EMSJEEP
NAXJA Forum User
- Location
- Long Island
Reading 4 VAC on the alternator to isolator. 3VDC. From battery ground to the field terminals I have battery voltage at one and 1.5-0 VDC at the other while battery voltage sits at 12.3 VDC
Proper Voltage at Alternator Field Control Terminals?
- Thread starter EMSJEEP
- Start date
- Location
- In the islands
Anything could have gone wrong over the time the XJ was not running including the alternator and the isolator. My recommendation would be to remove the isolator completely from the system and check only the battery (one battery) and the alternator. Connect the alternator output wire to the PDC or to the battery + and battery + to the PDC.
Start the engine and bring it up to about 1,500 RPM then trouble shoot the charging system. The alternator functionality could be checked at this time by employing the method I mentioned in my previous post. With a volt meter attached to the battery terminals + and - look for 16 volts. If 16 volts is present the alternator is good and the PCM is bad. If no 16 volts then the alternator is bad.
You did mention you had loose wire/nut I think on the alternator? Why don't you check all wires on the alternator? I would recommend removing and cleaning them then securing them properly. Also, check for +12 volts on that OR/GR wire at the alternator stud when the engine is running. The alternator will not work if it do not receive voltage on this terminal. Did you check all ground wires in the engine compartment? Give them the once over for peace of mind.
EMSJEEP
NAXJA Forum User
- Location
- Long Island
So, nothing worked, nothing produced results. In a moment of red neck anger, I figured that the lose terminals probably crossed and shorted, so I quickly grounded the green wire, nothing there either.
Then I got mad, like, $500 broken alternator mad, and I was like "to hell with you alternator" and I hit the green wire with 12.5v from the battery. Boom, alternator kicked on, brought me up to 14.5v and settled around 14.25/.15 at the isolator and about 13.7 at the battery. Ran it for about 45 minutes watching the voltage on the DMM and everything appears to be operating correctly.
Dunno why that worked, but, it did
Then I got mad, like, $500 broken alternator mad, and I was like "to hell with you alternator" and I hit the green wire with 12.5v from the battery. Boom, alternator kicked on, brought me up to 14.5v and settled around 14.25/.15 at the isolator and about 13.7 at the battery. Ran it for about 45 minutes watching the voltage on the DMM and everything appears to be operating correctly.
Dunno why that worked, but, it did
- Location
- In the islands
That is good that it works. Some things are unexplainable. Keep your eyes on it for a few trips to ascertain it is stable.
EMSJEEP
NAXJA Forum User
- Location
- Long Island
My electrons got stuck...
Will keep an eye on it, and I think some liquid electrical tape on those terminals too.:explosion
EMSJEEP
NAXJA Forum User
- Location
- Long Island
Looks like its not working again...spoke to the techs at Powermaster and they think PCM.
Original question still stands I guess, whats the proper exciter voltage from the PCM?
Original question still stands I guess, whats the proper exciter voltage from the PCM?
Jeep Driver
NAXJA Forum User
- Location
- Parrottsville
Should be 12v
lawsoncl
NAXJA Forum User
- Location
- North Idaho
As I recall, you should have battery voltage to one side of the field coil and the PCM controls the GROUND for the field coil. It pulses it, so it's hard to read with a voltmeter. As others mentioned grounding the wire that goes to the PCM should kick the alternator to full output. If it's not doing that, then the alternator has a probkem. Also, if the PCM is not trying to ground it, and the voltage on the ground wire is low then it may throw a code for a bad field coil (might also throw a code if the field coil looks right but the battery voltage isn't changing).
EMSJEEP
NAXJA Forum User
- Location
- Long Island
Well, I sent the alternator to Powermaster to test/repair and the allstars at Powermaster just sent me a new alternator. They deserve tremendous credit. I’m impressed.
EMSJEEP
NAXJA Forum User
- Location
- Long Island
Factory refurbished alternator did not fix this issue - pulled the PCM connections and they were soggy, but not corroded, cleaned and dried them well and no change. Definitive diagnosis for PCM voltage regulator failure?
lawsoncl
NAXJA Forum User
- Location
- North Idaho
What kind of voltages are you seeing at the field connections? You should see one wire with battery voltage and the other wire bouncing around, probably near zero if the battery is getting drained. Might be worth swapping in a spare PCM to test if you have one handy. Otherwise I'd probably spend a bit more time troubleshooting with a volt meter before shelling out lotsa buck for a new PCM.
EMSJEEP
NAXJA Forum User
- Location
- Long Island
One is roughly battery voltage 12.5-11.3v and the other is a steady .7v.
It actually worked for about 30 seconds this morning when I started it up but I was unable to grab field terminal readings while that was happening.
EMSJEEP
NAXJA Forum User
- Location
- Long Island
Maybe just an external regulator at this point....have it on standby after I rip everything apart...
tonywater18
NAXJA Forum User
- Location
- dallas
How I hate this stuff with the voltage and wiring. It's good that I have a friend who solves all my problems, but I can't turn to him for every little thing. I feel stupid when I can't solve a trivial problem, thanks to this topic, I tried a lot on your advice, but I still have a problem with the air conditioner. Can you tell me if I can trust you here about this ? I also thought to find a good site with an overview of the tools can you tell me if you can trust the public and advertising ones ?
DrakeHeyman
NAXJA Forum User
- Location
- USA, NY
Yes, man, I understand you perfectly, I would not have coped with many problems myself, before there were no problems with wiring and voltage for me. I couldn't even just attach a shelf or solder 2 wires, my problem was the fear of electricity and voltage and the right tool, you can trust me and see what you need https://thetoolscout.com/what-size-generator-do-i-need-for-my-camper/ without further ado and marketing, I'm always looking for reptiles there, my cousin checks them out and supplements them whenever possible. I can trust him as much as I can trust myself so let's say I've solved your problem )
lawsoncl
NAXJA Forum User
- Location
- North Idaho
Welcome!
is a great site for technical help. https://www.cherokeeforum.com/f2/ is also a good resource, with more traffic although personally I think the noise to expertise ration is better here.Start a new thread with your question. Be sure to include relevant details like what year and engine.
tonywater18
NAXJA Forum User
- Location
- dallas
Welcome!
Start a new thread with your question. Be sure to include relevant details like what year and engine.
Thank you very much for really helping, now I will use the site that you advised as often as possible and https://thetoolscout.com/what-size-generator-do-i-need-for-my-camper/ which were suggested to me in a similar topic. What would I do without good people? I would sit without light, without water, and without transportation. This will be the end of the game. On more often, you could find real tips, good sites, and not spam links that lead nowhere. The question remains one, but it is a little off-topic, how does cashback work on the Internet, sorry, but who knows?
