oywa78

Hey all, I'm a newbie here and I need a hand right quick if you can. I'm sorry if this is long, but surprisingly I've found very little help on the internet on this, so I want to be detailed. I have a 1994 Cherokee (XJ) 4.0 and I noticed my charging meter dipping down to just above the red, but only on wet days and only when I come to a stop. It shoots way back up when I accelerate. The battery and alternator both show some age, but a bench test at Autozone showed both to be good. For some damn reason, the manufacturer decided to put the alternator down at the bottom (under the AC). Since this only happened whenever I drove on rainy days, I assumed some water was splashing up onto the alternator, causing it to malfunction, despite me having a skid plate that seems to cover it completely from the bottom. The other day it was raining and I started it up to go to work and I noticed the meter dipped to just above the red, but I had just started the damn thing, hadn't even driven it yet that day, so nothing was wet yet under there. That really confused me. A few months ago I removed that black rubbery mat from underneath that blocks the mud, to change the rear main seal (that was a fun one). I couldn't figure out how to weave it into the steering components to get it back on, so I left it off and now my serpentine belt is probably getting a little wet, because it squeals occasionally now. Could be the belt slipping, causing the alternators performance to slip, right? Well this has been going on for almost a year now and it's getting annoying. Every time it's wet out and I come to a red light (it dips down at idle) I have to keep shutting off my accessories to take the load off of the alternator. Does this ring a bell to any of you? I appreciate any feedback you can offer me.

oywa78

The main point here is that it only does it on wet days, not only when driving, but even after it's sat all night. The only constant so far is moisture being in the air. What exactly can mere moist air affect?

nujeepguy

did you read the batt volts with a volt meter? could be dash meter circuits?

DEN1956

hi sorry to hear of your problem,but i can tell you this..i have a 1997 face-lift 4.0ltr xj..and just a couple of weeks ago..upon starting the engine...i had the 'check gauges' light come on..and i noticed that the voltage meter needle was not showing a charge..so i took off the the alternator (mine is on top of the engine)..and i removed the back cover plate to get the the carbon brushes..they was very worn..i bought a new brush box..and fitted it..only £5.25 UK currency..i fitted the new brush box and refitted the alternator and all is now well...so it maybe worth your while to remove your alternator and check the carbon brushes..and replace them if there worn...good luck to you.

freegdr

ECM controls charging. Are its connection clean and tight there ?

jpz

I would start with the belt tension. It's simple, and will cost you nothing more than time. My Jeep is the first vehicle I have owned that required adjustment to the belt tension (all other vehicles had auto adjusters). it took some time, but I finally got my belt tension correct. During my learning process, my belt would sometimes squeal and the batter gauge would sometimes dip down. Not quite a low as you describe, but still it's free for you to check and adjust the belt tension so start there.

tiger02

I had the same issue as JPZ with a loose belt causing my voltage to read low or not at all. This happened on cold wet mornings and then periodically until it got warm. The reason I suspected the belt tension was that I could see the belt running and turning the water pump and idler pulley, but shining a flashlight showed the alternator pulley not turning. The belt was just sliding over it. New belt from Amazon and tensioned tight solved the issue. My belt never squealed when this happened.

BlueRidgeMark

Agreed, though I doubt that's the source of your problem. But it's FREE, not difficult, and just oughta be done!

Next, check your grounds. All of them. Clean them down to shiny metal, coat with dielectric grease, and re-attach.

While you're doing that, inspect all of your wires connecting the alternator and the battery. Look for corrosion seeping up under the jacket. Replace as needed.

Finally, just because it bench tests well, doesn't mean your alternator is okay. Wet weather may just be too much for it.

oywa78

Sorry, I'm late responding here. I will check back again tomorrow. I did tighten the serpentine belt a bit and that didn't work. I will track down the ECM and check the connections there. As for the bushings on the alternator, the alternator and the battery are both obviously very old. The battery has a slight bulge on one side and the bracket holding the battery in has ricotta cheese looking stuff all over and the insulating layer of the bracket has been eaten away. I'm going to replace both of these just for the peace of knowing they are both fresh with new lives ahead of them. I'm hoping the problem goes away after that, but I'm trying to renew this thing and alternator/battery were already on my list of things to replace, even before this issue came up. I'll post back after I replace them and let you know if the problem goes away. Thanks for the help everyone!

BlueRidgeMark

A bulged battery? Time to replace it. Battery explosions are not fun. Been there, done that.

Might want to consider replacing your battery cables, then. There are a couple of guys on here who sell kits, and they are well reviewed. I think they both offer larger cables, like 4 gauge. That's a nice upgrade. Anything bigger is just a waste of copper. Don't buy the big cable for the head-to-firewall braid. Just replace it with a similar generic braid cable from your local auto supply. It doesn't carry any appreciable current, and you don't want it to.

Or you can roll your own with cables from www.bestboatwire.com, and battery terminals from .

DFlintstone

Nerd attack! PCM, (power-train control module), for 91-01 HO's, (OBD I n' II). 87-90 Renix, ECU, electronic control unit.
If I myself had any concern of what the dash gauge said I'd put a real meter right on the battery, (like suggested). When I have scraped my terminals and clamps shiny bright I slather all in regular bearing grease, then install. Or you can get packets of Ox-guard at the auto parts. We don't want battery gasses getting into the connection.