Voltage fluctuations

DiMora

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I have the following symptoms:

Idle voltage 11.5-12.5 fluctuating.

Running voltage @2500 RPM and up: 12.5-13.5 fluctuating.

I am assuming my alternator is going out. Fortunately, I have two spares...so I'll probably just swap it out, but is there anything else to check first? Any voltage regulators external to the alternator, or anything in the under-hood fuse box or SJB to check? Any fuses that blow which can cause those symptoms?

I am not throwing any codes.
 

dysan

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How high are you spinning your engine? I ended up having a custom oversized pulley made by innovators west to slow my alternator down because I was over-spinning mine and killing them. If you have been over-spinning it I don't think a new regulator will fix it since it's the internal wiring that starts losing connection causing the lower voltage.

I need to have a new pulley made for mine at some point since it was made with the offset for the reverse mounted setup with the E-force blower and I have since put my alternator where the a/c compressor used to be.

As for the voltage regulator I believe you can replace it and it's on the back of the alternator. http://www.americanmuscle.com/paperformance-6gw-repair-kit.html
 

702GT

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Yup, dead alternator. Our alternators are internally regulated. Just best to replace.

You can isolate the battery from the alternator just to be sure the battery isn't dragging the alternator, but honestly if you had a dead battery, when you go to hit the starter it is going to drop that battery like a rock. Starter wouldn't even try. Just ditched a battery in the g/f's mustang. Her battery would sit at 12.6 and as soon as you hit the starter it was maybe 5v, wouldn't even click.

If you can start your car, do so. Once the car is running, remove the positive lead from the battery, hit the cable with a multi-meter and check voltage. If it's still shit, you have your absolute confirmation. Just the fact that you can start the car confirms the battery is not dead.

No fuses are going to cause low voltage, except maybe a direct ground, and that will send smoke signals lol.
 

702GT

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Removing the battery leads while the engine is running is no longer recommended. It's possible to fry the ECU that way. Just FYI.

From arc out? Never considered it. The surge happens at the point of arc, but if it's a potential possibility, then you're right.

You could take the alternator to an auto parts store and have them test it, but TBH I have had them test some of mine before and they say they pass, but they are still jacked up. I don't really trust their testers. I'm the type that would just rather replace it than wonder if it's working or not.
 

Saleen4971

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pulling a battery terminal with the engine runnign is bad news on a newer vehicle.

what should these things put out anyway? mine is seeing 13.5v, where as every other vehicle i ahve owned was above 14.....
 

Dino Dino Bambino

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what should these things put out anyway? mine is seeing 13.5v, where as every other vehicle i ahve owned was above 14.....

The minimum should be 13.0v (0.5v above battery voltage with engine off) with no electrical loads but at that level, it's going to be very marginal. At 13.5v your alternator's still OK but only just.
Better have a spare one ready just in case your existing unit goes south. I just recently replaced my alternator and I'm going to rebuild my old one with new bearings/brushes/regulator to have as a spare.
 

BruceH

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It should be 14.2 at idle. I just changed an alternator out yesterday and the new one is crap. I'm getting 11.x to 15.x. I bought the new alternator over a year ago so it's going to be hard to send back.
The old alternator with ground off ears is going back on today. What a waste of time and money.
 

Saleen304

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Voltage is also controlled by the PCM and is lowered to 13.5V when IATs are high. It does this to protect the battery since it thinks high IATs mean high engine bay temps.
 

BruceH

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It should be 14.2 at idle. I just changed an alternator out yesterday and the new one is crap. I'm getting 11.x to 15.x. I bought the new alternator over a year ago so it's going to be hard to send back.
The old alternator with ground off ears is going back on today. What a waste of time and money.

This post was a result of operator error. Upon disassembly I noticed the connector wasn't pushed all the way in. Pushed it in until it clicked, reassembled, and I'm seeing 13.8-14.1.

If anyone is looking for a good working condition alternator with the ears ground off for Roush or DOB use I have one.
 

Dino Dino Bambino

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It should be 14.2 at idle.

Depends on the outside temperature. In the winter the voltage needs to be at the higher end (14.0-14.5) at idle whereas in the summer, a voltage of 13.5-13.9 would be acceptable.
In DiMora's case, it seems the alternator voltage regulator is failing so he's wise to change his alternator before it fails altogether.
 

BruceH

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Depends on the outside temperature. In the winter the voltage needs to be at the higher end (14.0-14.5) at idle whereas in the summer, a voltage of 13.5-13.9 would be acceptable.
In DiMora's case, it seems the alternator voltage regulator is failing so he's wise to change his alternator before it fails altogether.

I got to thinking about it and a better statement for me would of been, "mine has always been 14.2 at idle".

I can't recall off hand what the tune calls for.
 

Pentalab

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I have the following symptoms:

Idle voltage 11.5-12.5 fluctuating.

Running voltage @2500 RPM and up: 12.5-13.5 fluctuating.

I am assuming my alternator is going out. Fortunately, I have two spares...so I'll probably just swap it out, but is there anything else to check first? Any voltage regulators external to the alternator, or anything in the under-hood fuse box or SJB to check? Any fuses that blow which can cause those symptoms?

I am not throwing any codes.

12.4 vdc with eng off. 14.3 to 14.4 vdc with eng on..and idling. The 05-09 alternator's are single phase types. The 2010 alternator is a 3 phase type. A 2010 style will drop right in on any 05-09 car. Single phase alternator's have long gone the way of the do-do bird. I'm surprised ford used em on the 05-09 cars, since most other car maker's used 3 phase types.
 

Dino Dino Bambino

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If your running a cheap under drive pulley set it will cause voltage issues

BBK, Steeda, Real Speed, and ASP UDPs cost around $250 while those from SR Performance cost a mere $157. I haven't heard of issues with any of them on the 05-10 GT.
 

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