Alternator issues?

I was on my way home from work earlier today In the middle of a huge rainstorm. I got about halfway there, when my battery light came on. By the time I got home I had barely any headlights and little throttle response.
After recharging the battery and letting the jeep dry for a few hours (thinking moisture might be the problem) I start it and still have the battery light on.. Im getting 12.28 volts on my meter (at the posts) which I would assume means im not getting charge from the alternator.. Am I in the right mind of thinking or anyone have suggestions? Also, If its toast, any recomendations on a good replacement? 87 cherokee 4.0 with AC. I've never removed the serp belt, so not sure what the correct procedure is there either. Any tips would be greatly appreciated.

Thanks - Bigshooter

Well, for starters it sounds like you got water in the Alt and fried it. Alot of times when it dries it will be ok but not always. Do you hav ethe factory front skid? If not, then water can soak the alt and cause this.
I recommend that you run a factory front skid or at the very least make something aftermarket to sheild tha alt from water. I fried a brand new alt going through water before I put on a front skid.
And as far as changing the alt, its easy. Loosen the Power steering pump in order to loosen the belt. Take it off the alt only then remove the alt with the 2 bolts.

Peice of cake.

Good luck

if your alt is good then you should be able to remove the battery from the jeep with the motor running and the motor should not die. just disconnect the batt cables with the motor on and if it dies you know the alt is toast.

or you could just take it off and then take the alt to your local auto parts store. most will test them for free, however i have not had the greatest experiences with that method. i went to three different places and got conflicting reports.

hth

edit: for removing the serp belt, loosen all the nuts on the hinged braket on the power steering pump. then once all the bolts are loose, there is one that goes sideways on the right of the ps pump. that bolt controls how far out the ps pump is from the engine, thus tightening or loosening the belt. if all the proper bolts are not loosened, you WILL snap that bolt. ive done it.

stewie said:

if your alt is good then you should be able to remove the battery from the jeep with the motor running and the motor should not die. just disconnect the batt cables with the motor on and if it dies you know the alt is toast.

Click to expand...

I wish, I really wish, people would stop giving that advice.

While it used to be valid for older cars, vehicles these days are far more electronic. Disconnecting your battery with the engine and alternator running can generate a spike of a couple hundred volts - which can (and does) blow out electronic control modules.

You've got a meter - check it this way.

1) Take a voltage reading, at the battery, with the engine OFF.
2) Start vehicle
3) Take a voltage reading, at the battery, with the engine RUNNING.

The second voltage reading should be significantly higher than the first (by about two volts, generally.) The first reading is battery voltage, the second is alternator output.

Please, for the love of Gawd and all that is holy, do not pull a cable off of your battery while your engine is running! I have seen this practise blow out engine controllers in at least two cases...

5-90
Is it possible to ruin the volt regulator in the PCM by removing the neg batt cable?
I ask because one of my friends started his jeep and the starter kept on going, even when he turned the key off and took it out. So he went and took the neg cable off of the battery. Hasn't happened since. Oh ya by the was his is a 97.
Peace

5-90 said:

I wish, I really wish, people would stop giving that advice.

While it used to be valid for older cars, vehicles these days are far more electronic. Disconnecting your battery with the engine and alternator running can generate a spike of a couple hundred volts - which can (and does) blow out electronic control modules.

Click to expand...

good to know. i picked this advice up from my step-father and hes more of the old school kind of person when it comes to wrenching. I will definitly add this to my mental notes.

thanks

WHITE420XJ said:

5-90
Is it possible to ruin the volt regulator in the PCM by removing the neg batt cable?
I ask because one of my friends started his jeep and the starter kept on going, even when he turned the key off and took it out. So he went and took the neg cable off of the battery. Hasn't happened since. Oh ya by the was his is a 97.
Peace

Click to expand...

It is possible for the voltage spike generated to wreck any solid-state electronics connected to the mains. Voltage regulators have been solid-state for the last 30 years.

It's also possible to blow out clock modules, stereos, The OBD/CCD bus (if your rig is new enough,) or anything else with a solid-state component as complex as a diode - or more.

The starter motor circuit isn't solid state - there is a relay actuated by the ignition keyswitch. This relay provides power to to the start motor solenoid (another electromechanical device) which extends the starter pinion and then allows the 160+ amps into the starter motor to turn the engine. So, the starter motor circuit is entirely electromechanical - you may have had a sticking relay which was "cured" by removing the cable - but it's usually easier to just put in a new relay (and the later models used a standard DIN relay, I think. About ten bucks, tops.)

However, I'd say he got lucky. I'd have tried pulling the relay to see if that helped, but I'd not have pulled the battery cable.

Disconnecting the battery while the engine is running causes a large voltage transient to propagate through out the electrical system. With today's electronics, and the low voltages they operate at, it's quite possible to overload something, burning it out. Aside from that, the large spike created when you disconnect the battery is a sure way to burn out the diodes in the alternator, itself. So do yourself a favor--DON'T DISCONNECT YOUR BATTERY WHILE THE ENGINE IS RUNNING. In the case where the starter motor was running, with the engine off, the disconnecting the battery won't hurt anything. The key here is the motor is OFF, meaning the alternator is not turning.

So I've spent the last few hours under the hood.. Got the old alternator out, took it in for testing.. It failed every test, and even made the machine fault out to a point that the employee working didn't know how to reset it. :yelclap:

Got a new one, popped that in, tightend a few other odds and ends to stop a leak here and there. She's up and running good as new.. Next job is the rear brakes and NSS...
Thanks for the help all :flipoff:

Bigshooter