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Voltage Regulator Issue


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I’m in the process of a OBD1 HO swap into my 88 MJ. 

 

The parts XJ I bought, a 93, had an external voltage regulator. I assumed someone had put it in not knowing that the PCM handles the voltage from the alternator. With the swap just about done, the alternator in the MJ is not charging the battery. 3 Alternators, and no go. I installed the aftermarket regulator from the XJ to see what would happen and just like that, it was charging at about 14.8 volts. Is this indicative of a failing PCM? Maybe something else could cause this issue? Could it be potentially bad to run this external regulator? Another issue is, the truck will not crank with it connected. Very strange issues. Help is appreciated.

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I don't know much about the HO Jeeps because I've only ever owned one (and it was actually sorta new then), but the voltage regulator failing in Chrysler PCMs is super common in their other vehicles.  Most people slap an external regulator on them and motor only happily into the sunset with no other issues.

 

When you say it won't crank with 'it' not connected, what exactly do you mean?  With the external regulator not connected?  With the PCM not connected?  With the alternator not connected to the PCM?  By 'crank' do you mean it won't turn over (the correct definition), or that it will not fire/run?

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2 minutes ago, DirtyComanche said:

I don't know much about the HO Jeeps because I've only ever owned one (and it was actually sorta new then), but the voltage regulator failing in Chrysler PCMs is super common in their other vehicles.  Most people slap an external regulator on them and motor only happily into the sunset with no other issues.

 

When you say it won't crank with 'it' not connected, what exactly do you mean?  With the external regulator not connected?  With the PCM not connected?  With the alternator not connected to the PCM?  By 'crank' do you mean it won't turn over (the correct definition), or that it will not fire/run?

It won't turn over with the external voltage regulator connected. Should have been more clear. I'll tool around with it  bit more, but if it's alright to run an external regulator, than that's probably what I'll do. PCMs are expensive, haha. 

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One was a NAPA 90amp PN: 213-8613. I'd have to check the one that's currently on it later. OEM replacement for a 93 XJ, all the mounting brackets came from the 93, so a RENIX wouldn't fit, nor would it plug up. Connectors are very different. I'm beginning to think the no start is not an alternator or regulator issue, it might just be a coincidence. If the computer is bad, I'd imagine that would cause frequent no crank scenarios. 

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5 minutes ago, PFCLeist said:

One was a NAPA 90amp PN: 213-8613. I'd have to check the one that's currently on it later. OEM replacement for a 93 XJ, all the mounting brackets came from the 93, so a RENIX wouldn't fit, nor would it plug up. Connectors are very different. I'm beginning to think the no start is not an alternator or regulator issue, it might just be a coincidence. If the computer is bad, I'd imagine that would cause frequent no crank scenarios. 

 

Yeah, the Renix brackets are actually getting harder to find now.  I need to get a stash of them going.

 

Could just be a starter that's on its way out.  Tap it with a hammer?  Or check that it's getting power to the solenoid when in the crank position.

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15 minutes ago, DirtyComanche said:

 

Yeah, the Renix brackets are actually getting harder to find now.  I need to get a stash of them going.

 

Could just be a starter that's on its way out.  Tap it with a hammer?  Or check that it's getting power to the solenoid when in the crank position.

It's already been bench tested from the last issue I was having with a no crank. Turned out to be a fuse and turned over everytime. 

 

14 minutes ago, HOrnbrod said:

Have you tried checking for OBD1 fault codes?

 

https://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

I will absolutely try this next chance I get, thanks. The video in the link is incorrect, though. 

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37 minutes ago, HOrnbrod said:

 

Thanks - video is history.

I'm getting 34 (cruise control)12 (battery d/c in last 50 cycles) and 55. It didn't even have cruise control, haha.

 

Edit: I'm also getting 41 (An open or shorted condition in the generator field control circuit) That sounds like my problem. Is that ANOTHER bad alternator?

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2 minutes ago, HOrnbrod said:

Normal. Well, was worth a shot..

 

Sorry, edited my last post. I'm also getting 41 (An open or shorted condition in the generator field control circuit) That sounds like my problem. Is that ANOTHER bad alternator?

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That's just a molded connector that attaches to the two alt field terminals if that's what you mean. I've never heard of one going bad, but you could test the wires going through it for continuity. Remove the connector from the alternator and ohm it out from the ring terminals to each wire using a sharp meter probe to pierce through the wire insulation.

 

On some Chryco vehicles using this same ND alternator, that molded connector isn't used at all; the wires are just connected to the alt with ring terminals.

 

ALTERNAT_html_a804cdf.jpg

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Little black box? The external regulator?
I’m not sure how the external bypass was done. Not a uncommon problem. There are kits and plenty of instructions. My guess is something is wired wrong or failed in the external set up. Maybe it never worked, might be the reason it was sold as a donor car.
I’d try to match up the part # on the box you think is bad or get one of the kits and redo it to their instructions.



Battery cables can be another big issue.

the 93 PCM ought to be pretty cheap to find used, rebuilt will still be expensive, used should be fairly cheap now a days.


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This is what I've got:

aYip6d4.jpg

Sorry for the hard to read overlay, but there is what I assume is a bracket on that black insulation that has no continuity over ground or positive. Ground is good, and I'm getting 12 volts from the B+ terminal wire. The field terminal seems to have a varying voltage, which would make sense I suppose. The external voltage regulator is not charging the battery, anymore, either. I'm thinking my third new alternator is fried. My patience is going the same way. 

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I don't know how you got the "black box" connector off the end of the engine wiring harness unless the PO cut it off for the external regulator. Where are the two field wires from the engine harness entering the "black box" molded connector? According to my FSM, one wire is GRY; the other GRN/RED. They are supposed to be in the wiring harness and entering the molded connector at the yellow arrow in the 2nd picture.

5a9f01d15d1fb_134AAlternatorRearView.jpg.0acd8a15c3d225a8eabf10c633b1354b.jpg

5a9efec926627_134AAlternatorRearView1.jpg.dc5dd6930378b0ea2720b6c8aecdd292.jpg

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They are there, they route up to the engine bay harness at a connector. The picture doesnt show it very well. The regulator he used just had two ring terminals ontop of the field terminals. It is still connected to the engine harness in this picture. 

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