Voltage drop at Idle?!?

[281CI96Coupe]

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]

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

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

 

[Ordie]

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]

I know, but it wasnt like this last summer, oh well.

 

[smasher41]

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]

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]

Mine is goofy like that too...never had a real problem.

 

[03ghoststang]

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]

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