1987 Ford Mustang 2.3

Tiny
MANIAC_3_2000
  • MEMBER
  • 1987 FORD MUSTANG
My alternator at cold start up charges the battery at 14.4 and the alternator putting out 98 amps, with the head lamps, Cooling fans, and AC blower motor running. After about 10 minutes, the charging voltage drops to 12.85 and the amps down to 75. I'v replaced the alternator with a stock 75 amp from napa twice. I just replaced it with a performance 200 amp alternator. So i'm sure its not the alternator itself. I also just replaced all chargeing cables, negative battery to block, and block to car ground. I changed the voltage sensor wire for the voltage regulator. But yet the car still loses its chargeing voltage slowly once its warmed up. The battery is also recently new as once the voltage gets that low it becomes a 5 amp discharge on the battery for everything to continue to run.

All main charging and negative wires are 0 gauge wires.

So with battery and alternator 100 percent not the problem, and main cables. Can someone please help me with this issue.
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Wednesday, June 20th, 2007 AT 9:23 PM

6 Replies

Tiny
MANIAC_3_2000
  • MEMBER
Ok at the suggestion of someone else, I put a reduced pully on the alternator (had one in the garage already) and also got a slightly smaller belt, because performance alternators require higher torque and can slip on oem belts.

Readings are as followed

Cold start
no loads -14.5
add cooling fan -14.5
add lights- 14.5
add AC blower 14.5
2000 rpm 14.5

Now I watched the volt meeter the whole time between cold start and fully warmed up motor. About mid way it was dropped down to 14.0 volts with all the loads applied.

Fully warmed up motor
no loads -14.26
add cooling fan - 13.26
add lights - 13.02
blower motor - (slight incrase in idle for compressor) - 13.4
idle ajusts after 2 minutes - 12.80

2000 rpm - 14.25

I checked for wire's heating up. They were all cool.
The the battery at this point was fluxating from a.8 discharge to a.5 charge.

And lastly the amps at cold start were 109
at warmed up motor it was at 68 amps.
My personal opinion of the matter is that somehow the alternator is either losing its ability to push out (but this would make the 3rd alternator to do this, or somehow something isn' right and is not about to let the alternator know somehow of this drop in voltage, or lastly there is something in the system that has a continus draw of power, but I would assume the alterntor would jump all the way to its max of 200 amps if that were the case. Please tell me what you think, and what to do next.
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Thursday, June 21st, 2007 AT 2:16 PM
Tiny
MANIAC_3_2000
  • MEMBER
Oh maybe I should of mentioned I upgraded the alternator already to a 200 amp with the internal fan style setup, and converted it to a one wire set up.
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Thursday, June 21st, 2007 AT 4:16 PM
Tiny
MANIAC_3_2000
  • MEMBER
Just so we are clear, do you want me to do this with the car started (basicaly start the car then pull the negative post. Or do this with the car off.
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Thursday, June 21st, 2007 AT 4:38 PM
Tiny
MANIAC_3_2000
  • MEMBER
Ok well with motor off and all doors closed, I get a light for only 5 seconds.
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Thursday, June 21st, 2007 AT 5:27 PM
Tiny
MANIAC_3_2000
  • MEMBER
Yep everything is closed, no underhood light. Light comes on the test light for 5 seconds, that's it.
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Thursday, June 21st, 2007 AT 6:31 PM
Tiny
MANIAC_3_2000
  • MEMBER
I assume you gave up? Well does anyone else have any idea of what it could be?
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Friday, June 22nd, 2007 AT 2:37 PM

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