[T3] I don't know why yet for some reason my 73 T3 charging system seems off.

[William J]

 I read in the Bentley that the generator rotates 2.3 times the engine speed , My car is an automatic so in park it idles at 1000 RPM in drive warmed up it is 800 RPM , The generator cut in speed in 1450 rpm. The cut in volts is 12.4-13.1. 

 The reason I brought up the cut in voltage is if the gen rpm is 2.3 times the engine rpm so at 800 rpm  x 2.3 = 1840 gen rpm , note I suppose if the gen belt is deep into the pulley the 2.3 would change. 

 I have a VDO voltmeter and checked it's reading aginst my DVOM connected at the battery and they read the same. 

 What stumps me and I should know this yet most of my experience has been with alternators. 

 Why at 1000 engine RPM I read 14.2 VDC and at 800 engine RPM I read 14.1 and as I idle at a stop the voltage drops to 13.5 and the longer I sit and idle it will drop to 12.34 Volts ? As soon as I step on the gas to drive off it jumps back to 14.2 volts. 14,2 volts is the highest reading I will get even at 2500 rpm. Once I shut it off with DVOM still connected the battery read 13.45 volts which is surface charge. It settles to 12.72 Volts over night. To add I don't drive much or very far so I keep a charger connected on the 12 volt 2 amp setting on a timer set for 2 hours each day it sits and after short drives with no less than 4 starts just to keep the battery topped off. 

 I know it's charging and I changed the gen brushes and cleaned every connection on the gen and regulator . What I just can't get is why will idling in drive at 800 engine RPM why does the voltage drop from 14.1 to 13.5 then 12.45 volts ? I know the engine RPM when higher the system puts out more and the reg cuts it down to no more than 14.5 or you would destroy the battery. 

 Is it that the battery is charged enough that the regulator drops the voltage to a point just to maintain the battery?  I didn't see it drop to 12.45 volts before yet usually the warm engine RPM is 1000 when warm in drive sometimes 950 now it's 800. I also noticed that the electric fast idle bypass sat at 1300 rpm for a few minutes now it closes faster since the weather has warmed up. I know the electric air regulator works yet took longer to close . At times when I start the car when the engine is cold yet the outside air temp is say 80* the air regulator never brings the RPM's up past 1000 RPM like it says closed which it shouldn't . I do know when the enines warm and at 800 rpm if I keep my foot on the brake and bring the rpm to 1000 it's back to 14.2 volts. I have no idea why the idle was 1000 in drive and now 800 unless it's related to the air regulator that was not fully closing when I set the idle and I also know that once put in drive from park the load from the auto trans is placed on the engine and will drop the idle , how much is normal I can't say. 

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