Low Charge Voltage Problem
Symptoms
Voltage Gauge on dash reading low. It was OK when starting from cold, reading 14 volts, but voltage would drop as engine warmed up, eventually dropping as low as 11.2 volts.
Finding the problem
Measured battery voltage to make sure this was a charging problem and not a gauge issue. This confirmed that battery voltage was low and dash gauge was reading correctly.
Interestingly at a constant speed on the freeway with the voltage at 11.4 volts I could get the voltage to start creeping back up to 11.8 volts by opening the rear spoiler which presumably brought cool air in to bring the alternator temperature down.
My suspicion was the voltage regulator built into the alternator reducing the voltage as it got hot.
Finding a voltage regulator
Through various sources I found and confirmed that the Bosch number for the regulator in the Porsche alternator is F-00M-145-225. It would appear that this part isn’t actually listed anywhere as a separate item, although I did manage to track one down on e-bay. All is not lost though, as the same part is available under different part numbers. Various websites cross reference the above part number with the regulator for various Volkswagens from the similar years as well as Audi’s and Mercedes. For reference a commonly available part seems to be the F-00M-145-350 or F-00M-145-341 for VW, Audi, and Mercedes which fit perfectly.
These sites reference the different part numbers and various companies offer a replacement part for the Bosch part. These companies usually only have one part number and list ALL the Bosch numbers as equivalents. Here are a few of several possible sources of information. I would like to suggest that you google the part numbers yourself to double check. I have satisfied myself but I cannot guarantee 100%. I can tell you that my car is behaving perfectly with the F 00M 145 350 part.
(Ref;
http://www.woodauto.com/Component.aspx?Ref=VRG46473
OR
http://www.mercedesshop.com/shopforum/archive/index.php/t-187174.html
OR
http://www.jnelectric.com/bombridge.asp?bomtype=wu&lc=BO&partnumber=F00M145350&manufacturer=Bosch&description=Regulator%2C+Electronic )
I suspect that the different vehicle manufacturers insist that Bosch supply parts with a unique part number or that Bosch manufacture identical parts in different locations and assign part numbers to each. If anyone can give me an informed answer to this or if they can tell me if there really is any difference between them I would LOVE to know!
Here is my new selection of Bosch Regulators
Each one in turn, first the 225
The 350 (Also the Mercedes A003 154 53 06)
& the 341
