1995 yj alternator question - JeepForum.com
 
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post #1 of 7 Old 09-22-2019, 08:30 PM Thread Starter
wpatters1229
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1995 yj alternator question

I have a 2.5 engine without AC and the alternator is not putting out anything. If I measure between the ground and the positive post on the alternator it is putting out about 28 volts. One post of the connectors that go to the regulator has the same voltage that is measured at the battery, 11.84 volts. The other post is a low 4 or 5 volts. I took the alternator to two auto parts stores and they both said it past the test they perform. The replacement alternators show having an external voltage regulator but I can not find any on the jeep. There is an engine control module but can't seem to find it anywhere. The fuse and relay block is about all that is findable (if that is a word).
I have gone on the internet and I get conflicting answers that the alternator has an internal voltage regulator. I just am not sure now. I do not want to replace the alternator at $123 and find it did not fix anything. They do not let you return it if installed.
SO THE QUESTIONS IS: Does this year jeep yj have an external voltage regulator and if so where is it.

Thanks

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post #2 of 7 Old 09-22-2019, 08:57 PM Thread Starter
wpatters1229
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I was just looking around the Internet and have come across alternators that apparently will fit my '95 wrangler. They say they have internal regulators. I am starting to go nuts trying to figure out if I need to replace the alternator I have with one that has the internal regulator or one that has an external regulator. The alternator in the jeep is a Denso 56005684. it puts out about 28V on the plus connector. But nothing on the battery.
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post #3 of 7 Old 09-22-2019, 11:06 PM
mukluk
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The stock alternator on a '95 YJ is externally regulated by the PCM. Your alternator should not be putting out 28 volts, the fact that it is points toward either a fault with the regulator control circuit in the PCM or the dark green field control (also called the generator field driver) wire is shorted to ground. Since you aren't actually getting those 28 volts to the battery, that would indicate either a wire connection problem between the alternator, PDC, and battery, or fuses 2 and 6 (50amp) in the PDC are blown. Continuing to run the Jeep with the alternator cranking out high voltage will damage the alternator, and fixing the feed wiring to the battery before fixing the regulator problem can cause the battery to overcharge and possibly explode.

I would recommend first disconnecting the PCM connector (C139) and field wiring at the alternator (C120) then checking the dark green field control wire to see if it is shorted to ground -- find and repair the short as required. If the field wiring checks out good, chances are decent the regulator in the PCM is bad in which case you can either install an external regulator or replace the PCM. Once the alternator regulator is functioning as it should again, proceed with tracking down the issue with the feed wiring or fuses from the alternator to the PDC and battery.
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post #4 of 7 Old 09-23-2019, 08:43 AM Thread Starter
wpatters1229
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This is a great response to my inquiry. Much appreciated.

Is the PCM located on the right side of the firewall just next to the brake vacuum booster?
shows this location. I also see a connector that looks like A11 but could not get it apart to inspect. First thing I did was check the two 50 amp fuses. All good. My gut says the PCM is bad. The jeep runs fine. It did have a code 41 engine check light but after taking out the alternator and putting it back that check engine light does not show up anymore.
If I get a new alternator with an internal voltage regulator, how would that affect the PCM and the regulator circuit it contains? The PCMs are not cheap.
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post #5 of 7 Old 09-23-2019, 08:52 AM
jtec
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did you check the fuses or did you check the circuit?
In the amazingly helpful diagram provided by mukluk - notice the fuses can be good BUT the wire to alt is open even unplugged.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 7 Old 09-23-2019, 03:29 PM
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The PCM is located outboard of the brake booster, yes, on the left side of the firewall -- location should always be referred to in relation to the vehicle, not the person's point of view. Also, there is no connector A11, that notation is the circuit designation. The particular connector in the alternator to PDC feed doesn't have a specific connector label.

Before condemning and replacing any parts you need to perform the wiring check advised earlier. Shortcuts in troubleshooting can get costly rather quickly.

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post #7 of 7 Old 09-23-2019, 06:47 PM Thread Starter
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I finally did some more step by step checking starting with voltages while the jeep is running and found the output of the alternator on the 12+ to be 1 volt but the two terminals that go to the PCM seemed to have one with the same voltage as the battery and the other at around 5 v which I assume had to be a trigger input to the alternator. The fact that the 12V+ lead was not producing lead me over to the fuse box again. This time I took out the three 50amp fuses and probed at each side. On two of them I saw the same 1 v and the other side the battery voltage. I then jumper across the connection and saw the voltage on the alternator 12v+ lead change to 14.5v. I looked again at the fuses and one had a crack it in and if you moved it (wiggle) you could see the ohms change. I jumpered all the 50 amp fuses and everything worked. Apparently old fuses are problematic. I left the jumpers in and have ordered new fuses off Amazon as you can get 5 for $5.99 versus one for $4.99 at the local parts store. And they wonder why Amazon is the place to go if you don't need it instantly. What a Cluster F#$%. Almost paid $123 for a new alternator and then thought it might be a bad PCM...even more $$$. Thanks for the diagram and all the advice!!!
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