Topic: Replaced the alternator twice ... electrical gremlins persist.

[Sine Deviance]

Okay... I am having the weirdest problem ever. I'll just start at the beginning. Jeep is a '95 YJ with a 2.5L.

We're out of town for Christmas vacation. My Jeep's alternator apparently stopped charging and yesterday it went dead while I was driving it. Today I replaced the alternator and it didn't work. So I replaced the new alternator with another new one and again it didn't work, so it's not the alternators causing the problem. They both passed the bench test (the original alt did fail though.)

After alternator #3 I had them check it while the Jeep was running. Their little computer says that the cause of the charging system failure is that the voltage regulator has failed. I am to understand that the voltage regulator is on the PCM. I do not trust their little computer 100% because the Jeep otherwise runs fine, and it seems to me that if the PCM was shot it would be running in limp mode or wouldn't crank up at all. They also tested my battery and it was good. That was to be expected considering it's a new battery.

I checked all of the main fuses in the fuseblock under the hood. None of them are fried. They all passed a test light check.

Is there anything else I should check in the morning before I make the call to have it towed back to home? Do you guys think it's the PCM? Can I install an aftermarket voltage regulator and get this thing charging like it should?

Any help would be really appreciated, I'm kinda screwed right now. Thanks!

[Jeffy]

Ehhh, that's not a good sign.     I'd order a PCM or better yet, borrow one if you can and see if that fixes everything.  My guess is either the alternator spiked and took out the PCM circuit or the PCM circuit died and took out the alternator.

[Torch_Ind]

my 95 had a big connector farther down that went completely green inside and wouldn't pass amperage throw it. had to clean it out

as for the regulator I'm pretty sure you can get a external one for it but unsure witch one you would need.  I know fords and others have used external ones so would be a matter or wiring it up to it.

[Sine Deviance]

Some extra stuff I forgot to add in (gotta love stress!) Before I even walked out the door with either of the new alternators I had them bench checked. They both passed. However, after I swapped the first new one for the second new one, they bench checked the first new one again and it failed the checks three times. So either that alternator was a bum alt off the shelf, or my Jeep somehow killed it.

Ehhh, that's not a good sign.     I'd order a PCM or better yet, borrow one if you can and see if that fixes everything.  My guess is either the alternator spiked and took out the PCM circuit or the PCM circuit died and took out the alternator.

Hated to read that, but thanks so much for the reply I can order one from the auto parts store down at home for $250 and it won't be here for two weeks. Is there somewhere else I could order one that would be cheaper/faster? Borrowing one or junkyard aren't an option unfortunately, we have no Wranglers in the yards here because they all got cubed during C4C.

[Jeffy]

Some extra stuff I forgot to add in (gotta love stress!) Before I even walked out the door with either of the new alternators I had them bench checked. They both passed. However, after I swapped the first new one for the second new one, they bench checked the first new one again and it failed the checks three times. So either that alternator was a bum alt off the shelf, or my Jeep somehow killed it.

That's very common, especially for rebuilds.  I would have gone with a 136A minimum as it is drop-in and costs the same as the 90A.  Also, I think 136A's are more commonly used on most GC's as well as Dodges so there would probably be more turn over then the 90A.

Check www.car-part.com.

[Sine Deviance]

That's very common, especially for rebuilds.  I would have gone with a 136A minimum as it is drop-in and costs the same as the 90A.  Also, I think 136A's are more commonly used on most GC's as well as Dodges so there would probably be more turn over then the 90A.

Can I get the 136A at an auto parts store like Autozone? Also, the 90A I got cost $118.99 + tax with the core return. That was the cheapest. Would the 136A really be the same cost?

[Jeffy]

Can I get the 136A at an auto parts store like Autozone? Also, the 90A I got cost $118.99 + tax with the core return. That was the cheapest. Would the 136A really be the same cost?

All of the alternators on the charts are OEM alternators that are drop-in.  They should all cost roughly the same even though some are rated higher the others.  To the mfg. they are basically the same.

[Sine Deviance]

Okay. Well, new PCM first, then I'll worry about the alternator. I still have lots of stuff I want to do on this Jeep. After I get this problem fixed, I'm going to be saving up for the PosiLok cable and the E-Fan swap. I wanted to get some 19# injectors too, just haven't had the money. Oh, and then I need to replace the motor mounts. And THEN it needs a new exhaust system from the engine back.

