Vehicle: 98 Ram, 5.2L, 2WD, 140 amp output alternator.

When the engine is cold and the battery is fully charged, my alternator outputs 13.7 VDC. After the engine reaches operating temperature, the truck begins to run rough. The dash voltmeter indicates a gradually dropping output (verified by a direct check of alternator output) as the engine continues to run. Within 15 minutes, the engine will not idle. Continued operation drains the battery as the alternator fails to charge the battery and power the car's electrical systems. A short duration bench check of the alternator yields good output. My OBD analyzer says nothing more than the obvious: low alternator output.

This engine's alternator regulator is integrated in the PCM. Short of replacing that expensive unit or the alternator, I want to eliminate a bad sensor (or good sensor reporting a legitimate problem) as the problem.

Anybody out there have any ideas?


Thanks,
Bob in Birmingham, AL