97+ XJ Alternator Replacement

jay79cj7

New member
Two things:
1) My 00 XJ 4.0L has started to show the volt guage drop down to 12v or so when the engine is idling and a decent load is on the system. (different combinations of A/C compressor engaged, fan on high, headlights, etc.) It goes back up to 14v once I get moving. This never happened before and worry that its just going to get worse. I replaced my 6.5 yr old battery since it was due anyway, but its still doing it. Looks like my alternator is going? I don't want to be wearing my battery down on these cold Chicago winter days when I have my heater on full blast and not be able to start next time I need to.

2) Can you get the alternator out without having to take off the A/C compressor? It doesn't look like there is enough room to get it out, at least from the top. I haven't scoped it out from below.

Thanks!
 

Consider replacing with a 136A alternator from a late '90s fullsize Dodge truck or van, NipponDenso part #56027913. It's an easy bolt-in upgrade.
 
You can... I did a replacement, let me see if I can dig up the step-by-step and pics, wrote it up for a how-to article for the site, can't remember if I posted it or not... Not at all hard to do.
 
Re: 97+ XJ Alternator Replacement *BIG PICS*

Found it... This is the original tech article that I wrote up after doing my alternator.

Alternator Replacement Procedure

Subject Vehicle: 2000 XJ, 4.0 I-6 (with a/c)

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Let’s face it, we’re not all technically inclined, and if you’re anything like me, a sight like this, with your Jeep no longer working properly is pretty daunting… But trust me, this is maybe a ½ hour job if you’re really working it… I had never replaced an alternator, but after mine ate a little too much mud, it failed, and needed to be done…

Step 1: The Electric Fan
You’ll need to remove the fan to get the serpentine belt off, or at least, it makes it a lot easier… There are two little bolts on the top of the fan… Take these off, and then uncouple the electrical connection to the fan… The fan should then pull straight up (might take a bit of wiggling)… It’s not bolted at the bottom, just wedged in there…

Step 2: The Serpentine Belt
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With the fan out of the way, you now have access to the power steering pump assembly, which also happens to be the tension point for the serpentine belt. The first time I did this, I must have loosened about 15 different bolts before I figured it out… First, loosen the bolt circled in green… Don’t take the wheel off, just loosen it about 3-4 good turns. Then, you’ll want to twist the bold circled in red to the left… As you are turning this, the wheel you just loosened will be sliding down to the right, taking the tension off the belt… Loosen this enough to the point where you can slip the belt off the pulleys…

Step 3: The Battery Tray
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As you can see from the poorly drawn green cube, the battery is right in the way for this procedure… While it could be done with it in the way, it’s a lot easier if you’ve moved it… Plus, as you’re doing electrical work on the vehicle, you’ll want to disconnect the battery anyway. Take the wires off the battery terminals, and unclamp the holder on top of the battery… Once you have pulled out the battery, you’ll see three bolts holding the tray down that it sits on… These are going to be hard to undo, word of warning now… Once these bolts are off, the tray will come right off, opening up the engine compartment as you see in the picture… There is a small sensor mounted on the tray, just be careful not to break those wires when you are pulling the tray out. I left it connected, and just hung it off the side.

Step 4: Bolts Everywhere!
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Looks pretty daunting, huh? I saw all those bolts, and promptly freaked! 20 bolts holding this thing down?!? You’ve gotta be kidding me! But in reality, it’s a lot easier than this, as I found out, thankfully, before I started loosening everything in sight…

But first things first… On the back of the alternator, you’ll see a wire bolted to the back of it, and a wire harness plugging into it. These have to come off. Once you get them, there are a mere 2 bolts holding this beast on… The first picture references the top of the alternator; there is a long bolt toward the radiator, with a nut holding it on toward the back… Take the nut off, but don’t slide the bolt out yet. Now, in the second picture, you see a bolt on the bottom of the alternator… Take that one out. That’s it! Slide the top bolt out now, and the alternator can be wiggled down, then pulled out through the top. It’s in there pretty tightly, but it will come out if you rock it…

Step 5: Reassembly
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The only issue you may have with the installation of the new alternator is this little sleeve circled here… If it’s too narrow; it won’t fit into the top bracket, you can tap it back with a hammer and a screwdriver (or your tapping device of choice), it will slide ever so slightly… Line it up on the top, and slip that bolt back in there… Bolt the bottom in first, then the top. Plug in the wire harness to the back of the alternator, and bolt the wire back on to it (alternator should come with new nut for doing so)

**Word of advice**… Make SURE you compare the new and old alternators… You want to check bolt positions, wire plugins on the back, and the amount of grooves in the pulley… Your Jeep’s already broken, the last thing you need is more hassle!

Rethread the serpentine belt (we’re just going in reverse now of all the steps you just did, so you can check the previous steps for reference)… Tighten up the bolt that slides the pulley until the belt is good and tight. Once it is, tighten the bolt on the wheel. This locks it in place so it doesn’t slip and loosen.

Reinstall the battery tray, and the battery… This is a nice time to install a new battery, should you be so inclined.

Slide the electric fan back down, so it presses into the slots on the bottom… Bolt the top of it back in, and plug the connector in!

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Success! Notice how the charging system is back in it’s happy range: 13.5-14 volts… Before alternator replacement, it would not go above 12 volts (voltage of battery), and was steadily dropping until finally dying.

Congratulations! If you’re registering a charge on the system (or no battery light for those of you with no gauge), you have successfully installed your new alternator!

Related Note: If your vehicle is without battery for a while (in my case, three days), certain settings in the computer will be lost… As such, it may idle oddly, and feel like it is shifting strangely… Remember that the transmission “learns” how you drive, and adjusts settings accordingly… Give it a day or two, and it’ll be back to normal... And whatever you do, if you have the battery on a charger, do NOT cross positive and negative (hook them to the wrong ones). The battery, or the general electrical system that your charger is plugged into DOES NOT RESPOND WELL!!!

Hope this helps...
 

Thanks Saurian. I actually already did the job. By the way, for anybody else that needs to do this in the future, you don't need to take out the fan or the battery tray, although it probably would help to get at some things. I found that I could loosen the tensioner pulley with a box end wrench easily. It would probably be easier to reposition the serp belt without the fan, but I don't know if its worth the extra time to take out the fan and put it back in. Your call. If you pull the air dam out of the way down below, the alternator can be rotated and pulled out from below without much trouble. Different man, different methods. Thanks again.

By the way, a couple things I encountered: Autozone said they couldn't check my old alt, their computer couldn't do it. They also have my Jeep cross-referenced with a 117A model, but I know for a fact, from the Jeep dealer build sheet for my VIN, that I have a 124A alternator. Now 7A really shouldn't make or break you, but the fact that its the wrong rating could mean Autozone's computer is messed up and they would be giving you the wrong model. Compare new vs. old carefully. I never actually saw theirs to compare for myself.

Something else to check while you are doing the job is the condition of the wires themselves. A bad ground or a bad lead from the alt to the battery can also cause problems. Check for a voltage drop between the postive terminal of the alt and battery (across the wire connecting the two) and from the negative battery terminal to the alt case. The instructions with my alt say that anything over 0.25V means trouble.

Now that I have a new alternator, the system maintains 14v under a full load at idle, so that confirms the old aternator was starting to go.
 
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