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4.0 voltage issue

2

2001BlackonBlack

NAXJA Forum User
Location
Denver Tech Center
So here is the story, my volt gauge was acting strange moving from 14 volts down to 0 and stopping there. So last week I replaced the alternator and upon starting the jeep I could smell the new alternator burning up, which I did not smell prior to replacing the old one. Soon after replacing it I have the same problem again and it seems that I'm burning up this new alternator.
I look forward to your help and will address any questions about this problem.
 
It could just be the new alternator warming up for the first time, assembly lube etc.

If your battery was either slightly or completely drained the alt will have to work alot harder to bring it back up to par. So, make sure your battery is - a.) good, load test etc. and - b.) properly grounded and/or c.) fully charged before you hook up.

I'm by no means an electrical guru, maybe one of those guys will chime in.
 
hi im the electric guru... i will tell you this, the alternator is controlled by the computer in your jeep, its not self controlled or regulated.

how is the voltage meter lookin on the dash? if its always staying at 14 or about that then i wouldnt worry about it.

also keep dirt sand saltwater and other stuff from gettin in there while off roading im on my 3rd alternator in two years due to that stuff.

hope i helped
 
Why did you replace the alternator? Did you use a test light or meter to narrow down the problem and diagnose the alternator as the fault? Lots of stuff in that system can cause your volt gage to display zero. Loose grounds, poor connections, etc. I'd do some testing on it before I threw money at an alternator.

Start with the basics. Check battery and alternator connections to see if they're clean and tight. Check to make sure you have a good battery, voltage-wise. Observe lights and accessories to determine if they go dim or fail to operate when the problem occurs. Then pull out a schematic of the charging system, including the computer, and start figuring out when it is or is not supposed to charge. Do you have an FSM or something with wiring diagrams in it?

That's where I'd start.
 
Also after being jump started the jeep would run fine, but as soon as I disconected from the other car my jeep would start to spudder and then die. after replacing the alt, the jeep ran fine for about 15 min. until the voltage started to drop then I turned off the jeep so that I dont burn out another one.
 
Yeah, probably not (the corrosion issue, I mean.)

The FSM does say there is OBD support through the PCM for this system. Did you have a check gages light come on? Or have you checked for codes? Just a thought. Another thought-maybe try having the alternator bench tested somewhere just to eliminate it as the problem.
I don't see any specs for testing PCM outputs to the alternator for voltage regulation, other than the general description. I wonder if you put a meter on those two field circuit connections at the alternator while it's running will reveal whether the PCM is sending a signal out to the alternator? That way you can at least tell that the voltage regulator circuits in the PCM are doing something.
 
Cool. I should have said this before as an fyi, but I got mine off the MAC Tools truck for around $55. It's a MAC ET50 little handheld scanner, 'bout the size of a pocket calculator. Don't know if you have access to a MAC truck, but it was a pretty good deal. I love mine.
 
So the alternator is not bad, I had it bench tested yesterday. The only code I read was po118 which is high voltage on the temp sensor, which was fixed by tightening the connection. Any ideas on where to look next?
 
Uh have you tested the battery? Load-tested, etc? Never saw any mention of that. Sputtering then dying when removing the jumper cables can point to that; things start to get weird when the battery starts to put out less than 9 volts (computer can't function).

Other than that, refresh your grounds. If the cables look shitty, replace them. Don't just throw multiple alternators at the problem without testing simple things first.
 
Don't downplay the advice of others...Check...then re-check that you have good battery and good battery connections. I mean, mae sure they're clean and tight. A poor ground will cause all sorts of problems, and is simple/cheap to fix!
 
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