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Author Topic: Alternator not charging  (Read 283 times)
01anniversaytj
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Jeep/Vehicle: 2001 Jeep TJ Wrangler
Posts: 58


« on: 04/12/17 - 04:26PM »

So here is the story..

Was re tuning my amp and after i finished had slow crank but started.  Checked running voltage and was only at 12.9 volts, battery is less than 1 month old so i had generator bench tested (passed) however the conductance tester stated voltage regulator failure.  Time for investigation: 

1.  Checked belt for glazing and belt tensioner, - good. 
2.  Battery Terminals - good.
3.  Checked and tested relays in Power Distribution Center - good.
4.  Full Fielded Generator - good voltage.
5.  Checked all connections on generator, starter, PCM and grounds - good/clean.
6.  Back probed voltage at Generator Field Source - Battery voltage.
7.  Back probed voltage at Generator Field - 4.9v no load, 6.9 heavy load.
8.  Checked B+ from generator to battery - same as battery voltage.
9.  Checked resistance on B+ alt to battery - good ohms
10. Pulled battery and tested resistance of battery temperature sensor - 10k ohms from what i remember but in spec.
11. Pulled PCM connectors and tested for ground - good.
12. Back probed pin outs for battery temperature sensor, field source and field - good resistance, no opens.
13. No CEL noted
14. Parasitic draw, volt drops all tested - good.
15. Everything i examined has checked out with no issues found, continues to charge at 12.8/12.9 normal load and 12.7 heavy load.

My only take away is that the External Voltage regulator is not properly pulse width grounding the alternator (although voltage did go up under heavy load at the generator field wire when i back probed it like it was trying).  If anyone has any questions or comments on if i may have forgotten something please feel free to chime in.  Unless i missed something i either have to buy a new PCM or install a external voltage regulator so i just want a second look.  Thanks...

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