Low voltage at idle
05-19-2008, 04:02 PM
#1
Low voltage at idle Car is a 2001 Formula with LS6 H/C, LTs, 85mm MAF, and slightly modified programming. Automatic, idles at 550rpm. Fan temps are 208-198F and 218-198F.
This is an intermittant problem that I have noticed recently as the weather has gotten hot again. In gear with my foot on the brake the voltage gauge will drop to right above the yellow zone, which I assume is maybe around 11-12V. If I give it some gas or put it in park or neutral it seems to go up to 13V. Usually it sits at 13V at idle or even when moving, except that it has shown about 14V ith the headlights on. Today I tried to check the connections to the battery and alternator and they seemed secure. I don't think the belt is slipping. I haven't heard any slipping noise and the belt seems pretty tight. I also let it idle and it seemed to be at a little over 13V after I started it up, and then 14V after I flipped the headlights on. After sitting and idling for a little while it seemed that the voltage started to creep down a little bit. the fans were running at high speed, but I don't believe the voltage change occurs at the same time the fan speed goes up. It is about 95*F outside today according to the weather. I noticed something similar on a short trip over a week ago when it was also hot, but in between we have had some cool days and I didn't notice it.
I was thinking perhaps the alternator is going out and cannot provide the proper voltage at idle when hot. Does that seem reasonable? What else do you think it could be? Like I said, as far as I can remember it usually idled around 13V, maybe even a hair lower than 13V but I don't recall it ever brushing the yellow marks on the gauge.
This is an intermittant problem that I have noticed recently as the weather has gotten hot again. In gear with my foot on the brake the voltage gauge will drop to right above the yellow zone, which I assume is maybe around 11-12V. If I give it some gas or put it in park or neutral it seems to go up to 13V. Usually it sits at 13V at idle or even when moving, except that it has shown about 14V ith the headlights on. Today I tried to check the connections to the battery and alternator and they seemed secure. I don't think the belt is slipping. I haven't heard any slipping noise and the belt seems pretty tight. I also let it idle and it seemed to be at a little over 13V after I started it up, and then 14V after I flipped the headlights on. After sitting and idling for a little while it seemed that the voltage started to creep down a little bit. the fans were running at high speed, but I don't believe the voltage change occurs at the same time the fan speed goes up. It is about 95*F outside today according to the weather. I noticed something similar on a short trip over a week ago when it was also hot, but in between we have had some cool days and I didn't notice it.
I was thinking perhaps the alternator is going out and cannot provide the proper voltage at idle when hot. Does that seem reasonable? What else do you think it could be? Like I said, as far as I can remember it usually idled around 13V, maybe even a hair lower than 13V but I don't recall it ever brushing the yellow marks on the gauge.
05-19-2008, 04:32 PM
#2
I forgot to mention, I had searched and seen conflicting information about the electrical system. Some say that 11-14V is normal and if so I suppose my car is still within spec as the needle hasn't actually moved into the yellow zone, but other say it shouldn't really ever go below 13V. So I would also like some clarification on that if possible.
05-20-2008, 08:54 AM
#4
You'll see a voltage drop at idle when the fans are running and the A/C is stressing the engine. If you don't have the issue when the fans and A/C are off, you are probably OK.
Your voltage should read in the 13V neighborhood. Your battery also isn't really 12V and should measure a bit higher. (If I remember my battery chemistry correctly, its actually around 12.8V in its ideal state.)
Your voltage should read in the 13V neighborhood. Your battery also isn't really 12V and should measure a bit higher. (If I remember my battery chemistry correctly, its actually around 12.8V in its ideal state.)
05-20-2008, 01:29 PM
#5
Staging Lane
Join Date: Dec 2007
Location: odessa, tx
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same thing is happening to my car , i live in el paso hot as hell last few days and my volts dip down right into the red and trips a code at idle then start driving gets back up to 13v. i have had everything tested all came out ok, been told by the dealership is probably a sensor i didnt believe him at first but did a seach on here and it could actually be a sensor. that will be my next step im also going to take the optima battery out of my truck try it in the camaro see what happens. ill keep you posted
05-20-2008, 02:22 PM
#6
Yeah it looks like this is really an issue with my adaptive idle tuning. The voltages look good and the battery measured alright with the voltmeter. The idle tuning was done back in the fall and I suppose the temperature hid the issue a little.
