Wavering Idle and Dropping Voltage

earwicker7

So, I took it in again and the head mechanic said it's nothing to worry about, that it was probably always happening and I just never noticed it. He said that the battery is 12V, and the alternator adds the voltage on top of that. He said it is normal for the voltage to fluctuate between 13-14V when the car needs a little more electrical power. He said that the engine idles a little higher now and then to give the alternator some extra juice.

He did say that it is a problem if it goes lower than 13V; usually, mine only drops to about 13.5V.

Any comments on his verdict?

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2009 Magnetic Black 370Z with Touring, Sports and Navigation Packages--Fast Intentions CBE with 12" Resonators/Carbon Fiber Mufflers and LTH--Stillen G3 Cold Air Intakes, Underdrive Pulley and Grounding Kit--Uprev Tune

dad

Did you try what I posted, post #2?

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v8zracer260z

It is normal to see some fluctuation in the voltmeter depending on the condition of he battery and the loads on the system. Typically 13.0 to 14.5 is a normal range. Though low voltage indicates a non charging symptom ie alternator or regulator problem and over charging sytem can cause more problems. Over charging of more than 15-16 volts can blow out lights and fry computors leading to expensive repairs. In addition to checking the level of the fluid I would recommend checking the specific gravity of the battery acid with a hydrometer found at any local auto parts store. This is a better indicator of battery health. Water has a specific Gravity (SG) of 1.000 in a Sulfuric Acid battery A SG of 1.265 is ideal and it can be slightly higher or lower in each cell but if you have one or more cells showing close to 1.000 indicates a dead or shorted cell it's time to replace the battery. Also since you have a wavering idle that in itself may be causing your voltage to drop. Your alternator puts out very little charge if any at idle. Dropping below that rpm may cause a significant drop in charging voltage. You may not have anything wrong with the charging, but have an idle conrol issue. Just a little advice from a prior F/A 18 Avionics Tech Hope this helps you guys out.

earwicker7

Thanks! I used to have a hydrometer for my saltwater aquarium... wish I'd kept it.

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2009 Magnetic Black 370Z with Touring, Sports and Navigation Packages--Fast Intentions CBE with 12" Resonators/Carbon Fiber Mufflers and LTH--Stillen G3 Cold Air Intakes, Underdrive Pulley and Grounding Kit--Uprev Tune

earwicker7

Yeah, nothing like that. I think I was over-reacting to normal behavior that I had just never noticed.

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2009 Magnetic Black 370Z with Touring, Sports and Navigation Packages--Fast Intentions CBE with 12" Resonators/Carbon Fiber Mufflers and LTH--Stillen G3 Cold Air Intakes, Underdrive Pulley and Grounding Kit--Uprev Tune