hello, im a noob to this forum and recently my jeep has a low voltage problem. When I start it the voltage gauge is right between 9 and 14 (where it should be) and it takes a few minutes for it to get to normal operation. I can only run either the headlights or the heat,when I run both the gauge drops (sometimes to 0) until I shut off the heat or the headlights. I already replaced the belt and tensioned it to spec. which had originally stopped it for a few days. now its back. what could it be? the alternator? all advice is welcome and I don't want to be just throwing money at. thanks in advance.

 

Welcome.
1) verify you batt voltage with a meter
2) have your battery load tested

Looks like your battery has issues holding a load (...) and/or not charging properly.
If the battery tests out good, we look further (alternator, charging system, connections etc)

 

I took it to Advanced yesterday and everything checked out okay. alternator and battery was load tested. but also when I took the jeep up there the voltage gauge didn't drop a bit for them, it acted like everything was okay. so I think it slid through the test.

 

Have you cleaned all the electrical connections? Battery terminals, battery grounds, and the grounding cable at the back of the valve cover going to the firewall?

Then check the alternator + connection for corrosion and that the belt is properly tight and not slipping. After that, you can pretty much safely assume its the alternator going out (if the battery is 100% confirmed good).

Pretty cheap/easy fix, but I would recommend taking the time to upgrade to a larger alternator while you are under there anyway.

 

Disconnect the battery first, before playing with the electrical system, you'll be glad you did.

 

took your advice and this morning I pulled it into my dads shop looked at all the connections they were all checked and cleaned there was nothing out of the ordinary and to no avail. SO now that that's out of the way. im going to replace the alternator I thought about going to a bigger one, now the next question is do I need to replace anything else to handle the bigger alt? or will everything else handle it fine? thanks for replying!

 

So, you say it tests ok, but you decide to replace it...?

If both your battery and alternator seperately tests ok, but not when working together, I'd start by checking the connections between the two.

Measure voltage with and without engine running.

 

Not as fun as just replacing stuff.

 

Yeah, you're right, why the h#ll checking and testing stuff...?

 

New belts stretch and usually have to be re-tensioned after a bit. Do you get any noise at all from the belt -- even a brief chirp or squeal?

Since it was okay for awhile after you replaced the belt and then went south again, I would tighten a bit more in small increments until everything works and no more.

People obsess about over tightening the belt and rightfully so, but I just tighten mine in small increments until its right and I've never had a bearing failure (guaranteed to have one now I guess!). Tensioning gauges are good but I've never had one and the 4.0 belt has to be so tight that I'm not sure they are really needed.

 

He said it tested OK at autozone. Mine did as well, but it would not charge over 13.2v in real life, and sometimes it would not charge at all wihch was worrying.

Definitely do a basic alternator test (measure batt voltage @ rest, @ idle, with all accessories on @ idle, and with all acc. on @ 1500+rpm.)


You dont need to replace anything when going to a bigger alternator (per-say). The ZJ alternator drops in with some very minor grinding to the alternator mounting bracket, and the engine block (search for these threads, there are a million of them).

You will want the alternator out of a 2003 Durango I think (they have 136 and 160 amp versions of that alternator).

I would highly recommend upgrading your charging system wiring though. Stock XJ wiring is a joke, and it makes a huge difference to the overall capability of the charging system.

And definitely make sure the belt is not slipping. I would tighten it up some just for testing so you know it isnt the culprit. Its always about minimizing how many times you need to go to the parts store for me

EDIT:
https://www.cherokeeforum.com/f67/up...pplier-187743/

 

I do get a little chirp on start up when it stays between 9 and 14. then when it warms up on 14 it doesn't make any at all. until im driving using both heat and headlights then the guage drops and I wouldn't say its a squeal or a chirp. its more like a ping noise. I will recheck the tension and tighten it up to see if stops. but its already pretty darn tight though..

 

Pretty darn tight plus, pretty much describes the 4.0 tension. Standard procedure per the book is to recheck tension on a new belt after a few minutes running. Tighten it a bit regardless of what the gauge says. You can always relax it a bit later

Not sure about a "ping" noise but let's see what happens.

 

update: re tensioned the belt which did help dramatically, it makes no noise whatsoever. but I still get some voltage drop when driving (not nearly as bad). im taking it to Bulldog battery tomorrow for one more load test. I will report back to my finds..

 

So how far does it drop and when (under what circumstances) does it do this....?
A little drop when your AC clutch comes on for instance, is normal.