hannes_moore6

Seat Mii Knocking Combustion Issue

My 2020 Seat Mii with a gasoline engine is giving me headaches. It has 186000 km. I'm experiencing what sounds like knocking combustion. Engine power is noticeably reduced, and it jerks when accelerating. There's also smoke when accelerating, and the error memory has stored a fault. My initial thought is deposits in the combustion chamber. Anyone had a similar issue?

4 comment(s)

Oh dear, your description sounds awfully familiar! I had a similar experience with my Seat Mii. Reduced power and jerking, it was quite alarming. Although, I didn't experience any smoke, that sounds rather worrying! My mechanic mentioned something about using high octane fuel. Have you considered a different fuel octane rating? Are you experiencing any piston slap?

Interesting. I've always used standard unleaded, 95 RON. Higher octane, like 98 RON, might help? Also, were there any errors stored in your ECU? Did the mechanic check the knock sensor or ignition timing?

Yes, the error codes I got pointed to combustion issues, and yes, higher octane fuel did make a noticeable difference, it minimized the effects but the problem was still there. The knock sensor was checked, and ignition timing was adjusted as well, but ultimately, cleaning the combustion chamber was the only thing that fixed the problem completely. Honestly, given the smoke you're seeing, I would strongly suggest a visit to a qualified mechanic. Don't want to risk further damage!

Appreciate the insights. Took it to a workshop, and they confirmed combustion chamber deposits were causing the knocking. A cleaning service plus some fuel system treatment appears to have resolved the issue. Total cost was 425€.

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