alternator problem

Having a problem with my alternator not charging. It is in a 95 4.0 L automatic transmission four-wheel-drive XJ. The problem started several days ago, it is an intermittent condition indicated by the dashboard gauge showing no charge (12 V or less) and the check engine light most of the time. The exception is on start up after a cold night we have a normal charge ( 14 V) and no check engine light.The alternator has been removed and checked on the bench and shows normal output. Ideas are ranging from bad connections, mostly checked, to a defective ECM and nobody has seen exactly this kind of problem before. Any help will be appreciated.

Where are you having the "bench test" done?

Most chain parts store machines will report a Nippon Denso as "good" when they are in fact BAD.

Article on PCM controlled alternators: http://www.motor.com/article.asp?article_ID=1203

I had an alternator that would fail when hot. Lifetime warranty unit from one of the auto chain stores. They refused to replace it because they tested it as "good" when we took it in. I opened it up and cut the wires to the brushes, reassembled it and took it back. They exchanged it. No more charging problems when hot.