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Old 03-25-2016, 11:25 AM
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Changing out alternator

Need to change out the alternator on my 91 2.5 (no AC). Looks straight forward. Is it possible to do without loosening the tensioner on the ps bracket? Just curious if could be done. Any tips or tricks from the gurus? Thanks in advance!

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Old 03-25-2016, 02:42 PM   #2
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My Jeep is a 6 cyl, so I am simply guessing.

I would loosen the alternator and slip the belt off if possible.
By looking at my Factory Service Manual, it looks like there are two separate belts.
Once you have the belt off the alternator, the rest should be easy.

Don't forget to disconnect your battery prior to loosening your alternator.

Good Luck, L.m.

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Old 03-25-2016, 02:52 PM   #3
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Might want to look into a more powerful alternator if you have added extra lights or other power draws. I went from a 90 amp YJ to a 140 amp Grand Cherokee and it makes a huge differance. In my case it was a bolt on with the only thing I changed was heavier wires (called the big three) from + alternator to battery and -battery to block and firewall and - alternator to block.
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Old 03-25-2016, 04:52 PM
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Just got it out. Took about 20 minutes. When I put the new one in, should coat all the electrical connectors with dielectric grease?
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Old 03-25-2016, 04:58 PM   #5
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Always squish a drop or two of dielectric grease into any connectors whenever you have them unplugged.
It helps to keep water out of the connections and thus prevent corrosion. Works better than Vasaline on your battery connections also.

Good Luck, L.M.

Good Luck, L.M.
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12K Badlands winch with dual batteries.
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Old 03-25-2016, 05:00 PM   #6
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Yes! Also check the wires for corrosion, if it's green just outside the insulation it may be green several inches up. I changed all my wires.
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Old 03-25-2016, 05:02 PM
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Quote:
Originally Posted by Luckymac View Post
Always squish a drop or two of dielectric grease into any connectors whenever you have them unplugged. It helps to keep water out of the connections and thus prevent corrosion. Works better than Vasaline on your battery connections also. Good Luck, L.M. Good Luck, L.M.
Lots of connectors.
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Old 03-25-2016, 05:41 PM   #8
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See the green corrosion on the end of that wire? I can pretty much bet that corrosion goes up the wire under the insulation. Does it have to be changed? No, but it will help the alternator give the most current.
P.S. That is the wire that charged your battery
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Old 03-25-2016, 05:44 PM
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See the green corrosion on the end of that wire? I can pretty much bet that corrosion goes up the wire under the insulation. Does it have to be changed? No, but it will help the alternator give the most current. P.S. That is the wire that charged your battery
If I open the loom, will it trace back directly to the positive battery terminal?
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Old 03-25-2016, 05:51 PM   #10
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I believe on yours it will go back to the PDC box and the PDC goes to battery +. You don't need to follow that route. You can run a new wire from battery+ to that alternator post, you just need to put a 150 amp Bussmann fuse between them and be sure you use the same gauge wire for the ground.

