Is it a bad alternator or something worse?
 

About a month ago I blew the headgasket on my 99 Jeep Cherokee with a 4.0 L inline 6 cyl engine. I took my engine apart and found out I had a crack in the head. Well I got that fixed, replaced all the gaskets, got a new thermostat, temperature sensor, water pump, radiator, and hoses and got my baby running again. Woohoo!!!

I drove it for about a week and put about 250 miles on it when the voltmeter bottomed out (at 9 volts but I'm assuming it was lower). My first thought was that the alternator was bad and pressed on because if I had a dead battery and stopped I wouldn't get the car started again. Well after about 3 miles, I started to hear some clunking and decided to stop to take a look. Everything looked fine (belt was intact and taut) so i decided to press on. After a rough start (I think the battery was low), I got it started and continued on down the road. The voltmeter read voltage for a moment and then bottomed out again. About 2 miles later, the temperature began to rise and I lost all power when pressing the gas and was only able to maintain about 40 mph. As I was turning off the road my engine shutoff and I coasted to a disappointing stop. As a friend of mine was towing me home I was able to listen to the radio and keep the flashers on with the voltmeter reading 12V.

A coworker of mine said that the alternator could be the root of all of my problems if the fuel pump and temperature sensor are powered by the alternator. I replaced the battery in November (~6 months ago) so I don't think it is that. Has anyone had this problem before or have any ideas?

Thanks,
99greencherokee

Without a good running alternator you're battery will get drained, so I say charge the battery and if it'll crank run over to the auto parts store and have them check your alternator.

could be alt. the computers need at least 9 volts, or something like that, to run the jeep . if the alt. is junk and your battery is way low, the computers start to fail to function.

Its prolly the alternator. I just recently went through these same symptoms and mine was the alt.
Replaced it last friday~ no more issues at all. Get a good one... cheap ones are just that~ cheap.
Good luck!
:)

Clean the battery cables/terminals first!

good suggestion, but i highly doubt that his problems lie in dirty battery cables.

XX2^^ Clean battery connectors and posts, put battery on a good charger (overnite) install new alt. (clean and di-electric grease all connections, except the battery posts ;)

Battery cables can be "good" until they are disturbed (aka removed for battery replacement) Clean those bad boys, Tighten em down and make sure they are not able to twist at all. Even a slightly loose cable can spell trouble.

I've posted a writeup in OEM tech on testing primarily electrical - works on any vehicle, you just need a voltmeter. Search it up and run through it - it will be a very instructive half-hour for you.

IP gages should not be trusted for diagnostic use, the very first thing you should do when you suspect a problem is confirm that there is a problem...

5-90, I thought to try and find this write up, but whats it called? cant find electical testing stuff in either Tech or Write up's.

It's in whatever is the General tech section here (I've posted the same thing on at least a half-dozen boards, because I was tired of answering the questions.) Keywords are alternator, starter, battery - they're in the title.

Finally got around to it and found your check. Everything checked out good. Voltage was at just over 12 when car was off and just under 14 while running during all of the checks. I even took the alternator to the shop and had them hook it up to their machine and it passed...twice!! 13 years old and the alternator is still going...that seems pretty good to me.

Anyway, when the car was running I noticed antifreeze dripping from my bottom hose. I repositioned and tightened the hose clamp and put quite a bit of fluid into the radiator. I let the car run for over half an hour and no overheating and nothing with the voltage.

Was it just coincidence that the voltmeter had a false reading and I happened to have leaked all (or enough) of my antifreeze to overheat at the same time or are they definitely related? Maybe the heat from the hot day and the hotter than normal engine really did cause the alternator to fail but when it cooled it was passable. I'm going to start upping the mileage again and see if anything goes bad on me. Hopefully I won't be too far from home if things go awry. Lol

I just picked up a 96 Cherokee 4.0 L inline 6 cyl engine at an auction and have a similar question. The Cherokee started with a jump, I replaced the battery and tested the alternator which was bad (I knew that when I bought it). I got the Jeep home, but when tried to get to my shop, it runs for a minute or two and chokes out. I'm hoping it's the because of the alternator and the electric fuel pump. It was a county vehicle that was rarely used (59,xxx miles) and I assume it could be fuel system related too. Any ideas?