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txhokie4life's Avatar
Join Date: Oct 2009
Location: Austin, Texas
Posts: 689
voltage droop

When I have radiator fans on, full blast heater fan, and I am at idle
i notice my voltage drops to ~12v. On a rare occasion it will loose idle.

Normally the voltage range is just a tad off 14v.

It is particularly notable when the radiator fans kick on.

I think I have seen it drop to 12v and then immediately back
up -- other times it seems to hover ~12v. Battery is new (a couple months old) as well.

I've replaced the alternator and it improved from the previous alternator
but still does it. previous alternator was a few tenths volt lower,
and a ~200rpms lower on the idle drop.

I've checked the voltage with both the gauge and with a meter.

what should I be looking for?


2008 Cayenne Twin Turbo
2000 Boxster S
1988 924S Race Car
1982 928 Euro 4 Speed Automatic
1975 911 RSR Replica Race Car
Old 02-11-2011, 09:42 AM
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Registered User
Join Date: Aug 2002
Location: Nor.Cal
Posts: 369
I assume that your vehicle is an early 997...say 2005-06? They had issues with the starter-alternator harness crimps causing excess voltage drop.
Fully loaded and idling: the voltage at your battery can't be more than .5v lower than the voltage coming out of the alternator. I use a curved pick tool and an alligator clamp to reach behind the alternator and contact the terminal with the engine running WARNING: NO ROOM FOR ERRORS here! The belt will eat you leads or sleeves, and probing for 30 power Where you can't see leaves room for arcing to ground (causing you to jump and contact belt).
99/100 early 997's have excessive drop here. Also, if any work has been done on the tranny/clutch there is a power connection on the transmission that can be loose. Good luck! On the otherhand, slot of dealers are goodwilling this repair if yer nice
Old 02-16-2011, 06:57 AM
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