richardkoehler1
SM5 Knocking Combustion Issue
Summary of the thread
The conversation centers on a knocking combustion issue in a 2007 Renault SM5, characterized by reduced engine power, jerking during acceleration, and smoke, with an error code stored in memory. The suspected cause is deposits in the combustion chamber. A suggestion to check the knock sensor and fuel octane was made, but the focus remained on deposits as the likely culprit. The problem was resolved by having a mechanic clean the combustion chamber, which eliminated the knocking issue.
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4 comment(s)
richardkoehler1 (community.author)
Thanks for the quick reply. I haven't checked the knock sensor directly, but the error code doesn't specifically point to it. I've consistently used the recommended fuel grade. Could deposits in the combustion chamber really cause such significant issues, even with proper fuel?
robertblaze7
Yeah, the deposits can definitely cause pre-ignition, which the knock sensor might not directly flag. I ended up taking mine to a workshop, and they confirmed deposits were the problem. Saved me a lot of headache. I'd suggest getting it checked out.
richardkoehler1 (community.author)
Appreciate the insight. I'll schedule an appointment with a trusted mechanic to inspect the combustion chamber for deposits. Turns out you were right. The mechanic confirmed significant deposits. They cleaned everything out, and the knocking is gone. Cost me 425€, but well worth it to have the car running smoothly again.
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RENAULT
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SM5
robertblaze7
Sounds familiar! I had similar symptoms with my SM5. Reduced power and jerking were the worst. Have you checked your knock sensor? Or considered the fuel octane you're using?