carbuff

So, I bought the xj a month ago. It needed an alternator. Got one from advance with the $40 coupon online. Cost me $75 lifetime warranty. Working great for a few weeks. In the meantime I upgraded my headlight harness and headlights to the autopal housings with the stock 55 watt bulbs that came with it. All still working fine. So, last week I start to notice little drops of coolant on the ground. I inspect the situation and its either the water pump weep hole or the coolant tube that comes from the waterpump. I immediately think that I may have overtightened the belt and ruined the bearing in the pump so I backed of of it a bit. It still seemed pretty tight. Turns out the leak is the bypass tube, pinhole leak that starts to spray coolant all over the front of the motor in the belt etc. So I replace that with a 5/8 nipple and extend the heater hose and all is fine. No need to remove the pump, thats how the factory should have done it. On a side note, the tube rusted from the outside. It looked horrible on the outside but the inside was as clean as the day it was new, the whole system is very clean inside. Anyway, so Im driving home that night and my check gauges light comes on and the needle plummets off the scale. Damn, not the alternator again. If I shut it down and restart it, it goes back to normal until I turn on the lights or the heater on high, defroster, etc. I also notice that it makes this weird squeaking chirping sound before it quits. So I do all the free stuff first, clean all the grounds, etc. Same problem. Then it hits me, maybe the belt is slipping on the alternator. I did loosen it and it had coolant sprayed all over it too. Maybe the chirping sound was the belt slipping. So, today I tighten up the belt and start it up and turn the lights on and drive it with the lights on and all accessories on too. No problems. So, now here is my actual question. With all the accessories on, everything is fine unless the rpms drop below 800.Then the lights will dim and the needle drops to just under 12v. If I kick it up a bit to like 1000 it goes back to 14. Is this pretty much normal for a stock alternator? I would not even think about it if it were not for the dash gauge. Ive had plenty of older cars where the lights dimmed a bit on really low idle. Its only with all the accessories turned on at once. With lights alone its fine. Is this normal for the stock wimpy alternator? Sorry for the book.

PocketsEmpty

As a general rule of thumb you should get your new alternator tested before you even leave the store. What about your battery? Get that tested too. Also, I hope you upgraded your headlight wiring harness along with the new lights!

carbuff

Yes, as stated in OP the harness was upgraded. Also, I dont know where you guys go that they will test all your stuff. My local advance just sticks a multimeter on the battery, I saw a guy have this done, he was kind of dumbfounded as if to say, hell I could have done that. Also they will not read codes either, they refer you to a local mechanic shop for that. Maybe its a NY thing, we have all sorts of weird liability laws here. They will install your wiper blades though. Ive seen that. But, back to point. Is that normal behavior for the stock alternator? To not be able to keep up with all the accessories on at once at very low idle? I know guys are always looking to upgrade to a better alt so I figure it might be normal.

PocketsEmpty

What's the output of the alt? Definitely not normal. Sorry I missed the part about the harness somehow. Crazy that they won't test your stuff properly. My jeep had a 117a alt I believe

carbuff

The alt puts out 13.5 to 14.3 depending on load. The only time it dips lower is if I have all the lights and accessories on at the same time and the engine is idling low, then Ive gotten readings of 11.8. As soon as the idle increases it goes back to 14 or so. It may be that this is typical for this unit and Ive only noticed it because Ive been keeping an eye on this since Ive had the problem. If its normal, I dont mind but I just wonder if its an indication of the new alt failing.