Long story short, I went off-roading today and after I ran through a
mud pit (wasn't very deep, maybe up to the wheel hubs) and I think I
killed my alternator and messed up my charging system on my 97 Jeep ZJ
4.0L. My volt gauge normally sits at 14 and after running a mud pit it
was sitting at about 11 and about a mile down the trail it finaly went
below 9. I barely made it home (60 mile drive) on just the battery's
charge. I went to the local parts store and picked up an alternator and
swapped it out thinking that would solve the problem. Since my battery
was dead after the drive I borrowed the battery from my girlfriends
truck to start my truck up. Well it started up fine but the volt meter
was only sitting at 11 on a brand new battery, and as soon as I
disconnected the battery my truck would die. Finally I got my girl to
sit in the truck and give it some throttle to keep it from dieing while
I swapped the batteries, which worked but as soon as I installed mine
the volt meter dipped below 9 again and about 15 seconds later the
truck died. I cleaned out the engine bay REALLY good in order to
install the alternator and cleaned all the wiring on the alternator,
battery, the grounds and even the electrical connection to the starter.
Am I missing anything here? Is there anything else that could have
gotten messed up in the mud that would prevent the alternator from
charging? Any other ideas?

Thank you,
Fred R.

On 27 Jan 2006 18:33:01 -0800, fred1980@hotmail.com wrote:

>Long story short, I went off-roading today and after I ran through a
>mud pit (wasn't very deep, maybe up to the wheel hubs) and I think I
>killed my alternator and messed up my charging system on my 97 Jeep ZJ
>4.0L. My volt gauge normally sits at 14 and after running a mud pit it
>was sitting at about 11 and about a mile down the trail it finaly went
>below 9. I barely made it home (60 mile drive) on just the battery's
>charge. I went to the local parts store and picked up an alternator and
>swapped it out thinking that would solve the problem. Since my battery
>was dead after the drive I borrowed the battery from my girlfriends
>truck to start my truck up. Well it started up fine but the volt meter
>was only sitting at 11 on a brand new battery, and as soon as I
>disconnected the battery my truck would die. Finally I got my girl to
>sit in the truck and give it some throttle to keep it from dieing while
>I swapped the batteries, which worked but as soon as I installed mine
>the volt meter dipped below 9 again and about 15 seconds later the
>truck died.

Never, EVER, disconnect a battery with the engine running. You will
destroy the alternator, and often the computer.

>I cleaned out the engine bay REALLY good in order to
>install the alternator and cleaned all the wiring on the alternator,
>battery, the grounds and even the electrical connection to the starter.
> Am I missing anything here? Is there anything else that could have
>gotten messed up in the mud that would prevent the alternator from
>charging? Any other ideas?

To charge a battery you need (ideally) 13.8 volts, but 13.5 to 14.5
works. Less than 13.5 and it is not charging (which I think you
realized, but I wanted to clarify that). So you dropped in a new
alternator, new (or charged) battery, and it still only read 11volts?
Then it wasn't charging. No need to go further.


It is not recommended to use an alternator to charge a compoletely
dead battery. It is hard on both the battery and the alternator (I've
seen alternators damaged when they tried to charge totally deead
batteries...)

Consider that the new alternator was defective from the get go.
Replace it. Charge your battery with a regular charger (10 amps over
night will generally do the trick and won't cook the battery). Put in
the alternator and battery and start. Still < 13.5 volts? If yes use a
known accurate volt meter and check the battery voltage at teh battery
just to confirm the vehicle's volt meter (which often is not terribly
accurate...)

Once that is done, and it still is not charging check: fuses, and
voltages to teh alternator.

>
>Thank you,
>Fred R.

The fan belt likely just got polished up so it doesn't grab the
alternator pulley. This happens all the time to my Jeep when i take
them out to play in the mud. Mud = liquid sandpaper.

Now that you ran it open voltage with no battery, the computer is very
likely fried as well as the new alternator likely puked out it's
electronics.

Well, when my old roommate ran his with no battery thanks to an
incompetent shop that forgot to tighten the cables so one fell off, he
killed the new alternator, the computer, the ignition module and his
stereo. Hopefully you are luckier....

My test for a polished up belt is to take a cold off engine and try to
hand slip the alternator pulley. If I can hand slip it, it will not
grab good enough under load to charge. The alternator takes a few HP to
spin up under load.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

fred1980@hotmail.com wrote:
>
> Long story short, I went off-roading today and after I ran through a
> mud pit (wasn't very deep, maybe up to the wheel hubs) and I think I
> killed my alternator and messed up my charging system on my 97 Jeep ZJ
> 4.0L. My volt gauge normally sits at 14 and after running a mud pit it
> was sitting at about 11 and about a mile down the trail it finaly went
> below 9. I barely made it home (60 mile drive) on just the battery's
> charge. I went to the local parts store and picked up an alternator and
> swapped it out thinking that would solve the problem. Since my battery
> was dead after the drive I borrowed the battery from my girlfriends
> truck to start my truck up. Well it started up fine but the volt meter
> was only sitting at 11 on a brand new battery, and as soon as I
> disconnected the battery my truck would die. Finally I got my girl to
> sit in the truck and give it some throttle to keep it from dieing while
> I swapped the batteries, which worked but as soon as I installed mine
> the volt meter dipped below 9 again and about 15 seconds later the
> truck died. I cleaned out the engine bay REALLY good in order to
> install the alternator and cleaned all the wiring on the alternator,
> battery, the grounds and even the electrical connection to the starter.
> Am I missing anything here? Is there anything else that could have
> gotten messed up in the mud that would prevent the alternator from
> charging? Any other ideas?
>
> Thank you,
> Fred R.