99 xj Alternator question?

Ok i have never replaced the alternator on my jeep and i assume its Original! ( 185,xxx ). I have a little system and would notice always that at a stoplight at night ( Or day with rear defroster ) the amp gauge would go from like 14 to 12 at idle when systems bumping. once you take off it would go back to normal. My Alternator always has had somewhat of a load wine to it. Tonight is the first time i have noticed this but when i started up my Cherokee it took like 30 seconds for it to go from 12-13 to 14 volts. Just like after 30 seconds it cut on. when i left the store it did the same thing, is it safe to say that my alternator is on its way out?. Also its like the 90 amp one. advance autos are 117 amps is that ok with out upgrading the wiring?

Thanks
JMOliver

And no i haven't tested it with meter or anything yet.

Also forgot all about this! A couple of months ago jeep wouldn't start and I had to wiggle one of the cable ends, been good since starting. Some days a little sluggish at first start up but after that always strong, I know battery is good it's like a new yellow top, think I might of answered my own question, hope so.

Comments?

How about your serpentine belt? What's it's condition? A slipping belt could cause your symptoms.

You can have the alternator bench tested if you're concerned or throw a meter on it and see what you're actually getting. The gauge on the dash is run through the PCM and I wouldn't consider it 100% accurate all the time. Tighten and clean your battery connections as Jeeps do not tolerate low voltage. Does your yellow top has side post or top posts? Make sure the connections are good.

The most common alternator failure is the brushes that ride on the slip rings. Eventually, they will wear down to the point that one, or both, of them is no longer making the contact required.

I have experienced alternator failure that were "solved" be tapping on the alternator case thus reseating the brushes. This is not a solution, it is a diagnostic. Brushes can be replaced and a good rebuild shop can order them in plus they can be found online. A person would need to have soldering skills in order to replace them. Takes longer to remove the alternator than it does to replace the brushes...

In the last year, I replaced my tired, old, had to be tapped on to make it work, stock 90 Amp alternator with a shiny new 200 Amp alternator. The purchase was made through one of the local shops here.

The feed line to the PDC was replaced and a 200A fuse was installed to replace the fusible link.

If your alternator seems to be charging the battery and is not dropping out periodically, I would check wiring and belt first before dumping money on it. If you had to jiggle a wire, assume that there is a wiring issue. Repair or replace any suspect parts. Clean all terminals. Make sure that you properly clean the battery posts and the insides of the battery terminals, because hard oxides can build up there and impede conductivity. Don't rely simply on a clean appearance. Make that lead shine.

Your XJ is reaching an age where brush wear and failure are pretty common. The brushes and slip rings are only used to energize the rotor, and do not pass high current, but if they begin to fail, you may notice that the alternator intermittently stops charging, and will, for a while, respond to sharp hits. If you do have to hit it, you have a short time before it's not enough, so shop for a repair or replacement now.

If you catch it in time, you can replace the brushes and be good for a long time. But sometimes the brushes will wear the slip rings unevenly, and though you can turn them down and get a little more life, the brushes will not last as long, and when they get very short they may pop out because the holders are no longer so close to the slip rings. You won't likely get another 185 K miles out of a turned-down alternator.

Assuming your wiring is good, increased amperage should be no problem.

if your amp is strong enough to dim your lights or dip your voltage gauge you need to have a capacitor installed, over drawing the alternator's output capabilities is a quick way to ruin it.