dev_daddy

My battery died the other day. And then everytime i jumped it, it would hold a charge for about 10 minutes, but then died again. So i swapped in another battery. And the meter in my dash is pegged at about 9.5 and it isn't dead. But being held there.

Any idea?

jronald

At idle, checking at the battery, you should read better than 13 volts....provided both the battery and alternator are good. !3.7 is just about perfect.

Ron

Gee oh Dee

Check to see what the alt is putting out with a multi meter.

XJUSMC

hands down its the alt from what you are saying. If all the lines look good and fuses look good it's the alt.

to be sure put a meter on the battery while the car is running, it it is at 12.5 or lower your alt is not working.

just happened to me on thursday. gauge said 9.5 with my check gauages light on. put in a new battery (new from the store) and still at 9.5 with the check gauges light on in the dash.

reman alt at pep boys is in the 115.00 range (90 amps and if your in a bind) you can find them cheaper or with more power at autoparts wharehouse.com

I ended up with a new bat, new alt, and new belt. good luck

Fsher21

probably alt, but if it is running just run it to like autozone and they will test everything for free, and you will know exactly your problem.

Flowpro

Or Advanced Auto or O'Reillys.

als98xj

^^^ agreed. I just changed mine today. My check gauges light came on gauge dropped off but started fine. after 30-45 seconds it dropped off again. alt replacement fixed it.

dev_daddy

Thanks guys!

5-90

Having wasted a few years behind the counter at Kragen's (apparently bought out by O'Reilly's) I'm not sure about those tests.

Besides, you can't always get there.

I've posted a writeup to test your primary electrical on this and about a half-dozen other boards. You can do it in your driveway, you just need a good DMM, and the results are, I think, rather more accurate and useful than the roll-around tester that the shops use (don't even get me started on that asinine bench they use - I know how they work, because I used to fix them. Damned things are worthless for real-world testing...)

rompnXJ

or just disconnect the negative battery terminal with the engine running.
if the engine stalls, the alternator is junk.

if it does stall, verify you have B+ making it to the alternator first. if you do not have B+ at the alternator then youve got a blown fuse or a wiring problem

tjwalker

A code 41 is almost always the alternator.

Running Free

^^ that how I check mine

dev_daddy

It was the voltage regulator. Bad. Replaced alternator good to go!

5-90

DO NOT DO THIS!!!

I really wish people would stop suggesting this. This became unsafe as a test in 1974, when American automakers started doing electronic ignition controls.

Disconnecting the battery with the alternator running tends to generate HV transients, which are very much not good for the electronics that make things go. You could find out your alternator was good - but you just cooked your PCM!

(And yes, I've seen this happen. And had to fix it afterwards.)

Follow the writeup I've posted for testing primary electrical - it's totally safe for your electrical system, and will give you a better idea of what's going on anyhow.

Again, do not disconnect battery cables with the engine running! Just because I make money fixing things that break doesn't mean I want to fix things that didn't have to break, but did through user intervention...

413maxwedge

Use your volt meter check your battery with xj off you should have about 12 volts ,with xj running you should have 14-15 volts.On the back of your alt. you should find a test hole (for your year you should have this) Put a screwdriver in this and ground it to the case and nothing else, don't run your xj very long to do this just long enough to get a reading with your meter.it should be 15 volts or better, if it's lower you need a new battery if not then it's your alt.This is a test you can use, pass it on to other people if you want.