Alright I have a 2002 Ford Taurus that has PCM controlled 4G alternator with a Diehard platium 100ah and a C&D Tech 93 ah batteries. So here's comes the story.
My first alternator was a powerbastards 220A. It put out next to nothing at idle and would drop my system down to 12.0v. When I would accelerate from idle it would spike the voltage to 15.5v+ for a split second and then go back down to a steady 14.2v. Also, if I would roll all my windows up at once the voltage would drop down from 14.2v to like 14v but as soon as I would stop, my voltage would spike up to like 14.8v back down to the constant 14.2v. These spikes eventually resulted in killing one of my HID bulbs and me sending back the alternator.
I then had my stock alternator rebuilt as a high output. It too had the same low output at idle but it didn't have the voltage spikes when accelerating from idle. At cruise it was great but the low idle voltage resulted in me returning that one also.
I now have a Mechman 240A and initially I got no output of it at all but a simple shorter belt change fixed that. I now get 14.4-14.7v at crusing speed but at idle my voltage dips down to like 12.8v-13v not as bad my older ones but still not acceptable. My stock alternator would always hold 14v+ at idle. I clamped it with my meter and got about 53 amps at a 650 rpm idle in park. When I put it in drive it goes even lower. Also, similar to my initial powerbastards alternator, it does the same 15.5+v voltage spikes when accelerating from idle. Another thing is that my voltage drop when I'm blasting seems to be similar to the voltage drops I saw with my stock alternator. I would expect to atleast stay in the 14's at full tilt when starting from 14.7v. Right now I've seen as low as 13.2v drops before my clipping light comes on.
My main concerns are the voltage spikes screwing up my HID's again and figuring out how to raise the idle output. What could possibly be causing the voltage spikes? A bad regulator? Belt? And would an even shorter belt help with the idle output? The belt tension is within spec according to the tensioner tension indicators.
Any help would be great guys. Thanks
Here's a thread on a Taurus forum I made that might have a little more background info
Mechman Alternator - No output - Taurus Car Club of America : Ford Taurus Forum