Hello all! I have been having charging issues on my 2005 GT (no shaker 1000). I know charging issues have been beaten to death on the forums and the problem often comes down to the alternator. I have read countless forums but have not been able to really pinpoint the issue. I could get another alternator and see if it resolves the issue, but I'd like to have a more definitive diagnosis before throwing parts at the car. Any advice is appreciated.
2021 ~130,000 - Alternator was whining like crazy. Replaced it with NAPA P/N - RAY 2133190 to take advantage of the lifetime warranty. Result: Issue resolved.
November 2023 ~145,000 - Battery light and check charging system came on. Was able to drive the car 5 more days until it died completely . Pulled alternator and installed replacement alternator.

Result: Did not resolve the issue.
Battery was 5 years old, so I figured It was tired anyway and replaced it just to eliminate the possibility.

Result: Did not resolve the issue.
Current state: (battery charged up via trickle charger)

Upon engine start, voltage drops to ~11V +-.5V. - When the car hits ~2500 RPM, the alternator starts undercharging at ~13V+-.3V depending on what accessories are turned on. Remains charging at this voltage until the car is turned off. I have seen very brief spikes up to 14.1V
Unfortunately, I am not sure what these values were with the old alternator.
Troubleshooting:

-pulled new alternator and had it tested by NAPA. Result: passed all tests.

-Brought it to autozone for a bench test. Result: passed all tests

-in car autozone test - voltage Regulation: Fail Diodes: pass



-3 major engine grounds are sound. (Passenger strut tower, block to firewall, alternator housing)

-Parasitic draw measured at ~0.150A (spec is X<0.050A). I do not think a draw of this size would cause the car to undercharge this much.
Measured voltage off the alternator stud to the negative terminal of the battery, same undercharging value.

Thank you for any advice!

 

It sounds like you have another bad alternator. My advice is to steer clear of parts store alternators 'cause they're usually garbage despite the "lifetime warranty". Go to the Ford dealership instead. Their alternators are also remanufactured but they evidently use better quality parts.