If you go this that corroded red wire should have a plug between the PDC and the alternator, you can just unplug the alternator end and leave the part coming from the PDC.
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Old 03-25-2016, 07:21 PM
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Originally Posted by reno92 View Post
I believe on yours it will go back to the PDC box and the PDC goes to battery +. You don't need to follow that route. You can run a new wire from battery+ to that alternator post, you just need to put a 150 amp Bussmann fuse between them and be sure you use the same gauge wire for the ground. If you go this that corroded red wire should have a plug between the PDC and the alternator, you can just unplug the alternator end and leave the part coming from the PDC.
It does lead to a plug before it goes into the box..
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Old 03-25-2016, 10:50 PM   #12
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If you're comfortable re-wiring go for it, if not just replace the wire from the plug to the alternator.
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Old 03-26-2016, 02:07 PM
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The old alternator tested bad, as I figured it wouldI put the new one on and started right up. Volts on gauge showed 13-14 for a few seconds, then dropped to around 8 and check engine lite came on. The new alternator makes a weird whizzing noise the goes up and down in pitch. I cleaned and greased all the connections. Belt is tight. I'm stumped now. Battery is a month old. No other low voltage type problems other than check engine light, code 41. If I let it sit then restart, volts go to 14 for a few seconds then drop to 8. Any suggestions? After a few minutes the whizzing noise stopped.
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Old 03-26-2016, 02:24 PM   #14
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If it's a rebuild its not uncommon to get a bad one right out of the box. It could also be the wiring, either a bad ground or that corroded positive wire. Does your year have the voltage regulator built in the alternator or separate?
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Old 03-26-2016, 02:28 PM
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Originally Posted by reno92 View Post
If it's a rebuild its not uncommon to get a bad one right out of the box. It could also be the wiring, either a bad ground or that corroded positive wire. Does your year have the voltage regulator built in the alternator or separate?
I think the 91 is externally controlled by the computer. It is a rebuild.
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Old 03-26-2016, 03:02 PM
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I've got a week to work on it. Im going to try and replace the wiring and see if that helps.
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Old 03-26-2016, 07:13 PM   #17
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Just food for thought but about a year ago the alternator in my van started making the same noise and showing low voltage. Shortly after, the alternator quit working so I figured it was defective (it was). After putting in a new one the same symptoms returned so I dug a little deeper and found a wire to my auxiliary power supply was shorting out. I re-taped the connector and that took care of the problem. Worth a try and good luck, Dave
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Old 03-28-2016, 08:41 AM   #18
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Clean off the corrosion inspect the wire WELL.. If you have slack in the cable you can simply chop off the last few inches and install a new connector. Too bad your In Ohio I have a good alternator I would give away.
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Old 03-28-2016, 10:35 AM
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Clean off the corrosion inspect the wire WELL.. If you have slack in the cable you can simply chop off the last few inches and install a new connector. Too bad your In Ohio I have a good alternator I would give away.
I put a meter on the alternator. 12-13 volts at idle. Under load (lights and fan) 11 volts. Battery with engine off 12 volts. Headlights are not dim, engine cranks fast and starts immediately. The alternator appears to be functioning worth those readings, correct? Continuity between + terminal on alternator and positive battery terminal is .5 ohms.
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Old 03-28-2016, 11:35 AM
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Originally Posted by TigWizard View Post
I put a meter on the alternator. 12-13 volts at idle. Under load (lights and fan) 11 volts. Battery with engine off 12 volts. Headlights are not dim, engine cranks fast and starts immediately. The alternator appears to be functioning worth those readings, correct? Continuity between + terminal on alternator and positive battery terminal is .5 ohms.
Updated figures using a pro meter from a neighbor (did not trust old analog meter).
Battery engine off 12.8
Battery running 12.3
Battery under load 11.8
Alternator running 12.8
Alternator under load 11.8 (over two minutes, no change)
Continuity from + alternator to + battery (negative disconnected) .5 ohms
Check engine light on code for alternator field
Dash volt gage who's 8 volts approx
With engine running, headlights bright
Cranks and starts as normal

Sorry for all the questions. Just trying to zero in on the problem.
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Old 03-28-2016, 11:45 AM   #21
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Alternator should put out 14 volts even under load.

If it is externally regulated by ECM check wiring to ECM.

Problem is either that wiring or ECM and consistent with error code.
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Old 03-28-2016, 12:32 PM
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Alternator should put out 14 volts even under load. If it is externally regulated by ECM check wiring to ECM. Problem is either that wiring or ECM and consistent with error code.
Is it possible the new (reman) alternator is bad?
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Old 03-28-2016, 12:39 PM   #23
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I have got a few new ( reman ) alternators that were bad. Coincidently all from O'reillys.
Starters too
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Old 03-28-2016, 01:27 PM
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I have got a few new ( reman ) alternators that were bad. Coincidently all from O'reillys. Starters too
Just took it to get tested. Tested good 3 times 14.7 output under load. Guess I'll keep looking. I cleaned and greased all the grounds. I took the wires out of the loom and removed all the tape. The wires look good all the way back to the under hood fuse/relay box. All mega fuses are intact. I gently cleaned the legs of all the mega fuses with steel wool. Engine and chassis grounds are clean and tight. I'm thinking it's the ecm. Might try to rig up an external regulator. Thanks for the help guys!

Ps is the jeep still safe to drive, or will the battery eventually go bad. I'm not planning on driving it, but just in case. Short trip to the liquor store maybe! I need a drink!
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Old 03-28-2016, 03:27 PM   #25
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Battery will eventually go flat.

Need more than 12.6 volts out of the alternator to maintain the battery.
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Old 03-28-2016, 03:32 PM
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Battery will eventually go flat. Need more than 12.6 volts out of the alternator to maintain the battery.
What I thought! Battery only a month old. I'll wait for regulator and go from there. Regulator is $60. ECM is $200. It's always something!
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Old 04-05-2016, 05:22 PM
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Installed the external regulator. Running 14.3 at idle 14.8 under load. Now I just need to install the little filter thing that connects to the original field wires to turn off the check engine light.


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