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Alternator/wiring issues

srmitchell

srmitchell

NAXJA Forum User
Location
Mckinleyville (Humboldt) CA
Driving to school today, the jeep was running fine, when all of a sudden, the volt gauge dropped to 9 (red zone) and the check gauges light came on.

2001 4.0L, 158k miles, stock alternator, new battery.

It was running totally fine, besides the gauge. I took it to kragen and used the battery/charging system tester.

I tested the battery, it has 100% state of health, but it was at 50% charge. Once started, it said there was a PROBLEM, and that the diode ripple wasn't detected.

I looked at all the wiring, and decided to upgrade it, because a lot of it looked to be in bad shape. I changed both battery cables and... I swapped the alternator to power distribution wire to a 4 gauge standard wire.

I just realized that the stock one is a fuseable link... So I guess I shouldnt have changed that out? Could it be that the stock one blew a fuse?

What to do next? I started the jeep up, and it seems to be charging, (volts near 14) but the check engine light is on.

Any suggestions? Thanks.

Sean
 
Weird electrical stuff going on with mine too. I'll have to start my own thread though. As for the alternator to PDC cable, yes, you should have a fuse in there. Especially if there's a chance that your factory fusible link blew. This is where people commonly use an ANL fuse in place of the factory fusible link. You can see where I squeezed mine in right next to the base of the hood prop:



As for why your Jeep did what it did, I don't know. Blown fusible link would explain why it wasn't charging. If you didn't toss it out, cut it open and look to see if it got fried.
 
I can't find good info anywhere about how big that fuse needs to be.
Where can you buy one of those anl fues?

I also just went outside and started it up, the voltage is below where it should be, and it seemed to get worse with lights/the fan on.
 
your symptoms are the classic "bad diode trio" problem:

-alternator makes electricity when it is running
-sometimes makes 14V, sometimes 10V
-battery is good, but low
-charging circuit shows no diode pattern

I would pull the alternator and have it bench tested (divorced from the vehicle) and confirm that the diode/diodes have failed soon. An un-rectified alternator is pushing A.C. current through a sensitive electrical system designed for D.C. current. Batteries, ECUs, and other electronics don't like that very much:(

ANL fuse should be slightly higher than total alternator output (example- 100amp alternator should have about a 110-120amp fuse)
 
Sounds good. I'll pull it out and get it tested at oreillys. I did that for people daily when I worked there.
 
I just did some digging in the 2001 fsm.

There is NO fusible link listed in the alternator to pdc wire.

That wire runs straight to the fuse #5, with is a 40 amp maxi in the pdc that goes to the cooling fan. I'll check all my fuses when I get home.
 
im sry did i read your "lowered 2001 xj on 28's" signature thing right? i think it was supposed to say what the hell was i thinking i'm a dumbshit. lowering a cherokee is just XXXXed up dude.
 
master turner said:
im sry did i read your "lowered 2001 xj on 28's" signature thing right? i think it was supposed to say what the hell was i thinking i'm a dumbshit. lowering a cherokee is just XXXXed up dude.
Click to expand...
:roflmao:

hint: don't say dumb things and people can't quote you saying dumb things.

OP - Shorty's advice is very good (go figure, he deals with this on a daily basis!) Follow it, if you still can't find anything, check to make sure your alt field coil is being powered properly when it fails. Could be tough to catch, this is where I wish I had a 12VDC powered oscilloscope I could take along in the passenger seat.
 
master turner said:
im sry did i read your "lowered 2001 xj on 28's" signature thing right? i think it was supposed to say what the hell was i thinking i'm a dumbshit. lowering a cherokee is just XXXXed up dude.
Click to expand...

You might want to refrain from insulting club members if you'd like to remain around this forum.
 
The check engine light was because it didn't properly re-install the battery temp sensor.

I checked/cleaned about 4 grounds in the engine bay, yet it's still not charging.

I'll pull the alt tomorrow and get it tested.
 
srmitchell said:
I just did some digging in the 2001 fsm.

There is NO fusible link listed in the alternator to pdc wire.

That wire runs straight to the fuse #5, with is a 40 amp maxi in the pdc that goes to the cooling fan. I'll check all my fuses when I get home.
Click to expand...

I just checked my '99 FSM (8W-20-2) and it definitely shows a fusible link in there. 6 gauge BK/WT wire from the alternator, running to the 10 gauge DG fusible link, connected to the PDC. Wonder why they would have changed that for the 2001? What's protecting your electrical system from a surge originating from the alternator? I don't think a 40 amp maxi is the answer seeing as your alternator is probably capable of at least ~120 amps. Interesting...
 
Funky. I've noticed some other issues with my 01 FSM so I suspect it's inaccurate...

Is there a green section in the wire from the alternator to the PDC lug? It is probably at the PDC end.
 
Got this guy tested
fcb8a9dc.jpg


It's toast. I ordered new one at kragen (no one stocks it).
It arrived today. The box said the correct 13906, but the alternator was a 15906, clearly labeled! some one messed up, and Im pissed. This is my only ride!

I wont get the right part until tuesday. Such a bummer.
 
I tried looking up that alternator online but there were no specifications. You sticking with stock amperage, or getting something with more output?
 
srmitchell said:
Got this guy tested
It's toast. I ordered new one at kragen (no one stocks it).
It arrived today. The box said the correct 13906, but the alternator was a 15906, clearly labeled! some one messed up, and Im pissed. This is my only ride!

I wont get the right part until tuesday. Such a bummer.
Click to expand...

good to see you've found the problem-- sucks that nobody keeps it on hand-- I just checked locally and all three of my closest stores had it on the shelf:roll:
 
Isn't there an alternator rebuilder in your area?? That would be (and was) my first choice. You know then that you are getting good quality parts and they are cheaper than buying a "new" rebuilt alt with questionable parts.
Just my 2 cents.
 
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