I installed a new alt in jan of this year. vatozone 90 amp stock replacement. I noticed recently that my volt gauge on the dash was showing 13 volts from time to time. nothing crazy but I figured a 5 min investigation w a voltmeter couldn't hurt. I took readings off the battery. connections are clean and tight. this jeep came with a 117a alternator. this is what I found:

jeep off: 12 volts on the nose
at idle no load: 12.7ish volts
at idle brights and heater fan on: 12ish volts

revving the engine didn't change readings under load or not. sounds like junk to me.

also something I noticed. the dash gauge consistently shows 1+ volts more than what I was seeing at the battery.

thoughts?

 

Why would you put such an under rated alt in the first place since oem is 117 amps same as my 98.

 

the only power option it has is mirrors. I didn't think it would matter. it only has two 5.25" speakers. I think the alt was troublesome from the getgo but az tested it in-jeep and said it was fine 3 mo after installation. if I go back and they refuse to replace it I'll just remove it and return it. then go somewhere else and get a bigger one. if they'll take it back I'll upgrade to their 136a I think it is.

either way it's getting a bigger alt before this is said and done. I didn't know mine came w a 117a alt until after I had changed it.

 

Alternator size shouldn't make a huge difference unless you are running lots of high-current electrical stuff.

If the battery is 100% good, the alternator should be sitting at 14v or more at idle with all electrical stuff turned off. If it's under 13v, I would wager the alternator is dying.

 

Sounds like junk indeed. Even with bad cables you should see a little more action.

As far as the gauge inside, ****ty grounds for the instrument cluster will cause that.

 

Too low bud. Fully charged, a lead/acid battery rests at 12.7 at 78*. Hooked to the system it doesn't take much to drag that down a bit though. Clock, stereo memory, keyless entry. I don't think my ECU uses anything, but a PCM may well also use a tad.

Over 14 running is more like it. Over 14.8 would be a problem. Last I checked my 90 idles at 14.25 with the blower and headlights on high.

For me, low voltage is the first place a slipping belt will show up. Radi's tip, "feel the alternator pulley and see if it's warm" (the friction, if it's slipping should make it heat up).

I might also feel for heat at any connection between the alt and battery, also probe the alternator terminal it's-self and see if you have that 14 there.....

I don't have a dash gauge and wouldn't trust it if I did.

 

just to bring closure to this...my alt was charging low bc the battery temp sensor was disconnected. I bought a new sensor and plugged it back in. it now charges properly. I thought the battery temp sensor talk was dumb, I was wrong.

 

What? Tell me more....never heard of any temp sensor???

 

Yes my 99 has one as well mounted under the battery on the tray and will cause problems if not working, But I would still put a larger alt. on it to start with.

 

Lots of Chrysler vehicles have this battery temp sensor. The thing is, if you have it unplugged you SHOULD get a CEL.

 

yeah it had a cel. I ended up removing the bulb from the cluster. the sensor was unplugged all last winter. despite the difference in charging, it never failed to start or cranked slowly. however, it is obvious the battery and charging system are doing better. the lights are brighter and the damn thing cranks over like new.

 

Interesting about the battery temp. sensor. My `96 ZJ with the 5.2V8 has one. Sits under the battery in the tray. Havent checked my `96 XJ. I`ll have to pull the battery and look.

 

Some young engineer probably got a raise for thinking up that one.

We have been using lead-acid batteries for about 100 years, and now some joker needs to know the temp now, to modulate the charge rate etc Too bad someone doesn't come up with a quick & easy way to by-pass that sensor & toss it...