post #1 of Old 05-12-2013, 10:03 AM Thread Starter
banesterloren
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Join Date: Jul 2008
Location: nevada
Posts: 20
Can an alternator go bad slowly?

Or do they just up and quit? 1991 jeep Cherokee obd1 4.0. The jeeps been running like it's missing on one cylinder just once every couple of minutes. Like a split second stall. Last time I had these symptoms I replaced the fuel pump sending unit and in line fuel filter. Yesterday I didn't check anything on the fuel side of the jeep. I know I can check for pressure at the rail...
I just figured I'd check my codes at home since the "check engine" light came on. What I got were codes

12) Direct battery input to PCM was disconnected within the last 50 Key-on cycles.

41)An open or shorted condition in the generator field control circuit.

63)Unsuccessful attempt to write to an EEPROM location by the PCM.

...Witch leads me to believe that it is something electrical. Like the alternator. (usually this kind of stuff bothers me. Everyone always assumes it's the alternator,starter, or battery....and spends alot of money..... to find out that it really wasn't. I'm an okay troubleshooter. Good enough to know what to look for and why and how to test.)

Back on topic: So what I did yesterday was this.
Start jeep with battery.
Remove - battery lead once started
Listened to the idle and it steadied pretty good.
Looked at the voltage gauge and the needle fluttered just below 14.
Gave it gas and it took it's life away.
tried this three times.
Works fine with the battery though.
I just remember having to drive it home from work once without a battery or any other power source other than the alternator and it did fine.
So will an alternator go bad slowly? or do they just quit.
yes, I have a multi meter. I will check concoctions, grounds, resistance, maybe add a ground from battery to frame. I could also get the pressure checked at the rail if it is fuel delivery related. Thank you for reading.

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post #2 of Old 05-12-2013, 11:17 AM
buildin1XJ
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1999 XJ Cherokee 
 
Join Date: Oct 2011
Location: Knoxville
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Yes an alternator can and many times do go out slowly.
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post #3 of Old 05-12-2013, 12:52 PM Thread Starter
banesterloren
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Location: nevada
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Okay thanks. Anybody ever dealt with a 63 code.
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