4x4jeepmanthing

I just got home from the trail and halfway back my check gauges light comes on and the battery gauge dives. As im getting closer to home all the lights start dying gradually which i take is my battery dying to because the alternator wouldnt be charging it?

by the time i was home the headlights were almost completely out, the clock was gone, and the dash was almost out and she was sputtering as the garage door opened.considering most probably dont make it home i am
LUCKY !!!!np

the alternator is stock 181000miles so for this reason and symptoms im under the impression it just took the kids to the pool.

My interstate battery was less than a few years old.

If this is the alternator are there any replacements i should avoid? i was thinking i would go napa as general better quality than AZ or ..... IMO/experience

99 4.0 181,000 Auto NP242
Please confirm or if there is something else i should check let me know. Its my DD and only wheels.

93XJeeper

sounds like alternator. Mine did the same thing when it went out. Any brand works. I got Autozone, been two years and it's still going strong.

99xjem

^^^ yup. Just did mine a couple weeks ago. No biggie, thank goodness, except for that bottom bolt. Whatta PITA! But just to make sure, I'd check the wiring and battery too.

Rambler65

Just replaced my alternator yesterday, similar symptoms though the first thing that happened was the speedometer going nuts. Auto Zone can be a crap shoot on quality, so I went with NAPA thinking it might be a little better. Price was actually lower than Auto Zone.

Cvail

Do you have anywhere local that can rebuild yours? Local alternator and starter shop here charges $35 and I think you end up with a better unit than a Chinese reman for one of the chain stores.

4x4jeepmanthing

Napa said the alternator is good which does make sense as my battery is being charged at interstate. Is there a fuse that could cause this?
I bought a new alternator just in case.

machinisttx

Take the alternator to a second place to be tested. It's possible that the Napa person who tested it was wrong.

Check the connector that plugs into the back of the alternator to be sure it's secure. Also be sure that the metal pins or sockets haven't pushed out of the connector. Check the rest of the wiring for obvious broken or shorted wires.

Check that the battery temperature sensor is in place/connected. It's in the bottom of the battery tray...round plug looking thing about 1.25" diameter. If the wires and connections are good, then test the sensor. At 75 to 80 degrees Fahrenheit, resistance between the two "pins" on the sensor connector(the one on the sensor) should be between 9,000 and 11,000 ohms per the factory service manual.

If your check engine light came on, there should be a code stored. What was the code?

The engine computer controls alternator output(on OBDII XJ's at least). It's possible that the control circuit in it has failed...but from my understanding when they fail voltage usually goes high.

4x4jeepmanthing

My check gauges light was on, not check engine. All wires look good and connections were secure. I replaced the alternator and had the battery recharged. So far it's running well and no check gauges light.

4x4jeepmanthing

after reading your post i search FOCO for anyone that could rebuild with no luck. most were confused and used to simply replacing the alternator.

4x4jeepmanthing

[QUOTE=machinisttx;3321553]Take the alternator to a second place to be tested. It's possible that the Napa person who tested it was wrong.

Check the connector that plugs into the back of the alternator to be sure it's secure. Also be sure that the metal pins or sockets haven't pushed out of the connector. Check the rest of the wiring for obvious broken or shorted wires.

This is exactly what i did.

I wasnt confident with the response at napa nor how the folks communicated my results. "your starter is fine" wtf.....really!!!!!! enough said there:001_
I called advanced and didnt get a good feel on the phone so i took it to AZ where they test it in front of you and I
told the guy I want to see if there is an A/C flux which the response is we see good or bad results

machinisttx

A/C flux? Not following you there. The only way to get AC current output from an automotive alternator is to remove the bridge rectifier. If/when a diode in the bridge rectifier fails, you'll either get very low DC output or more typically none at all. The alternator will also make a growling noise when the vehicle is running and it's trying to charge the battery. When they fail, they don't go back to normal operation...you have to replace the rectifier assembly or the individual failed diode(s).

You can test the bridge rectifier if you have a multimeter with a diode check function. Half of the diodes in the rectifier will be positive and the other half negative. That means half of them will show a forward voltage on the DMM with the positive lead on the diode and the negative on the heatsink, and the other half will show it with the negative lead on the diode and the positive on the heatsink. None should show voltage both ways.

4x4jeepmanthing

A/C ripple is what I ment

machinisttx

You won't see any AC ripple with parts store testers or even at an alternator/starter repair shop. If you connected it to an oscilloscope you would see some ripple(even on a "perfect" alternator, diodes aren't perfect), but I'm unaware of any parts store that has one...or would even know how to use one if they had it. The alternator test benches I've seen only test for output voltage and output current. They might test rotor current draw as well, but I've not paid enough attention to be sure.

I took an old nippondenso alt apart today...very similar to whats on the jeep and was surprised to see that everything was held in place with screws.

4x4jeepmanthing

hmmm, perhaps ill crack my original open and take a look.

That would make sense that the stores can not check A/C ripple because the guy didnt understand when i asked him to. there was an option that was supposed to give a read out for the Diodes which showed N/A, the guy said it was a bad alt. output is showing fine though so something is up with the stock alt

the new alternator is charging the battery just fine right now so im inclined to believe that my grounds are solid as well as my other wiring.

I wouldnt mind rebuilding the stock alternator if a diode can be replaced?

machinisttx

Well, I just learned something.
If the alt on the jeep is assembled the same way(I don't know for sure, I didn't check the old one on my '00 before using it as a core), then it will be fairly easy to swap the parts. Typically you would replace the entire bridge rectifier, though you can replace individual diodes in them. http://www.aspwholesale.com/rectifier-nd-p1340.html That should be the correct rectifier and http://www.aspwholesale.com/brush-ho...y-nd-p145.html is the brush holder with new brushes.

Here's a vid on repair/rebuild of several types of Denso alts.