Fox Alternator charging intermittently - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 21 Old 08-11-2016, 11:12 PM Thread Starter
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Fox Alternator charging intermittently

92 Mustang, Dart 347, twin turbo, fast fuel management, 240 amp 3G alternator.

The car blew a 200 amp mega fuse in the 4 ga wire from alternator to the battery. I replaced the fuse and now it charges intermittently and the alternator gets quite hot. I have tried running a jumper sense wire to tell the alternator to turn on.

I would assume the alternator is cooked. Anyone have any ideas?

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post #2 of 21 Old 08-12-2016, 12:33 AM
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why did the fuse blow?


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #3 of 21 Old 08-12-2016, 11:02 AM Thread Starter
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I can only take a wild guess and say it had something to do with the alternator getting hot lol. I gave no clue other then the system had a 240amp alternator with a 200amp fuse.
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post #4 of 21 Old 08-12-2016, 11:05 AM
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Just curious, but why are you running such a high amp alternator? Do you still have all the accessories on the motor? Radio/amp system?
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post #5 of 21 Old 08-12-2016, 01:16 PM Thread Starter
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It was on the car when I bought it. The car does run a electric water pump, electric fan and electric fan for the tranny cooler. I figure it's better safe then sorry.
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post #6 of 21 Old 08-12-2016, 06:47 PM
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Quote:
Originally Posted by brienjohnson200 View Post
I can only take a wild guess and say it had something to do with the alternator getting hot lol. I gave no clue other then the system had a 240amp alternator with a 200amp fuse.
the fuse should be sized to protect the current carrying conductor

it has nothing to do with the alt.

so what size is the conductor?

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #7 of 21 Old 08-12-2016, 07:23 PM Thread Starter
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How do I out that? If you mean conductor being the wire; then it's 4ga. If the conductor is in the alternator then I have no idea since I haven't had the alternator apart. It has worked find until recently.
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post #8 of 21 Old 08-12-2016, 07:41 PM
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Current carrying conductor that carries current from the alt to the battery

4awg?

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #9 of 21 Old 08-12-2016, 07:43 PM
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have the alternator tested

..5.95 @ 115, 1.30 60', naturally aspirated.

1991 notch, dart block 427W, , AFR225's, super vic intake, solid roller, UCC 8" converter, glide, Carbureted E85, 28" radial.
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post #10 of 21 Old 08-12-2016, 07:43 PM
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If you blew that size fuse

I would really try to find the short

That is not safe

If you want to have the alt tested take it to someone with a scope to see the size and consistency of the ripple


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #11 of 21 Old 08-13-2016, 10:55 AM Thread Starter
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I had it tested, and it wasn't putting out anything.....but it really seemed like they didn't know what they were doing.
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post #12 of 21 Old 08-13-2016, 01:44 PM
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you can full field it in situ

if it does not load up, its done

if it does, look to volt reg,,,,,

a scope is a much better diag tool, you can see if you have a faulty rectifier

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #13 of 21 Old 08-13-2016, 07:24 PM
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like said above, a better test may show more as to what is going on or what has happened. my gut feeling is that something internal has shorted and cleared, shorted just long enough to cause a high current spike to blow the fuse......now the alternator is toast. look for an alternator rebuild shop, as well as testing it, they may be able to find what component or components failed, it may be repairable.

..5.95 @ 115, 1.30 60', naturally aspirated.

1991 notch, dart block 427W, , AFR225's, super vic intake, solid roller, UCC 8" converter, glide, Carbureted E85, 28" radial.
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post #14 of 21 Old 08-14-2016, 02:03 PM
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With an alternator that big you should run no smaller than a 2awg. It actually should have a 0. Make sure your power and ground cables are matched in size. Something else to consider also, it's absolutely pointless to have lets say, 0 gauge cable and then terminate it with lugs that are too small to fit. Once you begin to trim away strands to make the lug fit, you just took away that cables ability to carry that load safely. It will almost certainly overheat. Also, what pulley size is on the alternator? Under drives are good but in your case, with that much demand, I would make sure I was running the stock pulley.
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post #15 of 21 Old 08-14-2016, 04:37 PM
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Poster can use any size wire as long as it fused protected

But you right, that alt is capable of large current
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post #16 of 21 Old 08-14-2016, 09:30 PM
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Any size wire....... Um, no.
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post #17 of 21 Old 08-14-2016, 09:34 PM
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Sure you can use whatever you want, but from my experience, which melted pretty much everything under my hood, you definitely want a cable matched to the maximum current output. Damn Indy... I hope that was sarcasm... Lol!!!
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post #18 of 21 Old 08-15-2016, 12:19 AM
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you can have a 200 amp alt

have 100 amp worth of load in the car

and have wire rated at 125amps, with a 125 amp fuse,,,,,,and run for the rest of enternity
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89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #19 of 21 Old 08-16-2016, 08:26 PM
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true^^^^. If the regulator is functioning correctly, the alternator only puts out as much as needed. The amp rating is what the alternator is capable of, not what it is producing at all times.
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post #20 of 21 Old 08-19-2016, 11:45 AM Thread Starter
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OK, so I went and replaced the alternator with the stock 3G 130 amp alternator and replace the 200 amp fuse. I know the fuse is too big for this alternator but just for now I tried it. The alternator puts a 14.4 V at idle, but slowly makes its way down to 13 V by the time all the fans kick on and the alternator gets hot fairly quickly. I took the car for a drive and it runs like crap. I'm guessing that once the voltage goes down then the fuel management and the ignition isnt it running properly.
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post #21 of 21 Old 08-19-2016, 05:50 PM
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the fuse has NOTHING to do with the alternator rating

remove all thoughts that it somehow does.

your volt drop is normal, if you don't have underdrive pulleys.

rating of alt is NOT at idle speed.

a 1 million amp alt, will NOT make that at idle speed.

your running issue is NOT from the 13volts at the battery.

time to put your diagnosis hat on.

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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