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Hi I have a 9th gen Si with 325k km which has a cylinder 1 misfire with multiple codes (P0301, 83-11, 85-01, 41-11). I checked spark plugs, coils, compression (somehow at 210psi), and injectors which are all good. What would be my next steps to diagnose what's going on? Thanks Codes Compression Test
Valve Adjustment: This is mandatory for high-mileage K-series. Tight exhaust valves are notorious for causing P0301 misfires on these engines, even if cold compression looks okay.
Leak Down Test: A standard compression test doesn't always catch a burnt valve or carbon buildup issues. This will confirm if the cylinder is actually sealing under load.
Check Ground G101: It's located on the intake manifold. If it's loose or corroded, it can cause those VSA communication codes (83-11/85-01) and ghost misfires.
VTC Actuator/Solenoid: Check the VTC screen for debris. If the cam timing isn't advancing properly, it can cause misfires, though usually on more than one cylinder.
Does the misfire happen mostly at idle or under load?"
2012 Civic Si Misfire
