Scotty, I have a 2015 Kia Optima. 104k miles. 2.4 liter. GDI. Automatic. When I use 87 octane my engine knocks. If I use 89 octane it doesn't knock as much. If I use 91 or 93 octane the engine doesn't knock at all. Could it be a dirty fuel filter, or do I need to get the injectors pressure cleaned? Could it be something else? I also get a high pitched whine when accelerating hard above 4000 RPM. Thanks.
What fuel does the manufacturer specify for that car? If they state that it can run on regular gas you probably have a bad knock sensor. On the other hand if they specify premium fuel then that's what you need to use to avoid engine damage.
Scotty explains why this happens in his video.
https://www.youtube.com/watch?v=BIycEyNci1o
GDI engines need to be cleaned regularly.
I also get a high pitched whine when accelerating hard above 4000 RPM.
Can you please make a YouTube video of the noise & post the link here?
Does it whine if you rev up the engine >4000 rpm while stationary, in Park?
Section 1 page 3 of your owner's manual specifies minimum 87 octane fuels for your vehicle.
If the engine is knocking with 87 octane fuel, your ignition timing is too far advanced or there are other problems that need to be addressed.
You definitely have an issue. You should not need over 87 for that vehicle.