Man, all this stuff is going to add up to around $1,500. A good aftermarket header alone is $400. I'm gonna have to rob a bank

[sharpxmen]

did you re-check the last one? i have a feeling is not the PCM (spidy sense) - oh well, it could be. if it doesn't throw a code you could use an external regulator (i think) but you'll have to make the connection and i wouldn't cut the wires just yet as it could be something else.

I would at least test the connectivity from pin 20 on the PCM connector (it's a Dark Green wire and is the alternator control driver) to the alternator - use a multimeter, and if there's no connectivity then there's your problem - if the connection is good then start the engine and measure the voltage you get to this wire at the alternator - if there's no voltage then yeah, seems that the PCM alternator controller is shot, if you get voltage then stop the motor and then put the ignition on - i belive in this case it should show 0v (i'm not 100% on this but i think if you have full 12v with only the ignition it means it's fried) - if all this checks out i don't think is the PCM but the alternator again or the connection from the alternator to the battery.

EDIT: there are 2 things that can go bad in these alternators: the brushes or the diodes - I don't think the PCM can fry either one of them (maybe if you have full 12v at the generator driver wire), but a short could also damage the diodes i think (on the 12v power wire that comes out of the alternator going to the PDC) - so you might want to check that as well, although in that case there are 2 x 50 amp fuses in the PDC that would blow so you would see that - very surprising that the first one you had tested bad after being on the Jeep.

[dwtaylorpdx]

Its an easy test, just disconnect the field wire to the alternator and see if it has voltage on it with the engine running.

According to a jeep mechanic I happened to talk to a couple weeks ago a LOT of the mid 90's Chrysler rigs
blow this circuit from the ECU due to the load on it and age.

You can replace it with a variety of "one wire" alternators from custom sources...

On the other hand my original alternator lasted about 150K I have yet to get 20K out of a rebuilt...arrg! 

Dave

[Sine Deviance]

did you re-check the last one? i have a feeling is not the PCM (spidy sense) - oh well, it could be. if it doesn't throw a code you could use an external regulator (i think) but you'll have to make the connection and i wouldn't cut the wires just yet as it could be something else.

I would at least test the connectivity from pin 20 on the PCM connector (it's a Dark Green wire and is the alternator control driver) to the alternator - use a multimeter, and if there's no connectivity then there's your problem - if the connection is good then start the engine and measure the voltage you get to this wire at the alternator - if there's no voltage then yeah, seems that the PCM alternator controller is shot, if you get voltage then stop the motor and then put the ignition on - i belive in this case it should show 0v (i'm not 100% on this but i think if you have full 12v with only the ignition it means it's fried) - if all this checks out i don't think is the PCM but the alternator again or the connection from the alternator to the battery.

EDIT: there are 2 things that can go bad in these alternators: the brushes or the diodes - I don't think the PCM can fry either one of them (maybe if you have full 12v at the generator driver wire), but a short could also damage the diodes i think (on the 12v power wire that comes out of the alternator going to the PDC) - so you might want to check that as well, although in that case there are 2 x 50 amp fuses in the PDC that would blow so you would see that - very surprising that the first one you had tested bad after being on the Jeep.

I will check that stuff once I get the Jeep back down here, thanks. I did check both the 50A alternator fuses and neither were blown, so I don't think it's a short. But we'll see, I'm sure.

Its an easy test, just disconnect the field wire to the alternator and see if it has voltage on it with the engine running.

According to a jeep mechanic I happened to talk to a couple weeks ago a LOT of the mid 90's Chrysler rigs
blow this circuit from the ECU due to the load on it and age.

You can replace it with a variety of "one wire" alternators from custom sources...

On the other hand my original alternator lasted about 150K I have yet to get 20K out of a rebuilt...arrg! 

Dave

I already tried disconnecting the negative from the battery while it was running to see if the alt was charging at all. The engine stalls right away so something is definitely keeping the alternator from engaging or burning it up as soon as the engine is first cranked over. Odd problem, this.

[sharpxmen]

I already tried disconnecting the negative from the battery while it was running to see if the alt was charging at all. The engine stalls right away so something is definitely keeping the alternator from engaging or burning it up as soon as the engine is first cranked over. Odd problem, this.

you should never do that if you suspect your alt or regulator to be bad - you could fry the vehicle electronics (radio, PCM, etc) - one reason can be overvoltage if your alt field regulator does not regulate the voltage (repeated myself there but i couldn't find a better way to express what i wanted to say).

[Sine Deviance]

you could fry the vehicle electronics (radio, PCM, etc)

Yeah, but since the PCM is apparently already fried, it wouldn't make much difference to do it that one time