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Old 09-20-2010, 10:50 PM   #1
Join Date: Apr 2010
Posts: 4
Question YJ Alternator Info / Upgrade

First off, Id like to thank you for all the info, help, and laughs yall give through this forum, and I'm happy to be a part of it. Unfortunately, I have seen plenty of TJ Alternator posts but, after much searching, no sufficient YJ Alternator post...

I am currently running:
- Stock Alternator
- Optima Red Top (dont know when it was installed, just bought the Jeep a few months ago and havent looked at the date on it)
- 4 Low grade fog lamps from Autozone (part #NV-120Z) I dont do night rides enough to upgrade yet.
- 8000lb Champion winch

I want to add:
- E-fan
- Air horn compressor
- Higher grade aux lights
- More speakers

Problem I am having is that every time I use my A/C, my Volts almost redline on the low end from 14volts to 11-11.5 volts. The voltage decreases as i turn up the A/C. Turning on all lights and the radio decrease the voltage as well but nowhere near as much as the A/C. Ive always considered upgrading my Alternator but never the opportunity. Now i have it.

My questions are:
Does this sound like an Alt problem?
What are the specs on the stock alt?
What are some junkyard options?
What are some professional aftermarket options?

I'd greatly appreciate the info. I know its an easy task to go have Autozone check my Alt, but either way, I'd like to upgrade it. Yall have some great information on here and some very helpful writeups.

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Old 09-21-2010, 07:11 AM   #2
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Join Date: Sep 2010
Location: Southern Maryland
Posts: 27
When you say that it drops, does it drop and stay at 11 or does it go right back up?

Depending on what motor you are running(I'm guessing 4.0) you should already have the 120amp alt. The 2.5s come with a 90amp alt.

If your looking to do a junkyard swap and go to higher than the 120 you will have to go with a alt out of a late 90s(98-99)V8 Dodge, Durango, Dakota or even a full sized van. I wanna say that the number is 4973 and that will up you to 140amp. Dodges and some Cherokees also come with a 4972 and that one is 120amp, look for ones that have power window, locks, etc..

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Old 09-21-2010, 01:09 PM   #3
Join Date: Apr 2010
Posts: 4
Sorry, yea, its a 4.0L. And it's odd, when turn the A/C on high just after a cold start, the voltmeter reads around 13v. But once ive been running for bout 1-2hrs it redlines consistantly at 11-11.5v with the A/C on full. If i turn the A/C off, it jumps up to 13v again.
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Old 09-21-2010, 04:35 PM   #4
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Join Date: Sep 2010
Location: Southern Maryland
Posts: 27
Yea sounds like your alt can't keep up with the drain.. I would have your alt tested and see if its failing or too small of an amp. Or just do the upgrade.. Doesn't sound like your getting a ground somewhere or a drain because your battery doesn't go dead after sitting. I'm not sure but could be an issue with the AC, I don't have AC so I can't tell ya..
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Old 09-21-2010, 10:17 PM   #5
Join Date: Apr 2010
Posts: 4
Haha, nice. I think I'm just gonna do the upgrade since I'll prolly have to change it anyways, and I know I'm gonna add more electrical equ too. I'm also checking out some rebuilt and higher grade Alt's. I know Mean Green makes good ones, is there any other suggested manufacturers to consider?
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Old 09-23-2010, 05:44 PM   #6
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Posts: 4
Did this post get lost in Forum-space? lol
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Old 09-23-2010, 06:22 PM   #7
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Join Date: Sep 2010
Location: Southern Maryland
Posts: 27
Haha seems that way, I just don't know any places or Manufacture upgrades besides what I listed.. Sorry man..
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Old 09-23-2010, 07:53 PM   #8
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Location: Aurora, ON, Canada
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Might be the redtop. They're not ment to be cycled up and down with the a/c, winch, stereo, lights, etc. You might want to think about switching to a deep cycle battery. optima yellow top is better is you want to stick with the optima but any deep cycle RV battery is better then a standard car battery.

Just my 2 cents.
You're never to old to have toys!
'90 YJ, 4" RC Suspension lift, 1" Shackle lift, SYE and CV, Holley Carb, 33/12.50/15 Dynapro M/T's. RIP my old friend.
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Old 09-23-2010, 11:22 PM   #9
Join Date: Sep 2010
Location: Lakes Region New Hampshire
Posts: 101
Summit Racing has a 175 amp Tuff Stuff Alt. part #7510D for $265. That should be enough for your needs.

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alternator , alternator upgrade , battery , problem , voltage

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