OK, I did quite a bit of searching on this forum, with some contradictory information. I also heard contradictory information from other sources as well.

Here's the scenario:
- 2000 XJ 2WD 4.0/Automatic w/156k miles
- PO installed a new battery at the end of June (guess he thought that would solve this problem)
- Symptom: When you start it up, the starter cranks fairly slow, but eventually cranks enough to start. This morning, it just about didn't start at all, but again, finally did.
- Symptom: With engine running, in Park, at Idle, with every possible accessory on (A/C, Radio, Rear Defroster, Wipers, Blower Fan, Fog Lamps), the headlamps appear dim.

I suspected this was a bad Alternator, especially since the battery was replaced just over 3 months ago, but I've been fooled by starters with Dead Shorts in them before.
I brought the truck to a very competent local Auto Electric shop today, and had them hook up their machine to do an on-vehicle test of the charging system, and load-test the battery.

The battery test was fine.

When we started the truck, and turned on every possible accessory, in Park, at Idle, it was putting out 60-70 Amps, but only about 12.6 Volts. Again, knowing just enough on older vehicles, I would suspect a Voltage Regulator, but the guy at the shop thought this one was not in the Alternator, but in the ECU, so it could also be the ECU. He said the only way to be sure, was to yank the Alternator & bring it to him, and let him test it on the bench, and possibly open it up.

As to the ECU containing the Voltage Regulator, I've heard that on other vehicles, and read it on this site, but I also read on this site (and read about other vehicles) that it's actually *inside the Alternator*, and is simply controlled by the ECU.

I believe if the Voltage Regulator was built into the ECU, and it wasn't functioning properly, it would be throwing a CEL, or at least have a Code stored. The truck has had at least 500 miles put on it since we bought it without disconnecting the battery, and there is no CEL, and no Codes stored. I had the local Advance check for codes to confirm today, and none were present.

So my main question is regarding the relationship of the ECU to the Alternator & Voltage Regulator. Is it in fact an Internal Voltage Regulator in the Alternator, and simply controlled by the ECU? I also read that there's a way to confirm that the issue isn't with the ECU controlling the Voltage Regulator, but the Alternator/Voltage Regulator itself.

And the obvious and main question...do all these things point to marginally working, weak Alternator, which should be pulled and gone through by a local Auto Electric shop (not replaced by a likely DOA reman unit)?

Thanks!

 

Voltage regulator should be a part of the alternator. Simply start your jeep with no accessories on and check voltage. At the battery it should be around 14v. If you don't have 13.5v-14+v at the battery get under the jeep and put the positive side of the multimeter on the hot wire at the alternator and obviously the black on ground. If you have 12 Volts it's a bad alternator. If you have 14 or so volts at the alternator, more than likely the fusible link or fuse for the alt is bad.

 

the alternator would have nothing to do with the slow crank. starting and charging are two seperate systems with a few shared componants. the alternator wont start really charging untill the key returns to the run position after completing start.

the regulator is in the ECM (brain), the ecm controls the alternator in newer jeeps (95+?) In older jeep like the renix the regulator was bolted to the alternator.

It sounds like the alternator is working properly, loaded its putting out a good amount of amperage, voltage may be a little low but 12+ loaded is normal as long as it holds 12+ with load. the more items you tax the chargin system with the "dimmer" the light will get, It is more noticeable at idle as well, if you rev it to about 1200 rpm I bet the light s would regain brightness as the alternator can now output the proper amperage to keep up with the demand.

My guess to your starting issue is the starter has a high amount of draw and the starter motor is worn causing high resistance and slow cranking. needs to be checked for sure.

 

I would tend to agree.../\ /\. Idling at 12.6 with everything on says she's putten out. (charged/rested at room temp 12.7 is the magic #). That it met the max system demand at idle, is like having one hand tied behind its back.

If it cranks slow with the battery up and a jump, you'd know to start checking your batt. cable connections and/or your starter. (you know a bad connection will get warm, or hot).I just got a free replacement starter from Napa cause of the lifetime warranty. (was only the solenoid though!)

 

OK, this is now officially one of those things that seriously irritates me...

I drove it around town all day yesterday, including stopping to have it tested at the Auto Electric place. Multiple starts & restarts, and while they all sound mildly slow to me, it actually did start every time.

Keep in mind that when I had it tested at the shop, with everything on the planet running, it showed 12.6V & about 60-70A at idle, both rising with an increase in RPM. During the test, the headlamps were visibly dim.

Fast-forward to this morning....I go out with my Multi Meter, and before I do anything, I pop the hood to check the resting Voltage at the battery.

12.6 Volts

I start it up, turn everything on, and test it again while it's running at the battery, and now it's showing about 13.6-14.2 Volts, which it should. Also, the headlamps were not dim, like they were when I had the guy testing it yesterday, and he only showed it at 12.6V at idle.

I scratched my head and said 'Hmmm...' for a minute or two, because that's exactly the opposite it did during the shop test yesterday.

So I shut it off, then immediately go to restart it. This time it's clearly cranking slower. I shut it off again, restarted, and even slower. I did this about 3-4 times, and finally it wouldn't even crank.

So I let it sit a minute or two, hit the key, and it starts just fine...not even slowly! This was exactly what happened when my GF tried to start it yesterday morning.

I tried to replicate it, by starting, shutting it off & restarting it maybe 15 times in a 2 minute span. Never happened again, and in fact it would start so quickly, that when I would just 'bump' the key, it would start and run.

So here's where my mind is going now...

- Marginally Failing Starter/Solenoid. Perhaps a bad spot or two in the brushes/contacts. - But then why the dim headlamps/marginal test results yesterday?
- Bad Ground and/or other connection. - Seems that these trucks are sensitive to either.

After an eextensive Search in the forums, I also found this, which sounds familiar:
https://www.cherokeeforum.com/f2/jee...ns-over-46949/

I almost started to think that perhaps the battery has a bad cell in it, which is what it hit when the problem manifested itself, but the battery was new on June 24, and resting Voltage checks out.

I can see this thing is going to have me chasing it and going nuts real quick-like....

 

I was tricked a little once. Slow crank/no crank. Was alone, so I couldn't hit it while the key was turned like normal. I needed to smack it with a hammer THEN go get in and try it. Worked. Down the road it turned out It was the battery connection on the starter, (not sticking brushes or the solenoid). Jostled it enough to make contact. (caught that connection hot and sizzling later)
Since it would act up even while jumped to a known good other car I could rule out Batt. issues.

/\.......I don't think your headlights should be dim at 12.6........./\
..........connections, especially grounds. That braided from the back of the engine to the firewall gets allot of responsibility!