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Alternator Help! battery wont stay charged

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Old 05-20-2007, 09:49 PM   #1
86onboost
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Default Alternator Help! battery wont stay charged

i had my mustang with a stock alternator, for a while, and the batter wouldnt stay charged. i would cut on the car, and disconnect the battery, and it would cut off, (bad altenator)

well i got myself a new 75amp alternator, and still the same thing, it wont keep the batter charged, we tried optima batterys and duralast, still the same.

Why wont my battery stay charged. Do i need a bigger amperage, or is there a special way to connect it.

BTW its the alternator with the plug, i tried one with a single wire, but still no luck.
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-20-2007, 09:50 PM   #2
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Default RE: Alternator Help! battery wont stay charged

disconnecting the battery to test the alternator... is probably what killed it



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Old 05-20-2007, 11:00 PM   #3
86onboost
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Default RE: Alternator Help! battery wont stay charged

we also went to autzone, and the test was positive, but the car is supposed to stay on when the battery is disconnnected.

and the battery wont keep charge, we tried numerous of batteries.

we tried 2 plug alternators, and 1wire one, and still no luck.

do you think its the amp size , maybe 75 aint enough

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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-20-2007, 11:13 PM   #4
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Default RE: Alternator Help! battery wont stay charged

do you have underdrive pullies, a simple question but you never know
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Old 05-20-2007, 11:17 PM   #5
86onboost
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Default RE: Alternator Help! battery wont stay charged

yes , i am supercharged, i have the supercharge pulley, crank pulley, alternator pulley ( relocated to bottom) and water pump pulley, thats all i running
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-20-2007, 11:29 PM   #6
samseed101
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Default RE: Alternator Help! battery wont stay charged

When the car is running, what does your voltage look like?

And did you say you had underdrive pulleys with a supercharger? Your answer was kind of confusing.
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Old 05-20-2007, 11:41 PM   #7
86onboost
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Default RE: Alternator Help! battery wont stay charged

what im sayin is that the only pulleys i have is supercharger, alternator, water pump, and crank
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 12:07 AM   #8
86onboost
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Default RE: Alternator Help! battery wont stay charged

also the amp i got was a 75 alt. from autzone.

maybe i connected something wrong, can anyone post on how to corretly install an alternator ( the one with the plug)
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 12:25 AM   #9
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Default RE: Alternator Help! battery wont stay charged

anyone?
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 12:29 AM   #10
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Default RE: Alternator Help! battery wont stay charged

75 is a bit low, try a 130 amp from an sn95
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Old 05-21-2007, 12:56 AM   #11
lookin4astang
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Default RE: Alternator Help! battery wont stay charged

Surprised you didn't short something out disconnecting the battery while the car was running. I know a lot of people do it, but it's not a good idea at all. Get yourself a multimeter and start testing some things. Check the battery and alternator first. But DON'T disconnect it while the car is running. You can burn up the alternator, starter relay, and some other things....
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Old 05-27-2007, 06:10 PM   #12
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Default RE: Alternator Help! battery wont stay charged

bump
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-27-2007, 09:38 PM   #13
backfire2007
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Default RE: Alternator Help! battery wont stay charged

I had that problem before, because of my pulleys and my cam the battery wont get enough juice from your stock alt. I bought a 130 amp alt and it barely gets enough juice. do yourself a favor and buy an 200 amp alt to be on the safe side, they aint cheap but you dont have a choice. youll have to trim your alt bracket a little, other than that youll be good to go. I replaced about 5 batteries and a new alt before I figured it out
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Old 05-27-2007, 10:10 PM   #14
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Default RE: Alternator Help! battery wont stay charged

I see your car is an 86 and I am going to guess that your electical system is factory for the most part. OK this may seam off the wall but it is something I have run into with the 4 eyes in the past. On the left hand side of your instument panel is a column of 4 warning lights. Not all of them may be used but a couple should come on when you first start your car. I belive it is the 2nd or 3rd one from the top. check these to see if any are burned out. there is one of those that acts as an exciter for the charging system if that light does not come on when you first start the car your altenator will not send current to the system. It is at least worth a try before you get into more expensive options.
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Old 06-03-2007, 11:55 PM   #15
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Default RE: Alternator Help! battery wont stay charged

