Hey guys

First time posting here but I may have a good one...

Im having issues with my charging system on my 1998 XJ, and ive just about exhausted all my ideas... I've narrowed down the issue to this: while the Jeep is idling it charges fine and everything works as expected. As I accelerate to 2000rpm with my multimeter on the generator field terminals I can see the voltage drop to 0 rapidly, stopping all charging to the battery. When i lay off the accelerator it resumes normal operation. I do hear a whine as I accelerate that could or could not be related.

I've replaced;
New alternator (tried 1 used one first)
New battery
New terminals
New ground wires
pcm (with used one)

I've checked the generator field wires from alternator to pcm and getting 0.006 ohms on both wires (dark green and DG/O)
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Only other thought is battery sensor? Or perhaps a bad ground somewhere? Any ideas how I would even find that?

 

Don't know if this the issue but "The PCM may boost the charging current at low rpm when loads are high, or reduce charging output to smooth idle quality or temporarily reduce the charging voltage to maximize engine power when *accelerating at full throttle." source: http://www.underhoodservice.com/vide...bility-issues/

Just curious, what gave you the idea to even test your voltage, were you having any issues with the jeep?

 

Thanks for the quick reply,

The reason I've done all these tests/diagnosis is when I first start the Jeep the battery sits charging at 13.5-14v but as soon as I start driving it drops down to 12v and shortly after that, it will drop down to 9-v and throw codes at me.

 

Is the belt tight maybe it's slipping

 

X2. You do say you hear a whine when you accelerate. One thing I learned about my '00. It is very sensitive as far as the belt tension goes. In my '96 I used to own the "Yeah that looks about right" method was fine. Not so much with the '00. Also with the "Yeah that looks about right" method in the '00 when I used the Krikit II to check tension I could not believe how far I was off. If I remember correctly 140 to 160 lbs for a used belt and 180 to 200 for a new. I think.

https://www.walmart.com/ip/Gates-911...ester/42730597

 

Thanks! I tensioning the belt again last night with no improvement. I also ran it af 2k rpm, and didn't notice any heat buildup at the pulley afterwards.

What really stumps me is how the voltage at the field coil goes from 12+v at idle to 0 volts at 2k. What about the battery temp sensor? Any way to bypass that for testing?