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Discussion Starter #1
So I tried to find an answer for this but no luck. Here is my problem:
This has happen twice to me. Car starts and runs fine. I would do about 10-15 miles, pull up to a stop sign or light where I have to completely stop the car, than the rpm will drop to about 300, car starts to shake, battery light comes on, and if I don't give it gas it will shut off on me.

As far as battery usage in the car I had all of these on in the same time. AC, daylight running lights, halo fog lights, stereo with a Bluetooth connection to the phone, and I also had a OBD-II device plugged in and running. I know that all of these running at the same time could drain the battery quick if the car wasn't running, but the car was running!

The car is a 2014 GT, no tune, no engine mods.

Thanks guys



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Doesn't sound like a battery problem to me. Have you checked your voltage meter ehile this is happening? If so how many volts. Do they drop after you engage the transmission? What's your idle voltage? The 2014 I had did have a lot of battery drain but was easily corrected with an overnight charge but I had to charge it weekly if the car was being driven.
 

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Discussion Starter #3
I don't know the battery voltage when this happens because I don't keep my display on the voltage meter. Usually it is at 14 when you start the car, and it drops to about 13.6 when you use accessories. Sometime 13.2.


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Doesn't sound like a battery problem to me. Have you checked your voltage meter while this is happening? If so how many volts. Do they drop after you engage the transmission? What's your idle voltage? The 2014 I had did have a lot of battery drain but was easily corrected with an overnight charge but I had to charge it weekly if the car wasn't being driven.
 

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Discussion Starter #7
Is there such thing as the alternator can't keep up with the requirements to keep all the accessories running?


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Sounds like you are assuming the drop to a very low idle rpm is due to voltage drop. It could be or it could be the other way around.
How often does the car drop to 300 rpm when stopped? Does it only happen occasionally and only when you have a high electrical load?
What's your normal idle rpm? If normal is around 600 to 700 rpm, i'd first try just the AC to see if that alone drops the rpm. Then I'd try putting on all the electrical loads at the same time to see how it reacts. If it is truly due to the added loads this should tell you at least that.
Then I'd look further into the alternator output and battery condition.
 

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Sounds like you are assuming the drop to a very low idle rpm is due to voltage drop. It could be or it could be the other way around.

How often does the car drop to 300 rpm when stopped? Does it only happen occasionally and only when you have a high electrical load?

What's your normal idle rpm? If normal is around 600 to 700 rpm, i'd first try just the AC to see if that alone drops the rpm. Then I'd try putting on all the electrical loads at the same time to see how it reacts. If it is truly due to the added loads this should tell you at least that.

Then I'd look further into the alternator output and battery condition.

The rpm is usually at 600-700 when the car warms up. Never dropped below that point, except those two times when I had all the accessories ON. The problem doesn't happen with normal accessories ON (lights, radio, AC) it happened when the OBD-II device was running in the same time as all of the other things.

Anyone has any experience with OBD-II devices? I use it for DashCommand gauges.


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---------- Post added at 08:31 PM ---------- Previous post was at 08:30 PM ----------

What is the normal voltage that the battery should have with accessories ON while driving?


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The rpm is usually at 600-700 when the car warms up. Never dropped below that point, except those two times when I had all the accessories ON. The problem doesn't happen with normal accessories ON (lights, radio, AC) it happened when the OBD-II device was running in the same time as all of the other things.

Anyone has any experience with OBD-II devices? I use it for DashCommand gauges.


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---------- Post added at 08:31 PM ---------- Previous post was at 08:30 PM ----------

What is the normal voltage that the battery should have with accessories ON while driving?

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The voltage at the battery while driving would basically be the alternator output voltage, which should be between 13.3 volts and 14.7 volts.
So it has only happen twice and I assume you're saying that those were the only times when you had the OBD-II device running?
What I'm driving at is trying to duplicate the problem while parked with all the same loads. Do some testing to reinforce your assumptions.
 
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