I would say get a 200 amp alternator my car works ok with the 130amp durring the day but once night come and the headlights go on it dims and drains the **** outta my car. its worth it, not sure if u need a bigger gauge wire harness for the 200 amp. im trying the same thing let me know if u do it and it works ill get back to u if it works for me
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Old 06-04-2007, 04:38 AM   #16
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Default RE: Alternator Help! battery wont stay charged

+1 on new alt your underdrive pullies draw power from your alt either get a bigger water pump pulley or new alt 130 amp with inline fuse holder to prevent fires
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Old 06-04-2007, 06:01 AM   #17
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Default RE: Alternator Help! battery wont stay charged

Quote:
ORIGINAL: Hoaguestang91

I would say get a 200 amp alternator my car works ok with the 130amp durring the day but once night come and the headlights go on it dims and drains the **** outta my car. its worth it, not sure if u need a bigger gauge wire harness for the 200 amp. im trying the same thing let me know if u do it and it works ill get back to u if it works for me
'i have the same problem and my alt is 140 amp, i have a 200 on my truck that has a big soundsystem and i have to almost turn the volume all the way up to get my headlights to dim, i should have got the 200 for the mustang but i figured 140 would have been enough
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Old 06-23-2007, 10:48 PM   #18
86onboost
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Default RE: Alternator Help! battery wont stay charged

its an 87 5.0 with a painless wiring harness.... I put a new alternator in it.... still no luck.. I changed the pigtails.... rewired everything....

the two black/oranges connectes to the yellow, which goes to the positive of the battery ( or starter relay), and white wire crossover over. and the green wire is for an optional lamp. i have everything
connected except for the green wire. and it still doesnt receive charge.

i took a volt meter, and it read 12.44 volts, when i start the car INSTATLY is goes to 10.2 volts and then downhill from there.

i have no steoro wats so ever... the only electrical things i have is the fan, digital ingition box, lights... thats it.

i tested the alternator and its fine. but it wont charge....???

i still havent figured this out... i pulled the fuses, and the volts dont change they just keep going down.

i think ima buy a 3G alternator and try it..


any advice is needded
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 06-23-2007, 11:50 PM   #19
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Default RE: Alternator Help! battery wont stay charged

i have the exact same problem, do you get any juice from the alternator at all?? if your car dies when the battery is disconnected then you are running completely off the battery, in my opinion a 130amp alt is a good thing to have but will not necessairly fix your problem. From what i understand your alt is not just inseffiecient but doesnt give out charge at all. my stock alt stopped working so i replaced it with a 3g alt froma 95 stang, and just like you dont get any voltage out of it. I also bench tested it numerous times it is turns out good. But when i hook it up it does not charge at all. Now the reason why your alt reads any volt at all is because the power wire is still connected to the battery. If your car is an 87 it should have an external voltage regulator, that could be your problem.That is not the case with my car because the motor is out of a 92gt and the alt has the voltage regulator on it, so the bench test would have told me if it was bad, in your case however if the voltage regulator is not mounted on the alt then the bench test will obviously not tell you if volt regulator is bad or not. Its a $30 part at Kragen and is definately something to consider before you dish out $160 fora 3g. Just my opinion.
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Old 06-24-2007, 01:48 PM   #20
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Default RE: Alternator Help! battery wont stay charged

im am sooryy guys... I left out an important detail.... I have a paxton supercharger at 6 psi, and i change the crank pulley to boost it up to 10psi... the crank pulley that goes to the alt GOT SMALLER, and the one to my supercharger is bigger ( more boost).... DO u think the smaller crank pulley made a difference. should i get a bigger water pump pulley or wat?
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 06-24-2007, 01:48 PM
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