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Does this mean my alternator is goin bad?

Ben824

NAXJA Forum User
Location
Woodstock, GA
97 XJ 4.0L auto 4x4 ok first thing this morning I look down and my check gauges light is on and my voltage level gauge is reading nothin but the Jeep is running fine. Then as soon as I get to where I am going I shut the Jeep off and let it sit for a few seconds and then I turn it to the "on" position and the gauge reads like normal 12 volts roughly. Then I start the Jeep back up and then gauge still read the exact same and I thought I remember it going up to close to 14 once the engine was running. So what's goin on here? Bad sensor? Alternator goin out?
 
Re: Does this mean my alternative is goin bad?

Could be alternator going out, perhaps brushes (there seem to be a lot worn out brushes showing up on this forum recently). When this happened on my 99, I noticed an odd thing: for a period of time after the alternator stopped charging, the voltmeter would read the reduced voltage, but after a couple of minutes, it would drop to zero and the check engine light would come on. This is not a sensor failure, but the way it operates, I'm guessing in order to warn you that this is a true charging failure and not just a temporary heavy current draw. After it's sat for a while, it resets and the voltmeter reads again, until either the alternator stops charging again or the built-in time delay is exceeded again, whereupon it will drop to zero and set the CEL again.
 
Keep an eye on it.

Could be the alternator starting to go south, especially if it is the original on a 97.

The other wildcard in a charging issue is the voltage regulator which is located inside of the computer, but the alternator itself fails way more often than the VR in the computer does; they are quite hardy.
 
Well it is the original alternator and with how often these things go bad on these Jeeps I am surprised it made it this long after all I have put it through.

It has gone back to normal now. I came back to the Jeep started it up and it went right to 12 volts and hung there for a minute and then slowly moved up to the normal position just slightly under 14 volts and fluctuated ever so slightly but held pretty steady and normal. I am hoping it doesn't go bad on me because I really don't want to drop the cash to replace it right now.
 
Just changing mine tonight - been acting up for a couple of weeks.

If it's reading 12 or less - it's not charging. Mine is worn brushes. It will read only battery voltage on startup, then after a minute or two just pop up to the normal 14. If it doesn't start running on it's own after a few minutes of driving, I pull over and give it a tap with a hammer to get it going.

The time before it starts running has been getting longer, and the taps are no longer taps. It was either finally swap it out or get a bigger hammer.

I got a rebuilt for $90, but I could have just picked up some brushes if I was working on the cheap this month. Changing the brushes will work if you are tight for cash, it just won't last as long if the slip collar is worn or gouged. It's not really a hard job to replace the brushes.

BTW, best place I found to wack it to get it working again is from below -right on the lower mounting bolt - swing from back to front.
 
If your problem is the brushes, it would pay to take the alternator out and remove the brush holder (fairly easy) and inspect the slip rings. If they're not badly gouged up, it's worth replacing the brushes. You need to solder them in if you get just the brushes without the holder. If you need a stopgap it might still be worth doing even if the slip rings are bad, and that will give you time to shop for a better deal or to price rebuilds.

You can clean up a slip ring with something very mild like crocus cloth if it's scorched, but don't use sandpaper or the like, or it will eat brushes.
 
Well since my last post it started acting up again. But the weird thing I have that is going on is now when I start up it goes to just a tad below the 12 volt mark of right on it. Once I really start moving it drops down to just off of the 9 volt mark and stays there and give me the Check Gauges light but no Check Engine light.

Does this still mean I am having alternator problems or the previously mentioned voltage regulator?

Also when I went to autozone they had 90 amp alternators and 120 amp alternators. Did any XJ come with the 120 amp? Clearly the 120 would be a nice upgrade but if they were stock options on some then I would like to know if I have the 120 because I want to make sure I am not downgrading what my Jeep has. I do have a bunch of stuff installed in the Jeep like lights, CB, sound system, etc. and I want to make sure I have an alternator that can keep up.
 
Try removing your battery cables, and cleaning any corrosion that may have built up, and then reinstalling them tight. I know I've heard of this problem happening before, as well as I've had the same issues pop up once before, and haven't had it since.
 
You are rapidly approaching the moment of truth--a long walk or a tow truck bill.

Your battery isn't charging and its running down. Once available voltage drops below 9 volts the engine management--computer, sensors--is going to turn to crap on your XJ and leave you stranded.

Carry a hammer and a long screwdriver or chunk of metal rod/broom handle and when it screws up hit the alternator with the hammer or hammer and rod/stick combo to try and kick it started. This is a last ditch stop-gap, you need to fix it ASAP. Or pay for AAA. Or wear real comfortable walking shoes.
 
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