I've been having some electrical issues lately, including slow cranking and headlights not quite as bright as usual, so I suspected either my battery or alternator may be on the way out.

After driving back home, I just ran some voltage tests after letting it cool off for a few minutes. Here are my results using a digital multi-meter at the battery terminals. The battery cables have been cleaned and tightened recently, and I've refreshed just about all the major grounds in the last year.

Engine off: 12.4v
Engine idling with no accessories turned on: 13.6v
Idling with heavy load (high beams, blower, rear defroster, aux fan, etc.): 12.3v
Engine revved to 2,500 RPM with heavy load: 13.3v

I'll try to do a cranking test on the battery in the morning to see how far down the voltage drops. Any thoughts on my alternator test results above? As far as I know, it's the original alternator from '98.

 

Divide and conquer. Have the battery tested.

 

the alt supplies all needed curent

 

mine has shown voltages like that for the last 4 years. no slow crank or dim lights, though.

 

Upgrade your cables and refresh your grounds.

www.meanlemons.com

 

I did some load testing on the battery this morning. While cranking, it immediately dropped to 10.3v and then leveled off at 10.6v. I did it twice with the same results. That would seem to indicate the battery is OK, no?

Here's a video I shot of the voltmeter during my cranking test:


I also repeated the voltage tests I did last night with a hot engine (post #1) again this morning with a cold engine to see if the heat was impacting the alternator's performance. The result was just about same, except I got between .1v and .3v higher readings with the cold alternator. One thing I did notice when I idled the engine with all the lights and fans blasting is that the voltage dropped to 12.6v and then continued to drop over the span of 2-3 minutes to 12.0v. It's almost like the alternator wasn't keeping up with the load. I had the high beams, rear defroster, aux fan, radio, and HVAC fan on high. It would climb up to 13.4v when I revved it up a bit to 2,000 RPM or more.

I suspected that might be a factor. The cables are original I assume, but I cleaned up the grounds last year. I see there are some good cables on that website you posted, but I didn't see any instructions for 97-01 installation.

 

I had similar issues with my new to me XJ
alt was stock, original from 2001
I bought a AutoZone Gold alt for like $130.00
after that , alt ran perfect and it charged my Sears Platinum gel cell

 

Charging system is not meant to be load tested at idle when testing with something such as a vat 40 it is done at 2000 rpms here is link that may help http://www.bhsautomotive.com/uploads/2/2/5/3/2253379/_vat_40_and_electrical_testing.doc based on the 2500 rpm test you did I would say alternator isn't up to snuff however

 

you might look into the battery temp sensor. mine charged low when that dumbass sensor failed