Strange Occasional Running/Charging Issue

A friend of mine has a 97 sport, 2wd, 4.0, auto, most power options. Completely stock, 210K very well taken care of that has developed some strange issues latey... on an hour trip, 15 minutes away from home the volt gauge dropped when I was driving, I turned off everything electrical I could and made it home barley. I believe it was the internal regulator because a few days later when I picked it up to see what was wrong the gauge showed it was charging normally ~14v, the next time I started it it only read 12v. I changed the alternator and it had a new battery a few months ago. Good for a couple days. Now less than a week later she called and said it has been shuddering and acting like it wants to stall and the volt gauge rises and falls at traffic lights and when driving. But it only happens randomly and sometimes it drives perfectly. I'm thinking its a loose connection somewhere or possibly a bad or going bad relay. Just wondering if this has happened to anyone else, I'm hoping its just a relay or loose connection. Going to check connections etc. tomorrow. Thanks.

Ok, the 91+ have Nippon Denso alternators, and they are externally regulated by the PCM, the powertrain control module.

First, put a voltmeter on the battery terminals and check the static voltage--looking for about 12.5 volts. Then check the voltage with the engine running--should be about 13.5~14.5 volts.

Try cleaning all the cables and renew all the grounds. Pull the connector off the PCM and clean the contacts, use a little dielectric grease on them.

You said you changed the alternator--new, reman, salvage yard?

Forgot about the alternator being controlled by the PCM, battery cables were cleaned, going to check all grounds tomorrow and volt test. I replaced with a NAPA reman (not the cheapest one they sold but a step or 2 above).

Ok, post up what you find.

Also, there are two maxi fuses in the PDC, I think they are both 60 amps, check them too.

Ok, cleaned the battery terminals really good, checked all relays, grounds, wiggled around all the harnesses in the engine bay to check for loose connections or broken wires and nothing changes the issue. It stumbles like it wants to stall and isnt charging on first cold start up until it begins to warm up, once it has warmed up it runs smooth and charges as it should. When it is cold and stumbling it goes back and forth between charging and not. I had another PCM from a 97 or 98 in my parts stash that was on a similarly optioned XJ and it didnt help the issue and ran the same. The Duralast battery is around 2-3 months old, it's not throwing the check engine light, and it doesnt seem to be the alternator as it charges as it should when it warms up even with all electricals on. What else could be the problem???

Well, pull the alternator and take a look the brushes/armature.

Yeah I figured that was going to be the next step. I'll probably pull it tomorrow and check it out, possibly exchange it to see if it may have been a bad one. Aftermarket parts these days seem to get worse and worse, if she could afford a new original I would've made her buy it instead of going through this. Thanks.

hoodride said:

Yeah I figured that was going to be the next step. I'll probably pull it tomorrow and check it out, possibly exchange it to see if it may have been a bad one. Aftermarket parts these days seem to get worse and worse, if she could afford a new original I would've made her buy it instead of going through this. Thanks.

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Ok, keep us posted on how it goes.

Good luck.

Will do, do you or anyone else know if there is a way to bench test an alternator to show if it's good? I work on old Volkswagens and you can hook up the old generators to a battery and if they attempt to spin slightly in the reverse direction they are usually good ones. If not I'll take it to Autozone and get them to test it as our NAPA doesn't.

There are some tests you can do with a multimeter, but I would check the yellow pages and see if you have an electric motor/alternator shop in town and have them check it.

EDIT: link to pdf by Fluke using a multimeter http://assets.fluke.com/appnotes/automotive/beatbook.pdf

Thanks for the info on the multimeter today. Turned out to be a bad alternator, exchanged it and so far everything is running and charging good. The alternator I removed made a clicking sound when spun that it didnt have before I put it in so who knows what went wrong with it. Thanks for the help.

Glad you got it!