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  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

ac drops my voltage

  • Thread starter Thread starter syd91GT
  • Start date Start date May 30, 2006
S

syd91GT

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Mar 25, 2006
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#1
  • May 30, 2006
  • #1
I have a 91 GT, and if my air conditioning is on and i'm slowing down to stop it drops my voltage low and my rpm drops low too. It just about stalls my car. Lights play a factor too. If there on at the same time its worse. I don't think my alternator is the problem because my battery is never dead and it runs great if i'm not using those two things, and i need the ac because i live in Texas. It gets HOT in Texas!!! I'm not sure what it is?
 

Roland69

Sergeant Tangnet
Sep 17, 2005
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Port Elgin, Ontario
May 30, 2006
#2
  • May 30, 2006
  • #2
Look into a 3G alt...The stock one from factory isn't up to par
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
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#3
  • May 30, 2006
  • #3
Has the IAC been cleaned recently?

Good luck.
 
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syd91GT

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#4
  • May 30, 2006
  • #4
I got a new one and installed it. That helped because before it would cut out on me at stops.
 
S

syd91GT

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#5
  • May 30, 2006
  • #5
That was the IAC i replaced, but i might try the 3G alternator.
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
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May 30, 2006
#6
  • May 30, 2006
  • #6
The voltage drop is due to the lower RPM's due to engine load more than actual power drain.

Look into installing an OVERDRIVE alt pulley in addition to a 3G alt. It will provide plenty of power for everything. All Fox's should be upgraded to a 3G (and 5-lug ) by now
 
S

syd91GT

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Mar 25, 2006
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#7
  • May 30, 2006
  • #7
Thinks for the info. I do have the five lug conv. with the 1997 17" wheels. I get compliments all the time. That is a must have.
 

jrichker

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Mar 10, 2000
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Dublin GA
May 30, 2006
#8
  • May 30, 2006
  • #8
Figure this:
Ignition system & computer = 12 amps
Fuel pump = 12 amps
Exterior lights = 15 amps
Fan (heater or A/C) = 15 amps (can run between 5-25 amps depending on setting)
Radio & instruments = 10 amps
Wipers = 10 amps

That's grand total of 74 amps from a 65 amp alternator. Talk about overdrawn at the bank!

Here's websites with pictures of the 3G installation...

See http://www.geocities.com/smithmonte/Auto/3G_130A_Alternator_Upgrade.htm - all the tech data you could ever want to know
OR
http://www.mustangcentral.net/tech/alternator.html - excellent pictures of installation

Use these sites for information on the right way to do the wiring. Some people will tell you that you can skip the wiring upgrade, but it will catch up with you sooner or later. A fire in the wiring harness is ugly and expensive.

Under no circumstances connect the two 10 gauge black/white wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

Electric fan = 3G alternator if you want long life & reliability from your car.
The electric fan saves some HP. The stock fan's parasitic drag runs from 7-12 HP depending on who you talk to. The electric fan uses about 1/2 HP of power from the electrical system.

See WWW.partsexpress.com for the fuse & fuse holder.
Fuse @ $3.90 each (need one) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=071-952

Fuseholder @ $5.80 each (need one) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=263-630

4 gauge black wire @ $1.25 a foot (use string to lay out routing & determine length) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-196

4 gauge red wire @ $1.25 a foot (use string to lay out routing & determine length) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-194

4 gauge ring crimp terminals (package of 5) $3.25. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=095-584

3/4 “ Black heat shrink tubing, 4ft length, $3.39
http://www.partsexpress.com/pe/pshow...number=082-058

3/4 “ Red heat shrink tubing, 4ft length, $3.39
http://www.partsexpress.com/pe/pshow...number=082-064

Pre-fab 4 gauge cables with lugs already on the ends are available in most auto parts stores. Look for the starter switch to starter cables.

I am very careful to maintain backwards compatibility, so I did things a little different. The white/black stator wire gets the insulation stripped back about 1 1/2" in the middle of the wire & cut in the middle of the stripped area. Then a short length of white wire with a 1/4" slip on female spade connector gets spliced on to the white/black wire. Slide on enough 1/4" heat shrink tubing on the white wire to cover the solder splice you are going to make. Next all 3 wires get soldered together & the heat shrink tubing gets shrunk. When you finish, the white/black wire looks like a "Y" with 1 white arm and 1 white/black arm. I left the black/orange wires connected to the original plug and did not do anything to them. When you are done, the original plug still has all the wires connected to it and they are still functional. The extra white pigtail wire that you spliced, soldered in & covered with heat shrink tubing is just long enough to plug into the 3G without much left over.

