Low voltage at Idle
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Joined: Nov 2005
Posts: 74
Likes: 1
From: Toronto Ontario
Low voltage at Idle
I Just bought my vette about 3 months ago. I replaced the battery a few weeks ago because the old one wouldn't hold a charge and i was getting low voltage at idle or when the heater, headlight, and radio is on. I just replaced the alternator yesturday and it works great while driving, under load (radio,heater,lights) It's about 12.5-12.8 and if I rev it up the volts stay high, so the alternator is working. But at idle the voltage slowly creeps down to about 10.6-10.8 and the car seems to slightly hiccup (it doesn't sound 100% smooth). Is this normal? Also, When starting the car in cold conditions, It idles extremely low at about 450 and would die unless i gassed it a bit for a few minutes until it warms, then the idle is about 650-700. I wonder If the voltage is low at idle because my car idles too low. Any ideas on how to fix the low idle/voltage? Thanks
Melting Slicks
Joined: Aug 2003
Posts: 3,401
Likes: 397
From: Lakeville MI
This is common with pulley kits. At low rpm, the alternator drops out. Check out your pulley diameters.
There are a couple of options on how to correct. Put a small pulley on the alt so it spins faster, raise the idle speed in the chip, go back to stock crank pulley, if it has been changed.
With my pulley kit (march 3-piece) I need 800-900 rpm to maintain voltage above 12.6 with the cooling fans on etc. This would be ok for a stick car, but could be annoying in an auto.
I have my idle tuned as low a 700 rpm for low temps before the fans come on, so I can hear my cam's lope better. I know its silly but it sounds pretty cool at 700 rpm, and I can get away with it at relatively low temps.
There are a couple of options on how to correct. Put a small pulley on the alt so it spins faster, raise the idle speed in the chip, go back to stock crank pulley, if it has been changed.
With my pulley kit (march 3-piece) I need 800-900 rpm to maintain voltage above 12.6 with the cooling fans on etc. This would be ok for a stick car, but could be annoying in an auto.
I have my idle tuned as low a 700 rpm for low temps before the fans come on, so I can hear my cam's lope better. I know its silly but it sounds pretty cool at 700 rpm, and I can get away with it at relatively low temps.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
I had a low idle voltage condition in my 83' Supra until recently. I had replaced the Battery and alternator and it still had the low idle voltage. A couple of months ago, the Neg battery terminal broke, and upon replacing it, I found LOTS of corrosion INSIDE the cable end. I cut the cable back until I saw clean copper, lubed it up with diletric grease and installed the new negetive terminal. The idle voltage is now where it should be.
Just something else to check.
Just something else to check.
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
Its normal for ALL cars to idle at higher rpms when its cold out. Its how they warm up and why revving it up after you just start it and its cold could possibly damage the engine. Of course you could always get a block heater, but thats more weight.
