• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Charging System - Bizare Problems: Alternator?

88JeepXJ

NAXJA Forum User
Location
MA
OK so my '99 started acting up yesterday and I'd like to get some advice from you guys.

I come to a fairly sudden stop yesterday and as I accelerate I notice "Check Gauges" light is on and I look to find my volt meter pegged at "zero"...technically 9 volts but it doesn't go below there so...

I pull over, turn the Jeep off, wait a minute and turn it back on. Cranks like normal, fires up, and volt meter goes to 14, great no problem. Drive 15 minutes to dinner.

Then after dinner the check gauges light comes back on and volt meter back at zero. I drive all the way home but I THINK my headlights were dimmer than normal. I check voltage at the battery and it reads 11.8 volts across the battery at idle. It is late and cold and I don't want to deal with it so I stick a charger on it over night.

Check battery this morning and it is 12.8 volts. Start her up and all is well. 13.8 across the battery and the gauge is showing 14. Driving to work and nothing out of the normal except that I need gas. So I stop get some gas and when I start her back up gauge reads 12 volts! WTF? I continue driving to work and all of a sudden the gauge drops and light comes back on!

So WTF? Is this just the alternator going out or is it something more annoying?
 
Yup, sounds like the alternator, specifically the voltage regulator but with your vintage that's done internally so just get the whole alternator...
Hope that helps.
this statement is incorrect, the 99 voltage regulator is in the ECM, not the Alt, but still your alternator could be on its way out. Also check for a bad ground, check your connections and fuses too.

most parts stores offer free alternator testing, you just have to take it out of the vehicle and bring it there
 
The alt's going out I just had 2 go out on me in my xj in the past month. Put in the 136A unit from a grand and no worries.
 
The alt's going out I just had 2 go out on me in my xj in the past month. Put in the 136A unit from a grand and no worries.

ZJ? Any particular year? 4.0 I'm assuming...

If I'm going to take the alternator off to have it tested I might as well just get a new one to put back on.
 
You have the Delco integral unit. I've got to believe that the ZJ has a different system more like the later XJ's with the regulator in the PCM. You wouldn't want to change to that. Too complicated. If you search in the forum more, I'm sure you can find out about heavy duty versions of the Delco unit.
 
Some of you may be confusing my name with my current xj. I have a 99 not an 88.

I think starting in 99 the xj got the 117 amp alt like the zj...that's all I can find for my year. 98 and older gave the 90 amp.
 
Post Renix--87-90--you will have a Nippon Denso alternator with PCM charging control.

First, you need to clean and test your battery cables and your grounds. I would have the battery load tested too. When slamming on the brakes seems to have triggered the problem, I would be looking for a loose connection somewhere.

NOTE: many reports on NAXJA of "parts store" alternator tests where the Nippon Denso tests good, and yet they fail. Recommend you take it to a competent alternator shop for testing off vehicle, or to a competent mechanic for on vehicle testing.
 
I took it to Autozone for S's & G's and they said the test showed the alternator was not charging. I picked up a reman. 117 amp alternator while I was there just in case I need to swap it out tonight/tomorrow.
 
If their test show's it's not charging and you already have it out then why not throw the new one in when putting it back together rather than throwing the bad one back in.
 
This is exactly what happened to my 99, and the problem was worn out brushes in the alternator. It took me a while to figure this out because of the way the gauge behaves. Here's what's happening:

The voltmeter will read correctly down to about 9 volts, which is what you'll be running under normal load with no alternator output. When it reaches that point, it will only read for about 30 seconds, and then drop to zero and set the check light. Even if the alternator recovers then, it will stay at zero until you restart. Bad brushes will start to announce themselves by cutting out periodically, and if you don't catch the voltmeter in transition, you won't notice. You'll see the meter at zero, even though the alternator has started charging again.

I didn't figure this out until I was driving in the evening and actually saw the lights dim. It caught back on if I revved it, for a while, but as time went on the lapses were longer, and eventually it didn't come back until I took a stick and hit it.

I add this even though the problem here may be fixed, because I don't think that feature of the voltmeter is documented anywhere. It seems a nuisance at first, but it is, in fact, a valuable early warning for intermittent failures that might otherwise be missed. Since the most typical such failure is worn brushes, I'd look there first. It's pretty easy to get the brush set out of a nippondenso.
 
It was the alternator. Pulled it out and looked at the brushed...one brush was 90% gone and the stator was all chewed up!

Got a reman. 117amp alternator at AutoZone. All it well again.
 
Back
Top