Help! 99 Jeep Cherokee charging problem

jbkelly0211

jbkelly0211

Well-Known Member
Joined
Jul 20, 2010
Location
Charlotte
This problem is driving me crazy. It all started a 2 weeks ago when I blew the lower coolant hose while driving. The jeep got hot as hell before i realized it had blown. I put a new hose on it, and refilled coolant. Later that day I was driving and my volt meter dropped to 9 volts, after driving for about 10 minutes. I limped it home and once parked i removed the battery cable and it cut off, So i know it was making no power. I cranked it again put volt meter on alternator and it is making 0 volts. After sitting for about 2 hours I went back out and cranked it, it was charging fine. I took it and had alternator tested and it was fine. Battery is less than 6 months old. For a week or so it drove fine, then I began to notice the pattern: Drive for 5min or less, no problems. Between 5 and 10 min of driving the volt meter begains to wobble between 14 and 9 volts. After 10-12 minutes of driving it quits charging altogether. If i let it cool off, it will start the sequence all over again. This sequence has happened to me 5 or 6 times now this past week. I put a new alternator on it saturday, same thing happened so i returned the new alternator. I put new battery terminals on and cleaned/dielectic greased all connections. I feel like somthing heat related is causing the charging to stop, but battery stays cool. What could this possibly be? I am out of ideas.
 
Stopped by a local shop this afternoon and he thinks its the PCM, but he made that decision based on what I told him, he didnt test anything.
 
Another update, I just let it sit for a few hours, cranked it, charging great 13.72 volts. Pulled out of the driveway and stood on it to 70mph and the volt meter immediately dropped to 9. Tested alternator, it was putting out 0 volts. I unplugged the harness off the back and it was still 0 on one wire and 12.54 on the other. Which is what it usually is. Should I get another alternator and try it?
 
How many miles on the Alternator? I had a similar problem with my '98, ended up that the brushes were worn and sometimes they would touch and sometimes not.
 
I know what would fix it, a 4.6L stroker! But otherwise I'd try the PCM. Thats what my thoughts keep leading to. Sounds more like a voltage regulation issue than a voltage production issue. Have you unplugged the PCM and made sure the connections are clean?
 
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