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callbox47 01-24-2011 07:16 PM

Alternator Insanity
Two days ago the lights go dim, headlights, instruments lights, check engine light comes on, but I make it to work. I can't take the vehicle to get anything tested, but I am able to get an alternator and manage to get it swapped out. It seems to work, but on the way home the next day, the check engine light comes on again.

So I take it to the local auto parts store where they test the old alternator (bad) and the new one on the jeep (also bad). So I buy a second alternator, go home and take the new alternator off, but before I put the second new one on, I decide to take it back to the auto parts store and test it again off the vehicle.

It now tests good.

I checked all the fuses, fuseable links, checked the positive and negative voltage drops, and checked the voltage across the fields which reads 2.17 volts but all indications say should read ~5 volts.

This tech bulletin which comes with the alternator: Online Technical Support Center explains the circuit, however there is no indication on the alternator as to which contact is field 1 and which is field 2, (and the picture looks nothing like the back of the alternator.)

The voltage varies between ~10 and ~16+ when running but the engine quits when I disconnect the battery.

With the ignition on, there is no voltage to either contact (which to me there should be to one, and that would tell me which is field 1.)

From what I can find on the net the voltage is regulated by the ECM according to this thread:

So at this point, is there anything I can do to actually test the ECM other than to buy one for $200 and try it?

Also, flashing codes:
12 - battery disconnect within last 50 key cycles
33 - A/C clutch relay (vehicle does not and has never had A/C and there is no A/C relay present in the fuse box)
41 - Alternator field
46 - Battery under volt (doh)

Thanks greatly for any relevant advice or directions you can give me.

callbox47 02-05-2011 11:59 AM

Alternator Testing
4 Attachment(s)
Below shows the back of the alternator from the right side of the engine looking toward the front of the vehicle. The black wire is the jumper for Field 1, (the Field 1 tab is hidden behind) the yellow wire is the jumper for Field 2. The large red wire is the Alternator output.

(The single tab, just to the right of the lower black alligator clip is the Field 2 tab connector that would be on the Field 2 post where the Yellow alligator clip attaches) and the large tab to right of the lower arrow is the ground that goes the alternator ground post.

Attachment 36991

Next is the voltage test of Field 1 not grounded, not charging (voltage is measured across a known good battery, fully charged.)

Attachment 36992

And now for the voltage test with Field 1 grounded charging wide open

Attachment 36993

The alternator is good. This means that the ECU which controls the variable ground that is supplied to Field 2 has failed.

The unit on the left is reconditioned with what looks like three capacitors changed out. The gel media has been "picked" out, and I'm not about to pull it out just to see what else might have been done.

Attachment 36994

I got this off ebay from a company in Fort Lauderdale (I don't know if I'm allowed to say the name of the company on here). It was $249 plus $25 shipping and has a lifetime warranty to the purchaser, meaning you can't transfer it to anyone you sell your jeep to. (The local auto parts store was $212 and 90 days) Also, you must return the old unit to activate your warranty and they'll charge you a $75 core as well if you don't.

They say the test them under vibration, heat, and cold, and flash the eprom with the latest firmware for your year and model.

I hope this help anyone else who has alternator problems. Please feel free to contact me

89JEEPYJ 02-05-2011 04:46 PM

it could also be possible that its a bad battery. Whats ur Volt meter say in ur gauge cluster?

AzTJ 02-05-2011 05:37 PM

Do no disconnect the battery on vehicle with alternators. This was a trick with generators. :thumb:

And easy upgrade is to get a newer alternator that has a built in voltage regulator.

callbox47 02-05-2011 09:57 PM

@89JEEPYJ - The battery is known good and fully charged. The volt meter in the gauge cluster is no way as accurate as the meter that I'm using which is accurate to 1/100 of a volt.

@AzTJ - You are right, I shouldn't have disconnected the battery with the engine running. After I did a little reading I found that this is not good practice and won't ever do it again. Thank-you.

Won't having a internal regulator cause the ECU to throw a code?

AzTJ 02-05-2011 10:12 PM

Possibly, but I remember there being a write up somewhere on the internet on how to fool the ECU.

callbox47 02-06-2011 07:24 AM

I found this but I haven't had time to study it completely. I'll check into this later this week and call them to see what installing this does to the ECU as far as check engine codes.

Chrysler Dodge & Jeep Alternator ECU External Voltage Regulator Bypass

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