I ran the 4 gauge wire under the front of the engine next to the 4 gauge wire for the starter power feed.
It came up the same path as the fuel injector supply lines, and gets bolted to the power output lug of the 3G alternator. The 125 amp fuse is mounted on a plastic panel bolted to the stock ignition coil mounts. One of side of the fuse has a 4 gauge wire connected to the battery side of the starter solenoid & the other to the 4 gauge power feed wire for the alternator.

I had some 1" silicone aircraft heat shield tubing that I fed the 4 gauge alternator power feed wire through and tie wrapped & clamped it in place with some aircraft cushion clamps. That provided the wire extra protection from road debris and rocks. Some heater hose could be used to do the same thing.

Apart from the grinding I did on the mount bracket, there wasn't much to it. Rather than just grind a notch, I ground the whole web back to the thick part of the bracket. It looks much more factory that way.
 
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syd91GT

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#9
  • May 30, 2006
  • #9
Thats what i'll do. Thanks for the info jrichker.
 

Joey5.0

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Feb 13, 2006
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May 30, 2006
#10
  • May 30, 2006
  • #10
Underdrives pulleys draw alot of current.
 

Roland69

Sergeant Tangnet
Sep 17, 2005
2,867
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58
Port Elgin, Ontario
May 31, 2006
#11
  • May 31, 2006
  • #11
I don't think an under drive would even make much diff on the alt anyway...They spin fairly easy
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
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May 31, 2006
#12
  • May 31, 2006
  • #12
Joey5.0 said:
Underdrives pulleys draw alot of current.
Click to expand...
Only when the alternator's power cable shorts-to-ground through one.
 

Roland69

Sergeant Tangnet
Sep 17, 2005
2,867
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58
Port Elgin, Ontario
May 31, 2006
#13
  • May 31, 2006
  • #13
why Hissin have you hade something like that happen before lol
 

mob

the guy who hits on his mom
20+ Year Stangneter
Oct 3, 2003
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May 31, 2006
#14
  • May 31, 2006
  • #14
I did a battery relocation to the trunk, it wasent the best job because I did it lol, but I didnt pick the best ground. Anyways the result is I really dont have much power. When i brake hard the rpms drop and surge really bad, its died like twice. And sometimes I have surging at idle. At night with my lights on i can see the voltage meter shaking up and down really fast and it moves along with the surging rpm gauge. And one night i turned on my fog lights, parked it at home. Next morning I tried to start it and the battery couldnt start my car, it was dead but needed to be charged. I guess my point is check your ground? lol and that i need to find a new ground for my battery. Goodluck.
 
S

syd91GT

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Mar 25, 2006
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#15
  • May 31, 2006
  • #15
It sounds exactly like the way my car acts. Well I'll look into that to mob. Thanks for the advice. Did you do the alternator swap too?
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
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May 31, 2006
#16
  • May 31, 2006
  • #16
Roland69 said:
why Hissin have you hade something like that happen before lol
Click to expand...
Pulleys dont draw any current.
 

mob

the guy who hits on his mom
20+ Year Stangneter
Oct 3, 2003
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Dallas, TX
May 31, 2006
#17
  • May 31, 2006
  • #17
syd91GT said:
It sounds exactly like the way my car acts. Well I'll look into that to mob. Thanks for the advice. Did you do the alternator swap too?
Click to expand...

No my alternator is stock, but I dont have any acceories really, i dont use ac because it dosent work, and i dont have a radio. Goodluck.
 
S

syd91GT

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Mar 25, 2006
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May 31, 2006
#18
  • May 31, 2006
  • #18
Would the overdrive alt. pulley by itself make a difference or should i do the 3G alt. at the same time? If the pulley works that good, I'll get one tomorrow, and get the alt. later. The 3G is a must, but right now I don't have to much time. Baby number two is on the way ( 1 month more ), so i'm stuck painting and getting his room ready. MARRIED WITH CHILDREN, loved that show.
 
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