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  • SN95 4.6L Mustang Tech

Voltage drop at Idle?!?

  • Thread starter Thread starter 281CI96Coupe
  • Start date Start date Jun 16, 2007

281CI96Coupe

Member
Oct 30, 2006
233
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Jun 16, 2007
#1
  • Jun 16, 2007
  • #1
Ok, I need some help figuring out whats going on with these small voltage drops. Here's the deal when the car is in drive and warmed up, when you come to a complete stop, the voltage drops a few in the word "Normal" on the dash. It usually right near the M but it drops to the "O/R" when you come to a stop. When driving you see the needle go up almost instantly to the M. Doesnt make sense, tensioner pully is going?

I know its not the alternator because when you drive its back to normal settings, and I know its not the battery because, it starts up all the time with no problems. Just lately its been acting like this. Anyone can point me in the right direction?

-Nate
 

the98stang

Active Member
Aug 12, 2005
2,408
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47
Clovis, CA
Jun 17, 2007
#2
  • Jun 17, 2007
  • #2
281CI96Coupe said:
Ok, I need some help figuring out whats going on with these small voltage drops. Here's the deal when the car is in drive and warmed up, when you come to a complete stop, the voltage drops a few in the word "Normal" on the dash. It usually right near the M but it drops to the "O/R" when you come to a stop. When driving you see the needle go up almost instantly to the M. Doesnt make sense, tensioner pully is going?

I know its not the alternator because when you drive its back to normal settings, and I know its not the battery because, it starts up all the time with no problems. Just lately its been acting like this. Anyone can point me in the right direction?

-Nate
Click to expand...

That gauge is a POS...I wouldn't worry about it
 

Ordie

Member
Nov 23, 2004
0
0
7
Key West, FL
Jun 17, 2007
#3
  • Jun 17, 2007
  • #3
That happens. The alternator puts out more when its spins faster, once it slows down the voltage drops only because the RPM's do.
 

281CI96Coupe

Member
Oct 30, 2006
233
0
16
Jun 17, 2007
#4
  • Jun 17, 2007
  • #4
I know, but it wasnt like this last summer, oh well.
 
S

smasher41

New Member
Feb 13, 2007
31
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0
Jun 17, 2007
#5
  • Jun 17, 2007
  • #5
do you have underdrive pulleys installed?

mine does it sometimes also, ive been told underdrive pullies can do it.

just rev it a bit in neutral and it charges back up
 

03ghoststang

Well-Known Member
Jul 16, 2005
1,930
1
57
Los Angeles, California
Jun 17, 2007
#6
  • Jun 17, 2007
  • #6
if you have U/D pullies like mention previously it will do what you have stated ......otherwise chek the alternator output it can be on its way out it should read from 13.6-14.2
 

COramprat

...I can take it. I think.
20+ Year Stangneter
Mar 2, 2003
8,474
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223
Sea of Tranquility
Jun 17, 2007
#7
  • Jun 17, 2007
  • #7
Mine is goofy like that too...never had a real problem.
 

03ghoststang

Well-Known Member
Jul 16, 2005
1,930
1
57
Los Angeles, California
Jun 17, 2007
#8
  • Jun 17, 2007
  • #8
well my 5.0L use to do it with U/D pullies but i switch the alt. pulley to the stock one and it dont do it anymore but i have notice it in certain cars that are bone stock the needle does move a bit
 

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
43,179
17,881
224
Massachusetts
Jun 17, 2007
#9
  • Jun 17, 2007
  • #9
Use a meter on the battery. Have someone rev the engine up and then let it fall to idle and see what you get for voltage. Do it with the accessories on as well

I beleive above 1500RPM or so you should get 13.8-14.5 volts

At idle, anything over 12.0 would still be charging the battery
 
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