Electrical Charging Issue

Discussion in 'SN95 4.6L Mustang Tech' started by COramprat, Jul 15, 2013.


  1. COramprat

    COramprat Drone Driver Mod Dude

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    I've had trouble in the past with alternators in my car. I replace the original (came with the car and had the Saleen pulley so I assume original) when I started having fuel pressure issues earlier this year. The second one crapped out when I got it back from the fuel pressure fix. Tested bad output.

    This time the battery light would flash but then go off after the car warmed. I ran a datalog and it always charged around 13.5-13.7 volts no matter what the light was doing. After driving awhile the light would come back on and off but I didn't log it. It seemed to get a little better when I manipulate the alternator connector until today. The light wouldn't go off so I plugged in the tuner and watched the voltage. At speed it was anywhere between 11.3-11.7 volts. I got off the interstate to see if the connector may have worked lose and the voltage came back up to 13.5-13.7.

    Once I got going the voltage would drop again and I noticed that anytime the RPM's were above 1700 the voltage would drop but running below 1700 or at idle the voltage would come back up to 13.7. Could that connector be the cause of the voltage drop? It's strange that it would immediately drop once I got above 1700 RPM's. Is it also a possibility that I need a stouter Alt since this car is built with a little more boogie in it? Anyone pushing more HP and needed a heavier alternator?
  2. Mattstang04

    Mattstang04 Active Member

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    I have not had issues with charging that could be related to high horsepower. It kinda sounds like the voltage regulator may be a bit over active, I think its internal on these newer alternators. Pop the alternator off and have a local auto parts store check it out. If you have a big stereo or something, I could see you getting a higher output alternator otherwise, I don't see a real need.
  3. COramprat

    COramprat Drone Driver Mod Dude

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    That is what I kind of thought. But something is drawing power down and damned if I can't figure out what it is.
  4. COramprat

    COramprat Drone Driver Mod Dude

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    Alternator tested bad output. So I'm on alt #3 since February.
  5. bhuff30

    bhuff30 Founding Member

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    I would go through the alternator wiring and grounds to make sure everything is clean and secure. The alternator is internally regulated and there are only a couple wires going to it. Check the main alternator wire going to the battery, especially near the battery side, along with all connections and terminals. Clean up any corrosion you find and re-secure. Also, make sure the grounds going to the engine are good. Maybe one is coming loose, causing extra load on the alternator.

    That is very unusual for a 3g alternator. The older 2g units were awful... I swear I was replacing them every 10k miles on my 88. :rolleyes: The original 3G on my GT lasted 210k miles. Just replaced it last dec.
  6. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    what car is this on?
  7. COramprat

    COramprat Drone Driver Mod Dude

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    03 GT (Saleen). In my sig above.

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