2014 Kia Optima 2.4L Engine Losing Power After 10 Minutes

I’m experiencing an issue with my 2014 Kia Optima with a 2.4L engine and could use some guidance. Initially, the car runs smoothly when I start it cold in the morning, with good acceleration and no problems. However, after about 10 minutes of driving, it starts losing power, struggles with acceleration, and begins to make knocking sounds. I also notice a delay in gear shifting and hear some unusual noises.

The situation worsens when I turn on the AC—the car starts shaking and vibrating. I recently replaced the spark plugs (3 days ago) and the battery (this morning), but the issue still persists.

Here are the symptoms in more detail:

  • Loss of acceleration after about 10 minutes of driving
  • Knocking sounds from the engine
  • Delayed shifting of gears
  • Increased engine noise
  • Shaking and vibration, especially when the AC is on

Does anyone have any ideas on what might be causing these problems? Your advice would be greatly appreciated!

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It’s possible that your alternator isn’t charging the battery.

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I checking the voltage for battery while car of it was like 11.9 And while car engine on its 14.9

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Are there any warning lights on the dashboard? I suspect your alternator might be failing, but if it were the alternator, the car wouldn’t start again.

Actually not but I woke up this morning and found the battery completely passed away and no electricity in car I cannot ensure that maybe i forget any light on or what causes happened

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Generally when a car dies in the way you’re describing (i.e. It runs for a short time then starts displaying electrical issues) it’s an alternator/charging issue as a battery is designed to start the car not run it.

But I’m perplexed at your repeated issue. Are you jumping the car a lot?

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Actually, I checked the Scan tool and it said that left headlamps short to ground and also the headlamp light so down