92 XJ Sport 4.0, 217K
For the life of me I cannot find the steps to test Alt charging output to battery with a meter.
After having code 41 CEL for a few days, I just installed a new Alt Another symptom was slow wipers when car was running
Didn't really drive much at nite But I suspect HDlites were dim. Volt gauge was just less than 14
Got in next morning and barely started volt gauge was buried to the left.
I figured having not changed the Alt since i got the XJ in '04 I'd better do it since that's what the code translated to anyway. At AZ had them test the old one and the new one and both passed, hmmmm -
But i treat their test machine with suspect as it really doesn't look like a good set up for testing i.e. drive belt loose and who knows how that program determines everything is working.

Putt the 3 yr old Batt on a slow charge for the afternoon while i did the replacement Alt.
Buttoned it all up and started fine no CEL !
As it sat for 15 minutes running. I gassed it and saw no real volt gauge movement. Then let it idle with hdlites / radio on.The volt gauge needle seemed to creep every so slowly left of 14 and at one point everything took a quick dip: lights dimmed and the gauge dropped a little. Voltage across batt while running 13.56 and then gassing it would increase only to 13.61 then back down at idle. slowly watching the it decreas slightly 13.55 to .54. to .52 kinda settled at 13.51 Do these reading indicate anything ?

This morning started right up no CEL etc.

Your thoughts ??

 

Bad voltage regulator.

 

i understand, if correct, that the V reg is within the computer module ?
i.e 92 XJ

 

i would lean more towards a connection issue than a voltage regulator..

take your dvom at your battery terminal, put on dc, put on posts and take readings at idle and off idle.

check all your connections before the computer.

 

They look pretty normal to me. Check the battery voltage with the engine off, check again with the engine running. Should be higher with the engine running, indicating your alternator/regulator is working.
Then with the engine still running, load it down by turning on the high beams and heater blower. Voltage should still be above the reading taken with the engine off. Good?

The quick dip- did your electric radiator fan kick in? That'd be my guess.
The dashboard voltmeter is notoriously suspect. Don't trust it to tell you much.
Might be a good time to go through all your battery/charging circuit wiring, cleaning and replacing as necessary. Hit all the ground points too, esp, battery to block and frame.

 

Good one, the elect radiator fan ! Probably did kick in since it had been running for 20 mins or so and was fairly warm here yesterday !
Will take the readings in a bit . I had left it outside all day today now bout 45 degrees out. Started right up gauge was just above 14 and running fine !
I do take a grain or 3 of salt when it comes to factory gauges Just like to include all info for your guys benefit and a good reply back.

Will update later

 

While you're at it, might just wanna check your alternator. And like Radi mentioned, that short 'fall' in the voltage on the gauge occurs when your fan kicks on, or cycles.

Anyway, here two links for testing your alternator really simple, at home, with a digital meter. First link is most helpful.

http://www.ericthecarguy.com/electri...id=FTGz0PKIl84

http://www.ericthecarguy.com/electri...id=ZuumBVz6WOM

 

I've had batteries do some really goofy stuff in the past, they would show good charge/bad charge.. running and not back and forth, last one I had was on my wife's quest about 5yrs ago... everything checked out okay and I was duped after hours of messing with this thing... the next day we was going to take it to the dealer, I decided to try my truck battery in there tempo... it seemed to run fine, I went to the parts store and bought a new battery and sure enough that was the problem...

boy was I happy, we thought ecu

 

Real good videos there Thanks for the links.
After it sitting all day in cool temps Just threw the meter on it:
running at idle no load 14.47v pretty strong alt charging there I think.
Engine off batt cables still connected 13.51 slowly tricking off as in .51 .50 .49
You get the picture.
w/ Batt cables disconnected bottomed out at 12.79
But as Eric Car Guy video explains sounds like Batt trickled off the charge
Forgot to do the full load test ( do tomorrow) shes all tucked away in garage

Now I see how, Will also do the neg to alt ground test tomorrow
In the video Eric mentions it, but did not do the Positive test between Alt and batt
Is this taken at the single wire connection back of Alt to the positive batt term ?
And looking for .5 to 1. v over nominal Batt voltage ?

All in all since I now have some reference voltages over the course of a day or so... so far so good ?

 

If it sits at 12.79 ballpark after a night sitting, thats fine. If the volts increase > 0.5 volts with engine on, thats indicating your alt is doing ok. Load test with all accesories on: if not dropping, I'd say your alt is doing what it should.
Pm: your rear window defog will draw a lot of amps...so you know (if you decide to put it on, dont have it on too long).
Regarding the Positive side test; I'd have to google that

 

Okay gang here is the final wrap up :

Batt after sitting all nite: 12.63v
Started right up, no load: 14.30v
With full load (hi beams radio heater wipers) 13.53v
and no load again 14.28v

Ground to alt case test came up .06v ....which as described in Eric Car Guy video is under the .1 -.2v indicator of bad grounding.
Then 0.06v is a good reading.
So i think I'm all set. with much thanks to you guys replies !

Now I gotta pull a trans out of my 89 Astrovan !