will drop down to 11.9V. I know its a very large load but before it didnt do this. With the defrost and regular headlights on you can hear the blower motor slow and see the headlights dim noticeably when the efan starts.

Ive checked all the grounds I could find, cleaned all connection with no avail. Is it just another junk alt?

Nope, sounds like your PCM is not controlling the alternator as it should, or your battery is bad.

Fully charge the battery and have it load tested. Drive to a shop and have them test the charging system, don't rely on the parts store dude.

i had crap zone alts to this. also have you upgraded you battery and alt wiring? with that amount of a load i would recommend doing it. my alt is startin to do this too. i know its a good fully charged batt. im runnin a brand new deep cycle batt and let it sit on charge over night. might also want to look at higher amp alt. could also be the internal regulator inside the alt.

I work at a garage and load tested it and it came out to 720CCa, its a 770CCA battery. Test after i charged it all morning.

Getting pretty frustrated with this, im tempted to get another alt, throw it in and see what happens.

i have gotten bad ones from parts stores i have to warranty mine again too just havent had the chance yet

summitlt said:

I work at a garage and load tested it and it came out to 720CCa, its a 770CCA battery. Test after i charged it all morning.

Getting pretty frustrated with this, im tempted to get another alt, throw it in and see what happens.

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I don't have the FSM for the years with Nippon Denso PCM controlled alternators so I can't help with testing procedures for the alternator in your 99. Maybe someone else can chime in.

That said, what were the symptoms 3000 miles ago when you first replaced the alternator? You said new, but was it a reman?

If it was a Renix with a Delco Remy CS-130 there would be a fusible link in the cable from the alternator to the starter relay's PDC lug. I think yours would have two 60 amp maxi fuses?

Check your main cables with an ohm meter, resistance should be near ZERO. Check your grounds to--firewall and fenderwell.

Pick up a set of 5-90's upgraded batt cables.. Some of the best coin I have spent!

The battery cable upgrade is a wonderful improvement. Add an extra ground from the passenger side block to the fenderwell and it's even better. BTW, did you refresh the factory ground connections yet?

Cleaned all the grounds i could find. The original factory alternator bearings were starting to make noise is why i changed it in the first place.

I wonder if this could be related: http://naxja.org/forum/showthread.php?t=1028795