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Author Topic: alternator control field?????  (Read 1947 times)

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cbrads1234

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alternator control field?????
« on: March 09, 2011, 11:03:20 PM »
hi my names cam i have a 91 yj which i have had for over a year now no problems but about two months ago the check engine light would come on and the volt meter would read low if i revved the motor up the meter would read right and check light would go off i did this for a about a month then the light came on and wouldnt go off i took the alternator off had it tested and battery to they both tested fine when i reinstalled them it ran fine again for about three days then light came back on and volt meter dropped to eight i replaced battery and alternator still showing low on volt meter and check engine light and battery is only showing 12.31v across post....any sugestions? i have tried about ten test i got at college off alldata online and cant figure anything out.......
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Offline sharpxmen

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Re: alternator control field?????
« Reply #1 on: March 09, 2011, 11:37:38 PM »
the field is controlled by the PCM

so i would say it's the alternator or the connector that goes in it (not making contact). Or worst case scenario the PCM

could also be the belt but you would hear it in that case.

what did the codes say?
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
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cbrads1234

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Re: alternator control field?????
« Reply #2 on: March 10, 2011, 05:43:55 PM »
with old alternator i got code 41 with new one on i got 47
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Offline sharpxmen

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Re: alternator control field?????
« Reply #3 on: March 10, 2011, 07:31:04 PM »
Quote from: cbrads1234 on March 10, 2011, 05:43:55 PM
with old alternator i got code 41 with new one on i got 47

41 would point to bad alternator or worn brushes

47 means that although the field voltage varies from the PCM there is no voltage variation on the battery (12v+ feed to the PCM) so that can mean either a bad ground or bad connection on the charge wire coming from the alternator. I would take the Jeep to the store you bought the alternator from if the ground and connection is good as it could be something internal. doesn't sound like it's the PCM since it was detected an open circuit before and now has a different code (if it was the same it could have been the PCM).

You could also measure the voltage right at the alternator to see if it's higher than at the battery, that can clarify if it ground or "+" cable.
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
Latest: Corbeau BajaRS heated seats :dance: keeping warm the rear end

cbrads1234

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Re: alternator control field?????
« Reply #4 on: March 11, 2011, 01:19:41 PM »
wow so i feel really stupid but i figured out what it was arked a wrench while takin the old one off and blew the two fifty amp fuses in under hood fuse panel so when i put the new one on the charge was not making it to the battery
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Offline sharpxmen

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Re: alternator control field?????
« Reply #5 on: March 11, 2011, 02:35:28 PM »
Quote from: cbrads1234 on March 11, 2011, 01:19:41 PM
wow so i feel really stupid but i figured out what it was arked a wrench while takin the old one off and blew the two fifty amp fuses in under hood fuse panel so when i put the new one on the charge was not making it to the battery

there you go, so there was no connectivity on the charge wire to the battery - codes really help  :thumb:
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
Latest: Corbeau BajaRS heated seats :dance: keeping warm the rear end

cbrads1234

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Re: alternator control field?????
« Reply #6 on: March 11, 2011, 05:42:46 PM »
yea seriously ha bad thing is im a certified master tech and that slipped by me....... :brick:
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Offline sharpxmen

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Re: alternator control field?????
« Reply #7 on: March 11, 2011, 08:10:37 PM »
Quote from: cbrads1234 on March 11, 2011, 05:42:46 PM
yea seriously ha bad thing is im a certified master tech and that slipped by me....... :brick:

i have a pretty story about those 2 fuses too: I upgraded to an 136amp alternator and didn't upgrade the wiring, drained the battery right out (left the light on at work for 8 hrs), got a jumpstart from a coworker and the fuses would just keep blowing on me...
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
Latest: Corbeau BajaRS heated seats :dance: keeping warm the rear end

cbrads1234

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Re: alternator control field?????
« Reply #8 on: March 12, 2011, 07:24:15 PM »
wow that interesting i was gonna upgrade and then i got to thinking about how i could possibly do that.......thanks for the help though man you can have all the certifications in the world and it helps to have someone else oppinion sometimes ...... you seen any other common problems on yj's cause im really just gettin into this jeep thing i been a muscle head the past fifteen years
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Torch_Ind

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Re: alternator control field?????
« Reply #9 on: March 12, 2011, 08:04:15 PM »
Quote
wow so i feel really stupid but i figured out what it was arked a wrench while takin the old one off and blew the two fifty amp fuses in under hood fuse panel so when i put the new one on the charge was not making it to the battery

Quote from: cbrads1234 on March 11, 2011, 05:42:46 PM
yea seriously ha bad thing is im a certified master tech and that slipped by me....... :brick:

certified master tech who doesn't disconnect the batter to change a alt??
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Offline sharpxmen

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Re: alternator control field?????
« Reply #10 on: March 12, 2011, 08:48:32 PM »
Torch is also a certified tech  :wall:
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'95 YJ, NSG370 6spd / Hurst shifter, Dana 300 + 4:1 Doubler / tri-stick, Custom skid, Super D35 / Auburn LSD / 4.88, 35x12.5x15 BFG KM2, 64mm t/b, 1.7 RollerRockers, MkVIII e-fan, Dual Diaph Booster
Latest: Corbeau BajaRS heated seats :dance: keeping warm the rear end

Torch_Ind

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Re: alternator control field?????
« Reply #11 on: March 13, 2011, 09:04:07 AM »
Quote from: sharpxmen on March 12, 2011, 08:48:32 PM
Torch is also a certified tech  :wall:

LMAO  :roflol:  Thanks sharp
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cbrads1234

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Re: alternator control field?????
« Reply #12 on: March 13, 2011, 04:58:04 PM »
yea man i was very pissed at this thing cause when i got it .... it was fine now it one thing and another and i dunno why i didnt disconnect the battery
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