BigVaz

So i was heading to work today & my voltage dropped completely. When I got to work I popped the hood & disconnected the negative battery terminal & the motor instantly died.

Im not a mechanic, but im assuming its the alternator that needs replacing? Over the last couple days I was getting a faint, but weird hum out of the engine bay too? Guessing that had something to do with it too...

Any guidance is appreciated.

Thanks!

SnakeEyes814

Not certain about this, but even if the battery was dead but still providing continuity and the alternator was pumping out juice, disconnecting the battery while running would cause the vehicle to die.

BigVaz

Its starts fine & the headlights, radio etc.. all work fine for now. Thats why I figured it wasn't the battery.

Again, im no mechanic, but figured that might be the case...

SnakeEyes814

I was just wondering if even in an xj where the alternator and battery were both fine whether the vehicle would die if the battery were removed while running.... Sorry not really an answer for you.

99FreshenedCherokee

That exact same thing happened to me, I took out the alternator, took it to get tested, and came out fine.The guy then asked me if wanted to I could get the new one and if the problem didt get fixed I could return it, and nonetheless it was the alt.

99FreshenedCherokee

Also the reason your jeep died was because your alt. wasnt charging your batt and the motor was running on battery power.(very unsafe to drive like that due to voltoge drops and increments)If you run the jeep like that you also risk messing up your batt.

BigVaz

I had a friend tell me to try the disconnecting battery thing, which made sense to me...

I assumed the jeep would stay running if the Alternator was ok. So hopefully a new alternator will fix the problem...

Fingers crossed.

Thx 99FC'

99FreshenedCherokee

It should, and another good thing to do while your down there would be th big 3 upgrade, theres alot of threads on here about it.

BigVaz

Just quick searched "big 3 upgrade" & came up with nothing... Can you explain?

lynskynbnd

Back before cars had computers, disconecting the battery was an acceptable way to check an alternator or generator(on even older cars).

The alternator will produce enough Current to keep the car running.

HOWEVER!!
On a diconnecting/reconnecting the battery with the engine running will create a voltage spike that can kill a computer.

Use a multimeter.

BigVaz

It started right back up after I re-connected the battery, so I think the computer is ok. (hopefully) lol

99FreshenedCherokee

My bad

Theres alot more let me pullm out

Jeroen

If I were you I wouldn't just start swapping out yet. Go to your local Autozone or similar and get them to run a (free) diagnostic on your battery/alternator. Based on their findings decide what needs swapping if at all.
Jeroen

xjhawk

when you disconnect the battery while the jeep is running, is causes the alt. case to ground the electricity being produced. This can cause burning out a good working alt. ALways try to use a mulitmeter to test volts. A bad ground connection can cause an alt. not to charge, make sure all ground look good before spending money.

99FreshenedCherokee

Heres a good vid I used to setup my rig.