Hello everyone!!

I've been at this for a while and cannot figure out for the life of me what is going on with my rig. I have a 2001 xj 185k on it. I have been having issues with my charging system. Every time I'd put on lights or heat or rear defrost the volts would drop below 12, but if I shut it off then it goes right up to a hair below 14 on the dash. I have a voltmeter and the dash reading lines up with what the meter says at the battery terminals. So I was concerned about this dropping volts so I brought it in to be tested at AZ, the alt and batt passed while still in the jeep, but the voltage regulator failed. So I figured it had to be the alt. I bought a high output one from eBay for $140 a while ago, it lasted three years had a bunch of humming coming out of it so I figured it was time. I bought a remanned unit from NAPA with a lifetime warranty rated for 120a. My xj is all stock, I got the high output one off ebay because it was a steal and I planned to put a winch in but my plans changed so I didn't have a need for a new high output alt. ANYWAY, I swapped in the new alt and it still dropped. I removed the battery and brought it into az and it failed so I got a new one and swapped that in. While swapping the new batt in I replaced the battery terminals and I went through and cleaned and sanded all of the grounds, except for the one at the firewall, and they all looked solid. I also cleaned the positive cables coming out of the relay box. So I just read the volts on the new battery, 12.5 or so volts cold. I fired it up with nothing on, not even the radio, and it read 14.38v. I let it run for 15mins and it dropped to 14.12v still under no load. Then I turned on everything, hot air on high, rear defroster, headlights and high beams, and radio. The more I added the more the volts dropped on the dash and the more the lights dimmed. When I step on the gas and bring it up to 2000rpm the volts rise to just above 13 with everything on but do not rise above that. I am at a loss here. The belt doesn't squeak at all when I step on the gas so I don't think the belt is too loose and, while I will clean the one remaining ground, I just don't see how that could be causing this.

Any thoughts?
Is this normal for an xj to do? Seems to be that if its an emergency situation and I'm relying on my jeep with all of the above accessories switched on the battery will die over time given that the volts it's putting out are lower than the voltage of the battery at rest. I'm trying to save some money here and I'm dreading that this could be the PCM. Any feedback would be greatly appreciated and thank you SO MUCH for reaching all of this.

 

Are the cables in good condition? The connectors and grounds can be perfectly clean but the cables can be awful underneath the rubber coating.

 

Right!! Forgot to mention I did the big 3 upgrade so all my cables are high gauge and nearly brand new, all from jeepcables.com

 

Update #1

The plastic plug for the alternator was melted right by where the prongs go in so I bought a new one and soldered it into place with no issues. All connections are clean and tight. I cleaned the 1 remaining ground (firewall to valve cover), triple-checked that everything was plugged in and attached and cleaned and then started her back up. Then I went through and turned on each accessory individually and took the reading at the battery terminals to figure out what is going on, surprisingly my volt meter on the dash was very accurate with what was happening at the battery but for specificity sake, I placed all the readings from the volt meter below so we have a definite number. If this is totally off please let me know and I can adjust how I am getting these readings. I just have a basic multimeter with two prongs that I touch to each of the battery terminals, not the posts but the terminals just in case there were any issues back at the battery.

Recap: new alt with 128amp max capacity reman from NAPA, new battery from AZ (duralast gold), big 3 upgrade completed within the last few years, all grounds cleaned and tightened, cleaned positive cables coming out of relay box, headlight switch (MasterPro from Oreilly's) replaced about 1 year ago, I bent the headlight relay to maintain having my fog lights on when my high beams come on (truth be told I'll be checking this next if no one responds), new blower motor resistor (OE performance from eBay) put in last year along with a new connector after mine melted. I also installed an inverter on a circuit breaker that has not been connected so I doubt that's it but thought you all might want that info as well. All acc turned on 1 at a time, all readings at idle just below second tick mark 500ish? bounced a bit but not much, temp just a hair below 210 never rose during testing

Cold battery, not running, no acc on
12.59v

Cold start right after startup
14.45v

XJ sat running for 15 mins, temp brought up to just under 210

15 min after start no acc
14.06v

15 min after start headlights (no high beam)
13.99v

15 min after start high heat on 4 aimed at the floor
13.89v

15 min after start two 18W led lights (at least that is how they were advertised)
13.93v

15 min after start rear defroster
13.89v

15 min after start headlights w/high beams
Jumps between 13.71-13.84v (a problem that it jumps?)

15 min after start full acc heat, headlights w/high beams, LEDs, defroster
Jumped around from 12.31-12.48v then went to 12.33 and slowly dropped .1 every 15 sec or so

Any thoughts? Is this normal for the battery to be at 12.33v and dropping when the car is at idle with all these things on? Is the voltage jumping with my high beams on a problem and how would I track that down? would more information be helpful at all?

Regardless of what happens, I'll try to continue to update you all in case some other poor soul has the same issue and I stumble upon a solution.

Thank you for anyone reading this.

 

Everything seems to be ok untill that last step.
Did you raise the rpms to about 1500 while you were doing that?

No, your battery slowly going below intial battery voltage indicates it can't keep up with demand. The voltage regulations output from the alternator is regulated by the pcm ( not entirely sure if that is different for your year). Since the battery needs to get the juice from the alternator to be able to keep up with demand, there is something not up to scratch there I'd reckon.

A healthy charging system should normally be at least 0.5 volts above battery voltage with all accessories running. But measured at 1500rpms and usually without the window defroster on. So therefor not sure what to conclude from your situation if done with defroster on and idle.

 

Thank you!!

From what I've read the voltage regulator is in the pcm for the 2001.

I will have to retest today following your guidelines (everything on but defroster and brought up to 1500rpm) and then I will post the results back here.