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Old 03-10-2019, 12:59 PM   #1
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Join Date: Feb 2019
Posts: 3
Default Charging issue - pegs gauge over 2000 rpm and interior lights go out

I'm putting the backstory on this in case anyone has seen anything that may tie these things together. I've been patient, understanding that a 10 year old car is going to have issues, but I'm now at the point where I seriously regret buying it.

I've got a 2008 GT, automatic, stock.

Jan 24, 2019, I bought the car from Carmax.

Feb 2, just over a week later, the check engine light comes on. It's code P0155, O2 sensor. I take it back to Carmax. They put an O2 sensor in it, claim it was a bad one and they needed a Ford OEM sensor, which still doesn't fix it, so they send it to the Ford dealership, who claims they put the wrong O2 sensor in it, which still doesn't fix the CEL. They conclude that the PCM needs to be replaced, and it takes them until March 1 to do all this diagnosis, approve the new PCM, and have Ford put it in the car. I pick up the car on March 1.

March 2, ONE DAY LATER, I'm driving home and the battery gauge (I'm guessing it's a volt meter) starts to drop, and a block from my house the gauge turns red since it hits bottom and odd lights are coming on in the gauges, the ABS light and traction control light, along with the battery light. The radio was off but came on and reset itself, and the CD changer started clicking. I turned off the headlights and pulled the parking brake while I was sitting at the red light, and that brought the gauge back up where it should be. I got home and checked the battery voltage with the car off, 11.5V. It sitll managed to start the car. With the car running, 11.0V. I charge the battery and on Monday morning, March 4, I take it back to Carmax. They replace the alternator and battery, and I picked it up yesterday, March 8.

Today, ONE DAY LATER, while getting on the highway, I gave it a good bit of throttle and the ABS and traction control lights came on in the gauges again. They turned back off when I let off the throttle. I noticed it continuing to do this, and found that anything over 2000 RPM would cause those lights to come on along with the battery light, and would peg the battery meter all the way to full. Later in the evening I was driving and it happened consistently over 2000 RPM, and if it stayed there for more than a few seconds, the interior lights would turn off, but my headlights would remain lit. Once the RPM dropped, the interior lights would come back on. The fog lights would also turn off when this happened, and the radio has reset itself again.

I've heard about the 2010 alternators being a better 3-phase design, but I'm not sure what got put into this car for a replacement alternator. I'm thinking it's the original spec single phase alternator, if I read other posts correctly as to how it came from the factory.

I've attached pictures of the well under the passenger side windshield cowl, and the SJB. Looks to be OK from what I can see.

Any thoughts? Has anyone experienced stuff like this? I'm taking it back to the dealer on Monday morning.

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File Type: jpg 20190310_130756 373x280.jpg (19.4 KB, 3 views)

Last edited by JohnB647; 03-10-2019 at 10:06 PM.
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Old 03-15-2019, 09:11 AM   #2
Drive fast - live slow
Join Date: Mar 2007
Location: Allen, TX
Posts: 1,820

If it will charge at low RPM but not High RPM - the bearings in your alternator are worn out. The worn bearings will let the stator wobble and break the magnetic field. Thus no charging. I would just go back with an OEM unit. They make higher output replacement ones if you want to go that way. I don't think I would try to re-engineer anything.
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Old 03-15-2019, 09:29 AM   #3
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Join Date: Feb 2019
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Thanks S_K. It has had the alternator replaced and is working well so far.
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