• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Alternator or Bad Ground?

M

Markos

NAXJA Forum User
Location
Seattle, WA
Hi Folks,

Recently my jeep died while a relative was driving it. She tried to jump it and let it idle but it wouldn't stay running. I drove down to meet her, jumped it, and drove it back home about 15 miles without issue. I then proceeded to drive it another two days without issue.

Today, the battery is at 9 volts while out to lunch. I took it to Autozone and the guy said the alternator isn't charging at all. Seeing that this problem is intermittent, I'm wondering if it's actually my alternator, or perhaps a bad ground.

Other suspicions for bad ground:
Volt gauge dropping from 9 to zero
Check Guages light turning on
Check Engine light turning on
Inline 30amp ground kill switch has been running hot over the past 6 months, replaced it twice. Was fine for years before that.
1yo Oil Pressure Sending Unit pegged at 80
 
A bad ground in your Jeep cause the alt to fail the test ? Intermittent failure might be the brushes, or a wiring issue in the Jeep.

Re-test at another store, or just get a new alt.
 
Well I'm not sure. I'd honestly rather just replace the alternator right now, but I don't want to spend the time doing that and have it happen again next week. I just want to vet the scenario with the forum first before picking up an alternator. Thanks for the info about the brushes, I didn't know that could be the culprit.
 
Just check your grounds. Clean them up if they're dirty and replace them if they're broken. Also, check your power wire from the alternator to the PDC. Also, test the battery to make sure that it's good. A bad battery can do some funky stuff.
 
Did you have Autozone test your charging system in the parking lot, or did you remove the alternator and have them "bench test" it.

If you had them bench test the alternator and it failed, replace the alternator.

If you had them test with alternator installed, refresh your grounds and alternator connections and if this continues, replace your alternator.
 
Apologies for the lack of details. '99 4.0 with 185K on the original alternator. I ran it most of the way home from work on the battery and it died about a mile from the house. I picked up a 136 amp ZJ alternator from Autozone this evening. I'll check the grounds before I swap out the alternator. I also plan on updating the grounds. I'm either going to ordre a kit from 5-90, or piece together new cables myself. The Autozone test was on the vehicle, not a bench test. Thanks for the help!
 
Markos said:
Apologies for the lack of details. '99 4.0 with 185K on the original alternator. I ran it most of the way home from work on the battery and it died about a mile from the house. I picked up a 136 amp ZJ alternator from Autozone this evening. I'll check the grounds before I swap out the alternator. I also plan on updating the grounds. I'm either going to ordre a kit from 5-90, or piece together new cables myself. The Autozone test was on the vehicle, not a bench test. Thanks for the help!
Click to expand...

Couple of things before you do the swap...

Remove the battery and the battery tray. It will make the swap a lot easier, and it won't take you more than a couple of minutes to do that first....

Put both alternators side by side on the bench, before you install the ZJ one. Some of the higher amp alternators are bigger in diameter than the stock ones, and they won't not fit in the mounting bracket. Just a little difference in diameter, will prevent the alternator from seating in the mounting bracket.

Also, make sure the pulleys are the same size. If not, swap your original pulley over the the other alternator, or your serpentine belt won't fit. You won't need a pulley puller, as it should just slide off once your remove the mounting nut.

I ran into both these issues just last week, swappping in an alternator in my '98, which had 154k on it.....just saving you some grief.
 
The higher amperage alternator most likely won't fit. However, you can make it fit by grinding a bit off the bracket, engine block and timing cover. You need just enough room to see daylight between the alt and block /mount.
 
You wont need to grind any material off the block. Remove the stamped steel and aluminum mount and test fit the alternator. You will need to radius both brackets to allow for the larger alternator case.

OP: upgrading the battery cables and charging cable PDC to alternator is required along with installing a fuse across the PDC studs to replace the fusible link.
The swap of the pullies is necessary since the ZJ pulley is slightly larger and would spin the alternator slower. The field wiring terminals a redifferent and will need to be adapted by changing terminal ends. The charging stud insulator will need to be swapped old to new due to orientation.

Before you change alternators you should check the field charging leads on the back towards the bottom of the alternator to ensure the are clean and tight. These connections are how the ECM regulates the charging rate.
 
CharlesS said:
You wont need to grind any material off the block. Remove the stamped steel and aluminum mount and test fit the alternator. You will need to radius both brackets to allow for the larger alternator case.
Click to expand...
The block and timing cover are between these two brackets and will also have to be modified.
 
Thanks for the extra bit of info. I haven't heard anything about grinding the block or timing cover. I have a '99, and planned on using this writeup I found on jeepforum:

http://www.jeepforum.com/forum/f11/5-9-alternator-upgrade-642951/

It looks like the bracket grinding should only take a few minutes. Interestingly enough, I went to O'Reily's last night to get the alternator. They had two different case sizes for the 136a alternator. One was 4.x" and the other was 5.x". They didn't have it in stock so I got one from Autozone. They didn't specify the different sizes.
 
Talyn said:
The block and timing cover are between these two brackets and will also have to be modified.
Click to expand...

When I installed the ZJ alternator on my '98 XJ I didn't need to modify the block or timing chain cover; only the the aluminum and stamped steel brackets which I modified off the vehicle.
Not sure what size alternator you have, but mine fit perfectly with only modifying the brackets.
 
CharlesS said:
When I installed the ZJ alternator on my '98 XJ I didn't need to modify the block or timing chain cover; only the the aluminum and stamped steel brackets which I modified off the vehicle.
Not sure what size alternator you have, but mine fit perfectly with only modifying the brackets.
Click to expand...

Perhaps instead of being special you picked up the 136amp alternator with the smaller case. As I mentioned early on there are two different cases. One case is 130mm and the other is 137mm. That's over a quarter inch difference, and could certainly account for the block grinding requirements. I'm hoping that I picked up the smaller one.
 
Talyn said:
Everyone that I have heard do this mod has had to grind the block as well. Including on my 2000.

http://www.naxja.org/forum/showthread.php?t=80953

http://www.naxja.org/forum/showthread.php?t=951605
Click to expand...

FYI - I finished this up today and I did in fact need to grind the engine block, as well as the steel brace that bolts to the alternator bracket. The block grinding was a non-issue, and actually went faster than the aluminum bracket. I went with a 160amp alternator from an '03 durango, which is the same size as the 136amp ZJ unit.
 
You must log in or register to reply here.

Similar threads

D
What Is This Part On 96 XJ Alternator?
2
Replies
21
Views
3K
DirtySouthXJ
D
T
Random Starting Issues - ECU / PCM Problem?
Replies
12
Views
2K
TEX-J99
T
W
1999 XJ - No start - PCM?
Replies
1
Views
2K
Tim_MN
Tim_MN
M
92 With Code 12 & 41 (did not touch battery) and running rough (intermittently)
Replies
3
Views
904
90xj06
9
R
2000 XJ Sport - Trying to diagnose intermittent sputtering
Replies
0
Views
1K
ramonesrazor
R
Back
Top